This presentation will summarize the U. S. Department of Energy&’s 2011 Critical Materials Strategy and discuss related work by DOE since the report was issued. The Critical Materials Strategy focuses on several energy technologies expected to experience high growth in coming years. Specifically, it highlights the importance of certain materials to wind turbines, electric vehicles, photovoltaic thin films, and energy efficient lighting. It also includes an analysis of rare earth catalysts used in petroleum refining. The report includes criticality assessments, market analyses and technology analyses to address critical material challenges. The analysis is intended to help inform policymakers and the public. There are several highlights of the report. First, a number of clean energy technologies use materials at risk of supply disruptions in the short term. These risks will generally decrease in the medium and long term. Second, supply challenges for five rare earth metals (dysprosium, neodymium, terbium, europium, and yttrium) may affect clean energy technology deployment in the years ahead. Third, priorities are identified for critical materials research. Finally, building workforce capabilities through education and training will also help address vulnerabilities and realize opportunities related to critical materials. Since the report was issued, DOE and other stakeholders have scaled up work to address these challenges. This includes the competition for a Critical Materials Innovation Hub, international workshops bringing together leading experts and substantial new coordination among Federal agencies working these topics.

New technologies and engineered materials create the potential for rapid increases in demand for some elements used previously and even now in relatively small quantities. The most prominent—although by no means only—examples are gallium, indium and tellurium in photovoltaic solar cells; lithium in automotive batteries; and rare-earth elements in wind turbines, hybrid vehicles, and compact-fluorescent light bulbs. These technological developments raise two concerns. First, there are fears that supply will not keep up with the explosion of demand due to the time lags involved in bringing new production capacity online or more fundamentally the basic geologic scarcity of certain elements. Second, there are fears that supplies of some elements are insecure due to, for example, import dependence, export restrictions on primary raw materials by some nations, industry concentration, or the reliance on byproduct production that characterizes the supply of some strategic and critical minerals. In both cases, mineral availability—or more precisely, unavailability—has emerged as a potential constraint on the development and deployment of emerging and important technologies, especially in the clean-energy and defense sectors. This talk will review and discuss economic aspects of these issues and related public policy issues.

The recovery of copper by hydrometallurgical processes including heap and stockpile leaching of ore and certain low-grade materials represents approximately 40% of the primary domestic production of copper. Worldwide these techniques account for about 20% of all copper production. Pregnant leach solutions recovered as part of these operations contain important quantities of metals beside copper. Metals are being continually leached by dilute sulfuric acid from the copper bearing rock. Analyses of these solutions indicate the presence of cobalt, nickel, rhenium, and the entire suite of rare earth elements (REEs) including yttrium. The rare earth elements are especially critical for certain alternative energy generation and efficient energy applications. The concentration of REEs in copper leach solution is very low ranging from 1 to 40 ppm. When one considers the huge volumes of solution typically processed by these operations the metal content is economically significant. This paper discusses the potential of using conventional as well as advanced separation methods for the concentration and purification of selected metals.

One of the potential for lithium growth is the recent interest in the production of batteries for electric vehicles. While this is an exciting potential, the traditional uses still dominate the market demand for lithium compounds. Until about the mid-1990&’s, the production of lithium was dominated by two U.S. companies, which mined lithium minerals in North Carolina and one company produced lithium from a brine operation in Nevada. Several other companies produced lithium mineral concentrates in Canada, Zimbabwe and Australia. Lithium chemicals were manufactured in the Soviet Union and the P.R.C. For many years, the Nevada brine deposit was considered unique in the world. That was thenhellip; In 1969, a study by Chilean Geologists revealed the presence of high lithium concentrations in the interstitial brines of the Salar de Atacama in northern Chile. In 1986, the salar became the second location in the world to produce lithium carbonate from brines. In the mid 90&’s another Chilean entity, SQM - the Sociedad Quimica y Minera -started the production of potash, potassium sulfate, and, from the bitterns, lithium carbonate in the northern part of the Salar. The latter allowed SQM to offer lithium carbonate at nearly half the published price, thereby effectively penetrating the lithium carbonate market. From a non-producer before1985, Chile now supplies 60% of the world&’s lithium carbonate. Following the initial production success in Chile, and the recent increased interest in automotive lithium batteries, exploration for lithium-bearing brines intensified and has resulted in the discovery of lithium in the salars of Argentina (Hombre Muerto, Sal de Vida, Rincon, Olaroz, Cauchari and Diablillos and others), Bolivia (Uyuni), Tibet (Zabuye), and the People&’s Republic of China (Quinghai basin). The paper will analyze the evolution in the production sector, review the main lithium applications and evaluate the potential impact of the electric car on future lithium demand.

Rapidly occurring changes in energy availability lead to the question if energy and materials sustainability are equivalent. The answer is not straightforward because of two reasons: a) the amount of energy or of major materials types that can be diverted from one to the other to allow changes to new energy sources, without disrupting our daily life, is restricted to at most a few percent of the total energy production; b) if the transition to new energy sources requires large quantities of materials that are byproducts of large scale production cycles, this may pose a problem that has no obvious solution at present. The reason is that any increase in the production of a byproduct requires an almost proportional increase in the production of the primary product. Increased production of the primary product may require materials and energy expenditures, which are too large to be practical. Both theses lead to a number of issues that are critical in considering materials-energy interdependence: a) there is very little flexibility in the ability to divert energy resources to new technologies; b) production of those materials that are by-products cannot be increased rapidly, something that imposes severe restrictions on the rate of technology change and c) recycling can provide only a partial relief of the demand for energy to produce materials, because many items with high energy consumption cannot be recycled. d) although production becomes less and less materials- and energy-intensive, because of the introduction of more and more efficient processes, energy expenditure for production of materials may strongly deviate from this trend for a number of reasons, the most obvious of which is depletion of rich ores and increased hauling distances.

Cellulose is the most abundant organic polymer on Earth, found in plants (cotton, hemp, wood), marine animals (Tunicate), algae (Valonia) bacteria (Acetobacter xylium) and even amoeba (Dictyostelium discoideum). Critical features of the structural performance of cellulose in these diverse settings are the large aspect ratio and high strength properties of the cellulose nanocrystals (CNC) and cellulose nanofibers (CNF), which provides nano-scale reinforcement. Acid hydrolysis of the native cellulose is the predominant method used to prepare pure CNC and CNF. Depending on the source of the cellulose and the chemical treatment the resulting material can vary in crystalline type, surface chemistry, dimensions, and aspect ratio. This new class of materials is gaining increased importance due to their novel properties (high strength, low thermal expansion, rich surface chemistry and optical transparency). Primary drivers for their use include their renewability and proven low toxicity. Consequently, several pilot plants and a number of commercial scale CNC manufacturing facilities have recently gone online worldwide utilizing wood as raw material. The applications envisioned range from transportation to biomedical. The use of CNC/CNF to enhance the properties of polymers originated with Marchessault&’s research in1959.1 Recently, this approach has become the focus of international research efforts.2 The development of measurement method which can characterize the structure and morphology of cellulose nanocomposites over many length scales are needed to enable successful manufacturing and product development of cellulose nanomaterials. Our application of laser scanning confocal microscope (LSCM) imaging combined with Forster resonance energy transfer (FRET)3 has enabled multi-scale characterization of the dispersion of nanofibrillated cellulose fibers in a polymer matrix. The LCSM-FRET method has supplied detailed nano-scale interface information, which has been used to inform more detailed structure property force-indentation studies of CNF nanocomposites. The results of these efforts will be presented, along with our recent efforts to characterize the different surface chemistry and morphologies of the CNC/CNF from various sources. 1. R. H. Marchessault, F.F. Morehead, N. M. Walter, Nature 1959, 184, 632. 2. Y. Habibi, L.A. Lucian, O. Rojas, Cellulose nanocrystals: chemistry, self-assembly and applications. Chem. Rev. 2011, 110, 3479-3500. 3. M. Zammarano, P. Maupin, L.P. Sung, J. W. Gilman, D. M. Fox, "Revealing the Interphase in Polymer Nanocomposites" ACS Nano, 2011, 3391-3399.

Traditional assembly line manufacturing is speculative, costly and environmentally unsustainable. It is speculative because it commits substantial resources—energy, materials, shipping, handling, stocking and displaying—without a guaranteed sale. It is costly because each of these resources—material, process, people and place—involves expense not encountered when a product is manufactured at the time of sale. It is environmentally unsustainable because, no matter how much recycling is done, not using the resources unless actually needed is always a better path. As part of the Ragnarok (Research on Advancing Glass & Nonorganic Applications to Recreate Objects & Kinetics) project in HP Labs, we identified glass as a promising candidate for additive manufacturing based on 3-D printing methods. Glass is a silica-based material. With 90% of the earth&’s crust composed of silicate minerals, there will be no shortage of silica resources. Glass is easy to recycle and is environmentally friendly. Only when glass dust is inhaled can ill health effects be associated with glass. Glass is inexpensive but looks precious, is pleasant to the touch and is so familiar that customers will not be disappointed by its fragility—under certain conditions. Glass is versatile. Glass is ubiquitous in time and space—the ancient Egyptians valued glass as precious jewellery, and energy saving light bulbs are still made of glass. Look around in your environment and you will suddenly realize how widely glass is used. But it can also be used in other high tech applications like: Printed electronics Electronic codes (readable by smartphones, tablets or touchscreens) Security printing (color effects, coatings) Functional surfaces for part assembly Tactile surfaces for touchscreen applications Tactile surfaces on objects replacing classic methods; e.g. veneer. Industrial surfaces—sandpaper, polishing surfaces, abrasive surfaces, friction surfaces, etc. Protective films and coatings The basis of all applications is ‘glass ink&’ for 3D printing. To achieve a sustainable, environmental friendly and ‘carefree&’ technology we concentrate on water-based inks. Glass will suspend in water when the particles are small enough but a glass and water mixture alone is not printable. Under pressure the water is expelled from the mixture and jamming occurs. A binder is needed to trap the water between the glass particles. Traditionally polysaccharides are used for glass, see for example http://www.washington.edu/news/archive/id/52160. In small amounts, the sugar will simply burn off during firing: when it is trapped inside the glass object, it will lead to discolouration. We will present alternative approaches leading to transparent glass objects.

Materials scientists today employ essentially the entire periodic table in creating modern technology. In an age of sharply increasing usage, it is reasonable to wonder about the supplies of these elemental building blocks. This talk will present a recent history of resource use trends, emphasizing the rapid recent growth in the use of scarce “specialty metals”. A methodology for assessing relative metal criticality is discussed, and illustrated with a sampling of results for a variety of metals. The implications of criticality and its evolution provide food for thought with respect to the widespread use of metals based solely on their physical and chemical properties, with little or no consideration given to long term availability.

One way to reduce the criticality of materials is to increase their production and recycling on a local basis. This talk will focus on Molycorp&’s Project Phoenix at Mountain Pass, CA, a major expansion, renovation, and restarting of rare earth production in the U.S. after a decade-long hiatus. Molycorp is expected achieve a Phase 1 rate of production of 19,050 tonnes/year in the fourth quarter of 2012, and is expected to expand its production capacity in mid-2013 to as much as 40,000 tonnes/year. Coupled with its additional processing facilities around the world, the Company will produce a wide variety of high-purity, custom engineered, light and heavy rare earths. Molycorp's production will go a long way to reducing the criticality of such key elements as neodymium, europium, dysprosium, terbium and others.

The twin pressures of growing demand for energy and increasing concern about anthropogenic climate change have stimulated research into new sources of energy and novel ways to harvest, transmit, store, transform or conserve it. At the same time, advances in physics, chemistry, and material science have enabled researchers to identify chemical elements with properties that can be finely tuned to their specific needs and to employ them in new energy-related technologies. Elements that were once laboratory curiosities, like neodymium, tellurium, and terbium, now figure centrally when novel energy systems are discussed. Many of these elements are not at present mined, refined, or traded in large quantities. New technologies can only impact our energy needs, however, if they can be scaled from laboratory, to demonstration, to massive implementation. As a result, some previously unfamiliar elements will be needed in great quantities. Although every element has its unique story, these Energy Critical Elements have many features in common. I will describe the shared characteristics of these elements, their roles in emerging technologies, potential constraints on their availability, and government actions that can help avoid disruptive shortages. As an example, I will focus especially on elements that are required for photovoltaic technologies.

Biologically mediated extractive metallurgy promises to be a sustainable and environmentally low impact approach to the production of critical energy materials. Our work focuses on the role microbes may have in the recovery of tellurium and rare earth elements (REEs). The microbes used in our studies are three strains of extremophilic microbes from the East Pacific Rise hydrothermal vent fields: pseudoalteromonas sp., alcanivorax sp., and acinetobacter sp., two copper mine drainage microbes: acidithiobacillus thiooxidans and leptospirillum ferrodiazotrophum, and the dissimilatory metal reducer shewanella oneidensis. These microbes, specifically pseudoalteromonas sp., have shown an unusually high resistance to both tellurium and the REEs with a minimum inhibitory concentration (MIC) of ~0.1mM for both. Pseudoalteromonas sp. has the ability to reduce tellurite (TeO₃^2-) to metallic tellurium (Te⁰) and methylate it forming dimethyl telluride (Te(CH₃)₂). Our investigations into these exact mechanism has demonstrated the direct conversion of various other tellurium compounds, such as tellurium dioxide (TeO₂), and telluric acid (Te(OH)₆) to Te⁰, paralleling that already occurs during standard, chemical tellurium production. Furthermore we have demonstrated the recovery of Te⁰ from cadmium telluride, which lends itself to CdTe solar cell recycling, and recovery from autoclave leach slime, the effluent from copper production. We are currently exploring the role of reactive oxygen species (ROS) in these tellurium transformations and will describe our findings. These microbes also appear to biosorp REEs from solution. When incubated with 100 ppb of the rare earth chlorides they have demonstrated enhanced uptake, extracting >95% of REEs from their medium. During this extraction the microbes fractionate individual REEs resulting in separation factors for neighboring REEs of ~1.2, comparable to current industrial solvent-extraction methods. Finally, we will discuss our research on the interaction between these strains and bastnasite concentrate and how it applies to microbially-aided rare earth production.

Indium (In) is usually produced as a minor by-product of lead and zinc smelting and refining processes, and is used in flat panel display (ITO) and thin film solar cell (CuInSe2, CuInGaSe2), etc. Recently, the pyrometallurgical recycling of In-containing materials has been issued in view of 'Urban Mining' due to very high cost and scarceness of indium. However, the solubility of indium into the molten flux has not been fully understood yet. Therefore, in the present study, the solubility of indium at 1773 K in molten CaO-SiO2-Al2O3 flux was measured under reducing atmosphere. The pure indium (99.99%) contained in a graphite crucible was equilibrated with a purified CO(+Ar) gas mixture in the mullite reaction tube which was heated by MoSi2 heating element. The oxygen potential was controlled by C/(CO+Ar) equilibrium. After equilibrating, the samples were quenched by dipping the crucible into brine and crushed for chemical analysis. The content of indium was analyzed by ICP-AES and that of slag components was analyzed by XRF spectroscopy. In high silica region, the solubility of indium increases with increasing oxygen potential and decreases with increasing content CaO, which is in proportion to the basicity. Also, the effect of flux composition and temperature on the solubility of indium is discussed. The solubility of indium was measured in the low silica melts to ensure the applicability of the established reaction mechanism. The solubility of indium follows different mechanism at low silica region. The solubility of indium at low silica region decreases with increasing oxygen potential and increases with increasing CaO content. Consequently, the optimized flux composition was designed to increase the recovery of indium in the pyrometallurgical treatment of In-containing materials.

The 20th century saw rapid and dramatic improvements in permanent magnet materials. It has been 31 years since the discovery of neodymium-iron-boron and numerous companies and laboratories are seeking to produce a new and superior material. Subjects discussed here are material options, economics of selected materials, manufacturability and recycling. Included in manufacturability are issues of methods, energy consumption, process yields and shape/size flexibility. Recycling is gaining attention due to material cost and shortages and focus on minimization of the waste stream. Need is the "mother of invention" and no discussion would be complete without covering why a new material would be beneficial from an applications viewpoint especially in energy production and consumption. Therefore, an introduction will be provided for applications using permanent magnets and an explanation offered as to why new materials would be beneficial.

Permanent magnets (PMs) are indispensable for the electric, electronic and automobile industries, information technologies, automatic control engineering and many other commercial and military applications. In most of these applications, an increase in the magnetic energy density of the PM, usually presented via the maximum energy product (BH)max, immediately increases the efficiency of the whole device and makes it smaller and lighter. Worldwide demand for high performance PMs has increased substantially in the past few years driven by hybrid and electric cars, wind turbines and other power generation systems. A dramatic improvement in the performance of PMs was made during the 20th century, with (BH)max increased by more than 100 times, as a result of major advances in solid state physics, materials science and metallurgy. However, new energy challenges in the world require devices with higher energy efficiency and minimum environmental impact. The potential of 3d-4f compounds that revolutionized PM science and technology is nearly fully utilized, and the supply of 4f rare earth elements is no longer assured. This lecture will cover the major principles guiding the development of PMs and overview the current state-of-the-art theoretical and experimental research in this field. Recent progress in the development of nanocomposite PMs, consisting of a fine (at the scale of magnetic exchange length) mixture of phases with high magnetization and large magnetic hardness, will be discussed. Fabrication of such PMs is currently the most promising way to boost the (BH)max, while simultaneously decreasing, at least partially, the reliance on the rare earth elements. Current efforts in the development of high performance non-rare earth magnets and their future prospects will also be discussed. Work Supported by DOE ARPA-E and NSF

Advanced permanent magnets containing rare-earth elements are essential to a variety of alternative energy technologies. Due to rare-earth element supply restrictions, there is strong motivation to develop strong magnets that do not contain rare earths. In addition to strategic and geopolitical impact, creation of an ultra-strong rare-earth-free magnet would ensure energy security and provide substantial economic impact. To that end, tetrataenite (Tt) is a meteoritic mineral of ideal composition FeNi with the L10 (AuCu-I) structure and has excellent permanent magnetic behavior. The tetrataenite L10 ordered structure formed at 320C by chemical ordering from the fcc (γ) phase. Unfortunately iron and nickel diffusion is extremely low below this ordering temperature and fabrication of the Tt phase is almost impossible to obtain by conventional annealing processes, with a diffusion coefficient that predicts one atomic jump in 10000 years at 300C [1]. The addition of minor alloying elements such as phosphorus [2], and most likely sulfur and carbon enhance the diffusivity of nickel in iron. To investigate aspects of the formation and magnetic attributes of the Tt phase, selected meteorites containing tetrataenite were studied. Characterization of the Tt phase was obtained using polarized light microscopy, scanning electron microscopy, magnetic force microscopy (MFM) and SQUID. All samples were metallographically polished, using 0.05 micron colloidal silica, to provide a smooth surface suitable for polarized light microscopy and MFM analysis. For MFM analysis a Brucker Multimode atomic force microscope was operated in the tapping mode to capture the magnetic domains of the samples. The topographic images were largely featureless. Magnetic domain images were obtained from magnetic force microscopy performed on the polished portion of the Estherville mesosiderite and characterize a phase assemblage of cloudy zone (CZ) which contains clear taenite - tetrataenite and bcc kamacite. In particular, the CZ appears as a mixture of isotropic submicron magnetic domains. In addition, the clear taenite-tetrataenite in other regions of the metal regions shows stripe- and flame-like magnetic domain features that are diagnostic of a magnetically-uniaxial structure. The existence of multiple L10 variants within a single crystallographic grain is confirmed by the MFM data. MFM data also provide the magnetic domain width d and the saturation magnetization Ms of the Tt. Knowledge of d and Ms provides an indication of the magneto-crystalline anisotropy of the magnetic phase. The outcome of this approach will provide guidance towards the bulk synthesis of the tetrataenite phase on a laboratory time scale. [1] Reuter K B. et al. 1989. Met.Trans.A 20A: 719-725. [2] Goldstein et al (2009) Chemie der Erde 69 293-325 Acknowledgement: Research funded under a cooperative agreement with the U.S. Department of Energy Advanced Research Project Agency - Energy (ARPA-E).

Rare earth (RE) metals are critical to numerous energy technologies; however, supply concerns have increased the importance of developing novel recycling technologies. Here we describe recovering RE metals from magnetic scrap alloys (Nd-Fe-B magnets) via liquid Mg extraction. By utilizing induction melting, the RE metals diffuse into the liquid Mg leaving behind a solid Fe-B matrix. Subsequent vacuum distillation of the Mg-RE alloy has allowed for the recovery of >98% pure RE metals. The effectiveness of this technique, which has been demonstrated on the kg-scale, has been investigated through synthesizing RE2Fe14B-type magnetic alloys from recycled RE metals for comparison with alloys synthesized using pure RE metals. We have compared the intrinsic magnetic properties including the saturation magnetization and the anisotropy field for the different alloys. The effects of impurities on the microstructure and magnetic properties of the alloys prepared from recycled RE metals are discussed.

Concern for the supply of rare earth metals has stimulated the search for alternative magnetic materials. Alnico, with excellent magnetic stability at high temperature, is a promising candidate which was optimized prior to advent of todays advanced characterization tools. Key to the optimization of the magnetic properties is control of the spinodal decomposition (SD) into a non-magnetic phase and an FeCo-rich strong magnetic phase. Thus, understanding the structural relationship between those two phases, as well as influence on processing and chemistry are critical for improving properties of alnico alloys. This objective of this study is a detailed structural characterization of the SD phases in several commercial alnico alloys from Arnold Magnetic Technologies. A fully suite of transmission electron microscopy (TEM) techniques, including diffraction contrast TEM, high resolution transmission electron microscopy (HREM), aberration corrected scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDXs), Lorentz microscopy and off-axis holography were used. HREM TEM imaging shows that the interface between ‘AlNi&’ phase and FeCo-rich phase are coherent. Alnico 5-7 and alnico 8 alloys have distinctly different SD phase morphology, in part due to differences in chemistry. For AlNiCo5-7, the ‘AlNi&’ phase is a B2 order compound, with its primitive cubic lattice aligns with the FeCo bcc lattice ({001} || {001} and <100> || <100>). However, the ‘AlNi&’ phase in AlNiCo8 alloys shows D03 ordering. The FeCo-rich phase in alnico 8 are bounded by {110}, {100} and {111} planes. Moreover, the alnico 5-7 alloys shows higher FeCo-phase volume ratio comparing with alnico 8 alloys. STEM imaging on as quenched (1250 C) alnico 8 alloys shows different SD spacing and morphology comparing with similar alloy annealed at 800 C. Detailed structural study on alnico 9 alloy, as well as Lorentz microscopy and off-axis holography study on magnetic domain structure of those alloys are on going. Supported acknowledged by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technology Office, US-DRIVE program, under Contract No. DE-AC02-07CH11358 for the operation of Ames Laboratory (USDOE).

Facing the shortage of rare earth metals, older permanent magnetic materials are regaining interest. Alnico is rare-earth free and has magnetic properties superior to some rare-earth magnets at high temperatures. The purpose of current research is to characterize the microstructural and chemical features of commercially optimized Alnico 8, supplied by Arnold Magnetic Technologies Corporation. This will set a cornerstone for correlating the magnetic properties to underlying microstructure and should lead to further improvements in the magnetic properties of similar alloys by controlling the microstructure. Complementary characterization techniques, including X-ray diffraction, electron microscopy, and atom-probe tomography, were employed and yielded consistent results. In addition to the primary spinodal phases composed of an Fe-Co phase regions dispersed in a NiAl-based matrix phase, secondary phases of significant volume fraction were observed in this material. The spinodal Fe-Co phase showed a spacing (center to center) of 50-80 nm while their morphology depended on the original solidified grain orientation relative to the magnetic field applied during the isothermal thermal-magnetic treatment, i.e., during spinodal decomposition. The continuous ‘NiAl&’-rich phase has the DO₃ structure and contains a significant amount of Co, Ti, and Cu, rather than the B2 structure observed in alnico 5-7 alloys. The FeCo-rich phase with a body centered cubic structure was isolated by the NiAl-rich phase and contained around 90 at.% Fe plus Co. Secondary phases ranging from tens of microns to a few microns were found along grain boundaries and within grains. In this complex type of spinodally decomposed microstructure, relative to finished magnets of simpler Alnico 5-7, an overarching question remains about the source(s) of coercivity for these magnetic materials, beyond the classical shape anisotropy mechanism. Supported acknowledged by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technology Office, US-DRIVE program, under Contract No. DE-AC02-07CH11358 for the operation of Ames Laboratory (USDOE). Research supported by Oak Ridge National Laboratory's ShaRE User Facility was sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.

Rare-earth elements (REEs) are principle components of strong permanent magnets used in energy and electronics applications by virtue of their high magnetocrystalline anisotropy. Recent limited supplies of REEs have rendered it necessary to explore routes for development of REE-free permanent magnet materials. One route is to create exchange coupled ferromagnetic/antiferromagnetic nanocomposites, such as Fe-(CuMn), due to potential for dramatically enhanced coercivity in exchange-biased nanostructured systems. In Mn-based binary alloys comprised of Mn and transition metals such as Ag or Cu, nearest-neighbor Mn atoms couple antiferromagnetically, whereas next-nearest-neighbor Mn atoms are coupled to one another ferromagnetically. We anticipate that when nanoscaled regions of a Mn-rich alloy are embedded in a strongly ferromagnetic (FM) matrix like Fe, exchange interactions between the predominately antiferromagnetic (AF) Mn-rich component and the FM matrix cause a massive increase in energy product via the exchange anisotropy phenomenon. This investigation focuses on understanding the correlations between the magnetic and structural properties of the antiferromagnetic portion of Fe_x(Cu₃₀Mn₇₀)_100-x nanocomposites, Cu₃₀Mn₇₀. Nanostructured Cu₃₀Mn₇₀ ribbons were synthesized by rapid solidification using the melt-spinning technique. Magnetic measurements on the as-spun ribbons after field-cooling to 10 K surprisingly reveal a linear hysteresis loop with a giant exchange bias (H_E) of ~10 kOe, unprecedented in Cu-Mn alloys. X-ray diffraction shows existence of two face-centered-cubic phases with slightly different lattice-parameters, calculated as 3.750 ± 0.002 Å and 3.744 ± 0.006 Å using the least-squares method. We hypothesize that exchange interactions between nanoscaled regions of the larger phase, Mn-rich and mostly AF, and the other phase, Mn-poor and mostly FM, explain the giant H_E. The as-spun ribbons were annealed at 200, 300, and 450°C. Linear and nonlinear contributions to the susceptibility chi; both increased with progressive heat treatments. At low T, chi;_linear corresponds to the AF magnetic phase, while chi;_nonlinear comes from multiple contributions - a constant background from an ultrahard AF/FM exchange-coupled magnetic phase which remains mostly unreversed in an applied field of -5 T, and a much softer exchange-coupled magnetic phase, unpresent in the as-spun state, whose contribution increases at the expense of the ultrahard magnetic phase as the annealing temperature increases. The softer phase may correspond to the Mn-poor (FM) regions, which grow at the expense of the Mn-rich (AF) regions due to Mn diffusion and homogenization during heat treatment, or to a weakened coupling of FM/AF phases attributed to a reduction of the AF character of the Mn-rich phases as a result of decreasing Mn concentration, both of which would explain the observed rise in chi;. This research was conducted under ONR grant #N000141010533.

Rare-earth (RE) magnets are becoming more expensive and less available for current applications in technology. Previous research has shown that Mn_xGa (x=2-3) has a giant coercive field, 2.5 T, rivaling that of RE magnets.¹ In this project, the Vapor Liquid Solid (VLS) method was used to grow Mn_xGa on Si (100) substrates utilizing Molecular Beam Epitaxy (MBE). The goal is to produce nanoparticles and nanowires of Mn_xGa that will enable us to study the magnetic properties as a function of reduced dimensionality. The catalysts Au and Ga were used. Several techniques were utilized for preparing the catalyst nanoparticles. Au nanoparticle catalysts were prepared in two ways. Commercial 20 and 50 nm diameter nanoparticles of Au suspended in solution were applied directly to the substrate. A second method produced 50-100 nm diameter Au nanoparticles by depositing 3 to 6 nm of Au, followed by annealing at 550°C for 10-20 minutes. For the Ga catalysts, a 20 nm layer of Ga was deposited on the substrate at room temperature then heated to 400°C for one hour to form Ga nanoparticles. The majority of Ga nanoparticles had diameters of 30-50 nm surrounded by larger nanoparticles with 100-150 nm diameters. To obtain nanoparticles and nanowires using the Au catalyst, a 6-7 nm thick layer of Ga was grown while the substrate was heated to 400°C and annealed for one hour. Since Ga and Au are miscible at a relatively low temperature, the Au was able to supersaturate with Ga and produced Ga nanowires. The resulting Ga nanowires had 50-100 nm diameters and lengths of approximately 1 micron. The Ga nanoparticles surrounding the nanowires had diameters of 50-100 nm. A 12-14 nm equivalent layer of Mn was then deposited and annealed at 400°C for one hour. Through X-ray diffraction, the material showed Mn_xGa 112, 312, and 224 peaks correlated with the tetragonal D0₂₂ structure. High-resolution SEM images showed nanostructures on both sets of samples. Those utilizing Ga as a catalyst showed uniform nanoparticles throughout its composition. The samples which used Au as a catalyst had dense regions of nanowires surrounded by regions of nanoparticles. Energy Dispersive X-ray mapping was used to study the compositions of the nanowires and nanoparticles. The magnetic properties of the nanostructures were studied with SQUID magnetometry and found to have a maximum magnetization of 200 emu/cm³. Work supported by NSF-DMR-0907007 and NSF-DMR-0819762. ¹T.J. Nummy, S.P Bennett, T. Cardinal, and D. Heiman, Large Coercivity in Nanostructured Rare-earth-free Mn_xGa Films, Appl. Phys. Lett. 99, 252506 (2011).

Equal channel angular extrusion (ECAE) overcomes many limitations associated with conventional metal deformation techniques and has been used by many groups to consolidate metallic, ceramic, or glassy powders. In the present study, we examine the effects of consolidation by back-pressure-assisted ECAE processing on the microstructure and magnetic properties of gas-atomized Mn- 46% at. Al powders. We extruded powders both in the as-received condition and after mechanical milling using water-cooled Union Process attritors of two different sizes, a small attritor with a 100 g charge and a large attritor with a 1.5 kg charge. MnAl billets were produced by extruding powder from the large attritor at varying temperatures (573-723 K) and at a backpressure varying from 20 to 50 MPa. X-ray diffraction showed that the extruded rods consisted mostly of the metastable, L1o-structured, ferromagnetic tau; phase with varying amounts of the equilibrium γ2 and β phases. Magnetic measurements, performed using a vibrating sample magnetometer, showed a coercivity up to 4.3 kOe and a saturation magnetization up to 98 emu/g.

Calcium is an attractive negative electrode material for use in grid-scale, electrochemical energy storage devices, such as liquid metal batteries, due to its low electronegativity, high earth abundance (crustal concentration comparable to that of iron), and low cost (nearly one-third that of lithium. To assess the utility of the calcium-bismuth couple as the basis for a liquid metal battery, the electrochemical properties of calcium-bismuth alloys were investigated over the temperature range, 450°C to 775 °C, and the composition range, 0 < xCa < 1, by emf measurements using a cell with the configuration Ca(in Bi)|CaF2|Ca(s) cell. On the basis of these data the isothermal discharge curve (cell voltage vs. state of charge) was determined. Over the temperature range, 500-700°C, calcium was coulometrically titrated at greater than 98% efficiency into liquid bismuth electrodes using both LiCl-NaCl-CaCl2-BaCl2 and LiCl-NaCl-CaCl2 molten salt electrolytes.

Although, the lithium based electrochemical devices are proven to be promising power sources, efforts on developing sodium and divalent alkali metal ion based batteries have been reported [1,2]. In recent years, research on renewable energy is gaining attention on developing solid state sodium batteries and low temperature Na-S batteries [3, 4]. However, no systematic approach on synthesizing Na+ conducting electrolytes and electrochemical characteristics seem to be available in literature. The present investigation provides a comparison of the conduction properties of sodium salts such as NaPF6, NaSCN and NaB(C2O4)2 in the liquid phase and in the Poly(ethylene oxide) based polymer matrix. Solubility of the above salts in the mixtures of organic solvents such as ethylene carbonate (EC) and dimethyl carbonate (DMC) and the flash point of these liquids have been determined. Temperature dependent conductivity measurements (273 to 350 K) have been carried out using impedance spectroscopy technique. On the other hand, the above salts have been dissolved in Poly(ethylene oxide) ( Average Mol.wt. 4 × 106) using acetonitrile media. The solution casted 70-100 mu;m thick, free standing films have been characterized through XRD, FTIR, SEM and impedance spectroscopy techniques. It has been found that polymer based electrolytes exhibit dc-conductivity of about 10-7 Scm-1 at ambient temperature. However, on the addition of low molecular polymers the conductivity enhances by two orders of magnitude. In summary, the electrochemical stability window of the above electrolytes with respect to sodium metal and discharge characteristics of sodium ion secondary battery will be presented. References: [1] Advanced Materials and Devices for Stationary Electrical Energy Storage Applications, a report by Sandia National Laboratories and Pacific Northwest National Laboratory. [2] A. S. Aricograve;, P. G. Bruce, B. Scrosati, J. M. Tarascon, W. V. Schalkwijk, Nat. Mater. 4 (2005) 366. [3]A. Bhide, K. Hariharan, Solid State Ionics, 192 (2011) 360. [4] C. W. Park, H. S. Ryu, K. W. Kim, J. H. Ahn, J. Y. Lee, H. J. Ahn, Jr. Power Sources 165. (2011) 450.

In recent years, La-Mg-Ni intermetallic alloys have been a subject of immense interest due to their promising electrochemical properties as active electrode materials for high energy density Ni-MH batteries. Microstructure, stoichiometry and composition are critical factors that influence the hydrogen absorption-desorption properties and electrochemical behaviour of these electrode materials. In this study, La2MgNi9 alloys produced by rapid solidification at wheel surface speeds of 10.5 ms-1 and 4.2 ms-1, have been systematically characterized for their structural and morphological properties. Electron microscopy (SEM, TEM) and X-ray diffraction, shows that this alloy is multi-phase structured, containing PuNi3-type La2MgNi9 (space group R-3m) as the main phase together with LaMgNi4, LaNi5 and La3MgNi14 as secondary phases. The high vapour pressure of Mg and its eventual loss from the melt accounts for the presence of these Mg-deficient secondary compounds. However, with an optimum amount of Mg in the melt, by addition of Mg in excess of the stoichiometric proportion, a nearly homogeneous single-phase La2MgNi9 structure is formed at the cooling rate of 2.1x104 Ks-1. The microstructural outcome of rapid solidification from the melt largely depends on the cooling rate, temperature gradient and growth rate during solidification and both temperature gradient and cooling rate during solidification, decreases with decreasing quenching wheel speed. This investigation shows that rapid solidification is an efficient technique for controlled synthesis of these materials with the microstructure and composition essential for enhanced electrochemical properties.

As a promising cathode material for sodium ion batteries, Na0.44MnO2 has attracted much attention in recent years because of high theoretical specific capacity (128 mAhr/gm), long cycle performance and excellent stability. The techniques adopted for the synthesis of Na0.44MnO2 such as polymer-pyrolysis and solid state reaction are expensive as well as time consuming. Here we report a novel approach to synthesize crystalline Na0.44MnO2 powders via calcination of an engineered solution precursor. In this process, an aqueous solution precursor comprising of sodium and manganese salts was calcined in a furnace to obtain Na0.44MnO2 powders. The phase, crystallinity and microstructures of the calcined materials were investigated by X-ray diffraction, Differential scanning calorimetry-Thermogravimetry, Scanning electron microscopy and Transmission electron microscopy. Electrochemical behavior was evaluated using electrochemical techniques including galvanostatic charge/discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The powders of Na0.44MnO2 exhibited crystalline phase with platelet morphology. Electrochemical characterization indicated high reversible capacity (~127 mAhr/gm at ~0.07 C) with high cycleability (90% capacity retention after 100 cycles at ~0.9 C). The outstanding electrochemical performance of thus obtained Na0.44MnO2 material, makes the solution precursor calcination route a promising manufacturing process for making large scale Na0.44MnO2 electrodes.

We utilize hydrothermal carbonization followed by chemical activation to convert paper pulp mill sludge biowaste into high surface area (up to 2870 m2 g-1) carbons. This green synthesis process employs an otherwise unusable byproduct of paper manufacturing that is generated in thousands of tons per year. The textural properties of the carbons are tunable via the activation process, yielding controlled levels of micro and mesoporosity. To understand the utility of these carbons for supercapacitor applications, we assembled and tested commercial-type 2032 battery button cells. The results for the optimized carbon are very promising: An organic electrolyte yields a maximum capacitance of 166 F g-1, and a Ragone curve with 30 Wh kg-1 at 57 W kg-1 and 20 Wh kg-1 at 5450 W kg-1. Two ionic liquid electrolytes result in maximum capacitances of 180-190 F g-1 with up to 62% retention between 2 to 200 mV s-1. The ionic liquids yielded energy density - power density combinations of 51 Wh kg-1 at 375 W kg-1 and 26-31 Wh kg-1 at 6760-7000 W kg-1. After 5000 plus charge discharge cycles the capacitance retention is as high at 91%. The scan rate dependence of the surface area normalized capacitance highlights the rich interplay of the electrolyte ions with pores of various sizes.

Attention has been recently focused on the two major efficient energy storage devices - those being batteries and supercapacitors. Supercapacitors have proven desirable for application requiring high power densities and fast charging/discharging rates, however the high energy densities of chemical batteries has thus far been unattainable by these devices. Graphene nanoplatelets (GNPs) possesses many of the valuable material characteristics of carbon nanotubes, with similarly high surface area, low electrical resistance, low mass density and high stability. Here we report our recent work of manipulating nitrogen-doped GNPs for supercapacitor application. The data shows that we have achieved around 3 wt % nitrogen content on graphene, the resulted product exhibited 85 wt % enhancement for the specific capacitance.

Renewable energy, such as wind and solar power, necessitates large-scale and low-cost energy storage methods that are capable of providing power so that supply meets demand during the periods that energy is not actively being produced. Capacitive energy methods provide the power density necessary for fast delivery but have been lacking the ability to provide high energy densities. By combining the high dielectric constant of ceramics and high breakdown voltage intrinsic to glasses, glass-ceramic composites are attractive dielectric material for capacitive power storage. Glass-ceramic composites provide ability to approach zero percent porosity, eliminating voids that act as charge concentrators which is the greatest hindrance producing thick film ceramic materials. The dielectric constant can be calculated following logarithmic mixing. By maximizing the amount of ceramic in the glass-ceramic composite system, both a high dielectric constant, notable of ceramics, and high breakdown field, notable of glass, can be obtained. In order to maximize the amount of dielectric material and increase the total energy density of a capacitor, thick film dielectrics have been created from a ceramic-glass slurry that was roller bladed onto Pt coated MgO substrates. BaTiO3 nanoparticles, 50nm in diameter, were dispersed in terpineol and wet milled with crystallizable glass (29.6%BaO- 7.4%SiO- 37%TiO2- 8%SiO2- 16%B2O3- 2%Al2O3) nanopowders using a high energy vibrating ball mill for 4 hrs. The resulting slurry was deposited onto substrates and printed into thick films (25 and 75 µm). Samples were sintered at 1200°C for 4 hrs then crystallized at 1000°C for 2 hrs. Uniform layers of glass-ceramic were observed after heat treatment, characterized by SEM. Pt electrodes were sputtered onto the surface to allow for dielectric characterization. Assuming barium titanate nanoparticles formed close packed structure with the free volume filled with glass, a dielectric constant of 392.3 was expected. Dielectric constant and loss tangent was calculated.

There is enormous focus on the need for materials based on abundant elements, but with a handful of exceptions, few elements are scarce enough for the raw materials cost to be a significant contribution to the product cost. Instead, most materials-supply issues arise from investment-timing issues in the supply-chain. In particular, where there are long lead-times, underinvestment will create a shortage, and the price of the materials may then become a constraint. In photovoltaics, the availability of scarce elements such as In, Ga, and Te has been discussed extensively but the only material the industry ever ran out of was Si. Viewed as a pure supply-chain issue, the long lead-times associated with mineral-extraction stages are especially severe, and are responsible for most of the materials “availability” challenges of the energy industry. This talk will build some typical cost models, and then walk through the impact of time-to-volume and the way that this can alter the overall manufacturing supply-chain and create distorted pricing. This view suggests somewhat different strategies for mitigating shortages as the energy infrastructure is re-invented for the 21st century.

Solar energy collection largely occurs on flat panels in contrast with the 3D strategies adopted in Nature. From rooftop residential installations to modules mounted on sun trackers in large solar farms, the optimization of energy collection is left to the active solar energy adsorbing material in a flat 2D geometry. We propose new tools to optimize the arrangement of solar panels in three dimensions to make macroscopically 3D photovoltaic static devices capable of optimizing the energy generated per base area. 3DPV prototypes show a 100% increase in peak power generation hours, and a measured increase in the energy density by 2-20 times without sun tracking. The increased energy density is countered by a larger solar cell area per generated energy for 3DPV compared to flat panels (by a factor of 1.5-4 in our conditions), but accompanied by a vast range of improvements. 3DPV structures can mitigate some of the variability inherent to solar PV as they provide a more even source of solar energy generation at all latitudes: they can double the number of peak power generation hours and dramatically reduce the seasonal, latitude and weather variations of solar energy generation compared to a flat panel design. Self-supporting 3D shapes can create new schemes for PV installation and the increased energy density can facilitate the use of cheaper thin film materials in area-limited applications. The benefits of 3DPV are applied beyond PV, to include in solar to thermal energy conversion systems.

Inverse opals [1] are a class of self-assembled colloidal structures where material is deposited in the interstices of a colloidal crystal followed by removal of the original template. These structures are promising for applications in photonics [2], solar cells [3, 4] and as anodes in Li-ion batteries [5]. Apart from optical and electrical properties, thermal properties of inverse opals are critical from the perspective of reliability. Here we report the first measurements of the thermal conductivity of polysilicon inverse opals as a function of shell thickness. We fabricate samples with shell thicknesses in the range 18 nm-38 nm and perform transmission electron microscopy and X-ray diffraction to obtain the grain size. We employ the 3omega; method [6] to measure the thermal conductivity as a function of temperature from 15-400 K. During the measurement, a sinusoidal current (at 1omega; frequency) through a metallic heater sets up a 2omega; temperature oscillation, which in turn creates a 3omega; voltage across the metal line. By measuring the 3omega; voltage, the thermal property of the sample material underneath can be extracted. The results show low effective thermal conductivity of the inverse opal structure. For example, the effective thermal conductivity at 38 nm shell thickness is 1.5 W/mK at 300K, two orders of magnitude smaller than bulk silicon. After accounting for porosity, the intrinsic material thermal conductivity is 13 W/mK. We also find that the intrinsic material thermal conductivity is well approximated as that of a thin film with thickness of the shell and average grain size as reported by X-ray diffraction. The effect of shell curvature on thermal transport is inconsequential. 1 J. F. Galisteo-Lopez, M. Ibisate, R. Sapienza, L. S. Froufe-Perez, A. Blanco, and C. Lopez, Advanced Materials 23, 30 (2011). 2 V. L. Colvin, MRS Bulletin 26, 637 (2001). 3 P. Bermel, C. Luo, L. Zeng, L. C. Kimerling, and J. D. Joannopoulos, Opt. Express 15, 16986 (2007). 4 T. Suezaki, J. I. L. Chen, T. Hatayama, T. Fuyuki, and G. A. Ozin, Applied Physics Letters 96, 242102 (2010). 5 Y. Yao, M. T. McDowell, I. Ryu, H. Wu, N. Liu, L. Hu, W. D. Nix, and Y. Cui, Nano Letters 11, 2949 (2011). 6 D. G. Cahill, Review of Scientific Instruments, 61, no. 2, pp. 802-808 (1990).

Abstract In general, a large number of perovskite oxides show various promising physical properties such as semiconducting, superconducting, ionic conducting, ferroelectric, and ferromagnetic properties [1]. Recently, we have found ML properties in Sm3+ doped Srn+1SnnO3n+1 (n = 1, 2, infin;) phosphors, which consist of stacked perovskite monolayers (n = 1; lattice parameter a = 5.735, b = 5.729, c = 12.587 Å, space group Pccn), double layers (n = 2; a = 5.710, b = 5.736, c = 20.688 Å, space group Amam), and the ordinary perovskite structure (n = infin;; a = 5.709, b = 5.703, c = 8.065 Å, space group Pbnm), exhibited ML. Here mechanoluminescence (ML) is a phenomenon where photons are emitted by mechanical stimuli; it is of particular interest for use in stress sensing devices which detect damage, fracture, and deformation in various structures. Interestingly, ML intensity for Srn+1SnnO3n+1:Sm3+ (n=1, 2, infin;) were altered by the intra-layer configuration; the ML intensity for Sr3Sn2O7:Sm3+ was five orders of magnitude higher than that for SrSnO3:Sm3+. This observed ML phenomenon can be understood on the basis of the carrier trap model, for which an electron and/or a hole trapped in a lattice defect such as a point defect, an co-doped ion, and others, is released by a mechanical stimulus and it is recombined at luminescence center, thus emitting a light [2]. In the case of Srn+1SnnO3n+1:Sm3+ (n=1, 2, infin;), supposing that Sm3+ ions are incorporated into Sr sites, two point defects of the Sm impurity (SmSr) and the Sr vacancy (V"Sr) were created in the host lattice due to charge compensation. Furthermore, the charge transfer state band in the photoluminescence excitation spectra was observed for Sr3Sn2O7:Sm3+ and Sr2SnO4:Sm3+, indicating that the efficient energy transfer from the host to the Sm3+ ions. The ML and the related optical properties of Srn+1SnnO3n+1:Sm3+ (n=1, 2, infin;) were investigated and the ML enhancement process was discussed. Reference [1] F. S. Galasso, Structure, Properties and Preparation of Perovskite-type compounds (Pergamon, Oxford). [2] C. N. Xu, T. Watabe, and M. Akiyama, and X. G. Zheng, Appl. Phys. Lett., 74, 2414 (1999).

Phosphor-converted light emitting diodes have become a very promising method for efficient generation of white light. Many benefits are offered over traditional incandescent and fluorescent lamps including longer device lifetimes and reduced energy consumption, without the need for mercury. The phosphor material is a crucial component of these devices and can dictate the overall color properties of the white light. Current solid state white lighting devices comprise a blue LED coupled with a yellow- and/or red-emitting phosphor. The addition of a red-emitting phosphor provides improvements in the color properties, leading to warm white light with high color rendering, but can also hinder the efficiency of the device by adding another conversion component. The phosphors must therefore be highly efficient with weak thermal quenching, the latter of which is a significant problem in red-emitting phosphors. Oxynitride materials have thus gained interest for this purpose as being efficient, stable, red-emitting phosphors. Oxynitrides of the family M-Si-O-N, where M is a trivalent cation, are promising host materials for red-emitting phosphors. The introduction of N3+ into the lattice is crucial in creating a more polarizable environment around the activator ion compared to a solely oxide host. This lowers the excited state of the activator ion due to a large crystal field splitting and strong nephalauxetic effect, resulting in red-shifted emission. The local structure around the activator ion is therefore extremely important in dictating optical properties of the phosphor. The structures of these M-Si-O-N materials (M= Lu3+, Y3+, La3+) with Ce3+ as an activator ion have been studied along with their photoluminescent properties, temperature stability, and device characteristics.

Phosphor-converted white light-emitting diodes (LEDs) have long been expected to replace the conventional lighting sources for indoor illumination. Due to the lack of a sufficient red spectral component in the emission spectra of the commonly used yellow emitting phosphors (e.g., market dominating YAG:Ce3+), however, the current white LEDs generally emit a cool, bluish-white light, which are undesirable for indoor use. For indoor lighting, the white light should be warm-white (i.e., correlated color temperature (CCT) <4000 K) with sufficient color rendition (i.e., color rendering index (CRI) >80). No single-phosphor, single-emitting-center-converted white LEDs can simultaneously satisfy these color temperature and rendition requirements. Recently, we synthesized a new yellow barium europium aluminate (BEAO) phosphors that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component from a single Eu2+ emitting center. Warm-white emissions with CCT <4000 K and CRI >80 can be readily achieved when combining the BEAO phosphor with a blue LED (440minus;470 nm). This study demonstrates that warm-white LEDs with high color rendition (CRI >80) can be achieved based on single-phosphor, single-emitting-center-conversion. Moreover, the material contains nanowire structures and was synthesized by a thermal evaporation-based technique, which is new for luminescent material synthesis. Therefore, our study opens a new avenue for the discovery and fabrication of novel luminescent materials for white LEDs and other advanced photonic applications.

Fluorescent SiC is a novel materials system which may become a new platform for visible and infrared emitting applications. Although SiC is an indirect bandgap semiconductor, efficient donor acceptor pair emissions involving deep acceptors are possible if the acceptor envelope functions are sufficiently localized. Nitrogen and boron co-doped SiC exhibits a highly efficient donor acceptor pair emission at room temperature [1] and can be applies as a rare earth metal free white LED for general lighting [2]. Such donor acceptor pair emission provides broad emission bands in the wavelength ranging from visible to infrared region depending on the SiC polytype. In 6H-SiC the emission appears in the visible range from 500 to 700 nm with a peak at 580 nm, appearing as a warm white color, while 4H yields an emission band in the green region from 450 to 650 nm with a peak at 520 nm. The 3C-SiC polytype has a lower bandgap than its hexagonal counterparts which results in an emission in the infrared region from 700 to 900 nm with a peak at 830 nm. Further on, replacing the deep acceptor boron with the shallow acceptor aluminum would open up new emissions at shorter wavelengths still in the visible and infrared regions and hereby allow tuning of the emission wavelength for desired purposes. The combination of the polytypes covers a broad range of emission in the visible and infrared region, and the fluorescent SiC can act as a base material for SiC based light emitting materials having benefits from the SiC properties such as chemical stability, high thermal conductivity and lattice matching with nitride growth for LED fabrication. In addition, the 3C-SiC is a potential solar cell material. For boron doped cubic SiC, the dopant band of B in the bandgap of 3C-SiC leads to a efficient use of sun light so that an efficiency up to 48-60% could be achieved depending on the theoretical model [3,4]. To demonstrate such high efficiency, one requirement is high material quality to have efficient optoelectronic transitions. We have shown that 3C-SiC could be grown in a very high quality [5,6]. Carrier lifetime is the other key parameter governing the efficiency of electronic and optoelectronic devices. Very recently we have synthesized high quality 3C-SiC by a PVT process on 6H-SiC with a very high growth rate of 1 mm per hour. The carrier lifetime is 8.2 mu;s, and surprisingly this is even higher than that in as-grown 4H-SiC. Such material paves the way to explore cubic SiC for photovoltaics. [1] J. Appl. Phys. 99 (2006) 093108. [2] J. Semiconductors 32 (2011) 13004. [3] Prog. Photovolt. Res. Appl. 10 (2002) 345. [4] Phys. Rev. Lett. 78 (1997) 5014. [5] Appl. Phys.100 (2012) 252101. [6] Adv. Mat. Lett. 3 (2012) 175.

The crystal structure and photoluminescent (PL) properties of the oxyfluoride NaCa₂GeO₄F^[1] and its related compounds have been studied. Analysis of X-ray powder diffraction data has shown that NaCa₂GeO₄F is a hexagonal antiperovskite and it possess an anion ordered structure containing closely packed BX₆ face-sharing octahedra, where B is the anion (fluoride) and X is the cation (Na/Ca).^[1] NaCa₂GeO₄F, has an orthorhombic unit cell with lattice parameters, a = 5.3665(2) Å, b = 7.3270(5) Å, c =12.6871(6) Å, V = 498.72(8) ų, space group Pnma (No. 62), Z = 4. These compounds are proven to be stable in air and humidity by examining the XRD patterns of freshly prepared sample and of samples more than a month old. Except from negligible amount of lattice expansion in old material no significant change was found. Photoluminescent data of stoichiometric NaCa₂GeO₄F shows self-activating luminescence at 254 nm and 365 nm UV excitation due to the presence of disorder in FM₆ (M = Na/Ca) octahedra and GeO₄ tetrahedra. The materials are prepared by mixing CaCO₃, GeO₂ and NaF and heating at 850-950 °C using solid state reaction method under N₂ flow. Ba²⁺ was substituted for Ca²⁺ and the compounds in the NaCa_2-xBa_xGeO₄F (x = 0.01, 0.015, 0.02, 0.025, 0.035, 0.04, 0.045) series prepared under reducing environment (95% Ar/5% H₂) are self activating. These materials exhibit slight yellow luminescence under 254 nm UV light and broad emission band in 500-620 nm range at 365 nm excitation. There are distinct crystallographic sites for the cations are present in the structure which can be occupied with suitable rare earth dopants. The PL data of Ce³⁺ doped Na_1+xCa_2-2xCe_xGeO₄F, Na_1+yCa_2-x-2yBa_xCe_yGeO₄F and Eu²⁺ doped with Ce³⁺ codoped Na_1+yCa_2-x-2yEu_xCe_yGeO₄F materials exhibit excitation peaks in the 360 to 465 nm range. The results show that these compounds have potential to be used as n-UV phosphor for LED.^[2,3,4] Eu³⁺, Tb³⁺ and Mn²⁺ with Ce³⁺ as sensitizer were also substituted in NaCa₂GeO₄F host lattice and photoluminescent properties were examined. The CIE values for different PL results and structural analysis report using Rietveld refinement of X-ray powder diffraction data are presented. References (1) Schneemeyer, L. F.; Guterman, L.; Siegrist, T.; Kowach, G. R. J. Solid State Chem. 2001, 160, 33-38. (2) Park, S.; Vogt, T.; J. Phys. Chem. C2010, 114, 11576-11583. (3) Woodward, P. M.; Acta Cryst. 1997, B53, 32-43. (4) Glaser, E. R.; Kennedy, T. A.; Carlos, W. E.; Ruden, P. P.; Nakamura, S.; Appl. Phys. Lett., 1998, 73 (21), 3123.

Efforts are being continuously made to improve status of current gallium nitride on sapphire based solid state lighting to enable acceptance of this technology for mainstream house-hold lighting by reducing cost of brighter LED bulbs. Amongst the methods being explored, presence of aluminum nitride (AlN) nucleation layer and use of patterned sapphire substrates are touted as some major advances in the technology to improve, the external as well as internal quantum efficiencies of GaN based SSL technology. AlN based buffer layer is also likely to play an important role in the realization of GaN on silicon and possibly on glass technology. Hence, it is important to understand the microstructure of AlN epitaxial layers. Amongst various methods for deposition, wide spread physical vapor deposition (PVD) technique like reactive sputtering that enable comparatively faster growth rates and low cost of ownership may be preferred. Asymmetric (10L) XRD peaks have been employed as a measure of epitaxial quality for aluminum nitride (AlN) nucleation layers (NL) deposited on sapphire substrate. Epitaxial AlN films have been deposited on sapphire substrate by reactive sputtering. FWHM of AlN (103) and (105) were found to be an excellent indicator of quality of AlN films for GaN growth. AlN films produced nucleation layers with highly reproducible microstructure and GaN film growth. NLs had in-plane and out-of-plane texture as evident by the pole-figure results and selected area diffraction pattern. Based on electron microscopy results, AlN film thickness for complete atomic ordering was estimated to be 6-7 nm and most of the edge dislocations were seen in the first 20 nm of the film. Excellent thickness and texture uniformity were seen on 4 inch planar sapphire substrates. The lattice parameters for wurtzite AlN, estimated from symmetric (00L) and asymmetric (10L), were found to be 3.077 ± 0.004 Å (a) and 5.005 Å ± 0.002 Å (c). A compressive stress of 2.9±0.2 GPa was seen in our BKM films. The maximum screw and edge dislocation densities of films were found to be ~3 x 108 cm-2 and ~9 x 109 cm-2 respectively. The root mean square roughnesses of A-polar films were found to be ~0.3 nm. Films were also uniformly coated on 4” and 2” patterned sapphire substrates

The bandgap of GaN is widely tunable in the ultraviolet and visible ranges by alloying with AlN and InN. With reliable p- and n-type doping capability and high internal quantum efficiency, GaN has been widely used for commercial blue and green light-emitting diodes (LEDs). Conventional GaN LEDs are fabricated by metalorganic chemical vapor deposition (MOCVD) on expensive single-crystalline sapphire substrate that is limited in size. Recently, there are progresses in the field of fabrication GaN on large (150mm and 200mm) silicon wafers to overcome the size limitation of sapphire wafers. However, silicon substrate has a large thermal expansion mismatch with GaN and the induced strains cause cracking and wafer bowing. Furthermore, silicon is nontransparent in the visible spectrum thus a complicated and challenging substrate removal and GaN film transfer process is necessary to fabricate efficient LEDs. In this work, we demonstrate a novel way of fabricating GaN LED array on SiO2 /Si (100) substrate by MOCVD. C-direction orientated high temperature AlN seeding layer is grown directly amorphous SiO2 and single crystalline hexagonal GaN pyramid LEDs is achieved on the AlN seeding through a patterned SiO2 mask by means of local area epitaxy. Since individual GaN pyramids is physically disconnected, the entire wafer shows no cracking or bowing. Finally an array of GaN pyramid LEDs is fabricated and lift-off by a convenient wet-etch of the bottom SiO2 layer. The advantages of GaN pyramid arrays in high crystalline quality and high light extraction geometry is fully examined in comparison with a conventional planner GaN LED on sapphire by electroluminescence measurement.

With power module technology rapidly advancing toward higher voltage and greater power density, requirements for heat dissipating ceramic substrates used for power modules are getting higher. For such applications as insulating substrates, silicon nitride (Si3N4) is regarded as one of the leading candidate materials, because its mechanical strength is outstanding among major structural ceramics and the intrinsic thermal conductivity of a Si3N4 single crystal has been reported to exceed 200 W/(mK). However, thermal conductivities of polycrystalline silicon nitride ceramics are much lower. Oxygen impurity dissolved in the lattice of Si3N4 grains has been regarded as the dominant factor lowering the thermal conductivity of Si3N4 ceramics. Here, we report the preparation of Si3N4 ceramics via a route of sintering of reaction-bonded silicon nitride (SRBSN), where green compacts composed of a high purity silicon powder and a small amount of sintering additives were firstly nitrided in a nitrogen atmosphere and then sintered at higher temperatures to attain full densification. By optimizing the nitridation conditions, minimizing the lattice oxygen content and appropriately enhancing grain growth during the post-sintering process, Si3N4 ceramics possessing thermal conductivities as high as 177 W/(mK) along with rather high fracture toughness and strength could be fabricated. These high thermal conductivity Si3N4 ceramics are expected to be used as the substrate materials for the next-generation power modules.

A Pt-group metal (PGM) free catalytic reactor has been successfully fabricated by incorporating hierarchically three dimensional (3-D) Co3O4 nanoarrays into monolithic honeycomb with a facile one pot synthetic strategy. The precursor variation has led to formation of various 3-D Co3O4 nanostructures with different sizes and shapes. These Co3O4 nanoreactors exhibit remarkably high conversion efficiency for catalytic NO oxidation up to 90% at high space velocity (~55000/h) but relatively low temperature. These reactors boast a ~50g/L of cobalt oxide loading as the PGM free catalyst, less than those of traditional honeycomb supported Al2O3/PGM catalysts. Detailed characterization of grain size, surface area, pore size as well as surface condition suggests that size and Co3+ ions determine the catalytic activity of the nanoreactors. These nanoreactors maintain high efficiency during cyclic catalytic tests, with negligible catalytic activity degradation after long term and temperature fluctuation tests. The ultra-efficient but cost-effective nanoreactor for NO oxidation could serve as a good candidate device in environmental applications such as automobile and industrial exhaust after-treatment, where higher NO conversion into NO2 could tremendously increase the efficiency of advanced NOx removal technologies such as selected catalytic reduction (SCR) or NOx storage and reduction (NSR). References: 1)Z. Ren, Y. Guo, Z. Zhang, C. Liu, P.X. Gao, “Ultra-efficient Catalytic Nanoreactor Structured with Hierarchically Three Dimensional Co3O4 Nanoarrays for High Performance NO Oxidation,” in preparation. 2)Kim, C. H., Qi, G., Dahlberg, K. & Li, W. Strontium-doped perovskites rival platinum catalysts for treating NOx in simulated diesel exhaust. Science 327, 1624-1627, (2010). 3)Boger, T., Heibel, A. K. & Sorensen, C. M. Monolithic catalysts for the chemical industry. Ind. Eng. Chem. Res. 43, 4602-4611, (2004).

Molecular level interactions at organic-inorganic interfaces play a crucial role in many fields including materials synthesis, drug delivery, and also possibly mineral precipitation in presence of organic matter. To seek insight into organic-inorganic interactions in porous framework materials, we investigated the phase evolution and energetics of confinement of rigid organic guest TMAAI (N,N,N-trimethyl-1-adamantammonium iodide) in mesoporous silica frameworks (MCM-41 and SBA-15) as a function of pore size (2.2 nm to 20.0 nm). We used HF solution calorimetry (25% HF aqueous solution, at 50 oC) to obtain the enthalpies of interaction between mesoporous silica framework materials and TMAAI and the values range from -35 to -120 kJ/mol of TMAAI. Phase evolution was investigated by XRD, IR, TG-DSC and solid-state NMR. The results suggest the existence of three types of interactions depending on the pore size of frameworks: single-molecule confinement, multi-molecule confinement/adsorption and nanocrystal confinement. Single molecule confinement occurs when TMAAI molecule is tightly surrounded by the silica wall due to close geometric fit of TMAAI to the pore. For the same organic molecule, when the pore size of the framework increases, the system tends to stabilize by re-arranging TMAAI molecules as an adsorbed mono-layer or multi-layers on the pore walls. Once the pore size becomes large enough to allow the formation of at least a single unit cell of the TMAAI crystal, the crystallization of TMAAI molecules into nanocrystals is observed and may further stabilize the system. The observed melting point of such crystals depends on their size which in turn is controlled by the size of the pore.

The discovery of efficient photo-catalysts is one of the grand challenges for energy conversion and storage. Naturally occurring materials do not fulfill all the required electronic criteria for any given energy conversion process. These electronic requirements in materials are usually targeted by a band-engineering approach, where the electronic structures of the materials are engineered by selective doping. However, the introduction of impurities would create unwanted defect states in band gap, which would be detrimental to the transport properties of the host due to poor crystallinity. In general, shifting the optical absorption spectrum of a material to the visible region by doping-only process has not been successful in improving the photoconversion efficiency significantly. Here, instead of following a conventional band engineering approach, we would follow novel alloys design approach by following mineral database search methods. Our recent results on some complex multi-cation oxide materials for potential photocatalysts will be presented. We will use density functional theory (DFT) to determine their lowest energy crystal structures and study their electronic properties.

In the drive to produce efficient catalytic emission control devices while minimizing the use of noble metals, strontium-doped perovskite-type materials have become of interest lately [1], [2]. These materials may soon lead to a new generation of aftertreatment catalysts for carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in diesel and gasoline engine exhaust. In this study, ZnO/(La,Sr)CoO3 composite nanorod arrays have been grown in cordierite honeycomb substrates, providing high surface area, efficient materials loading and drastically reduced materials usage, and enhanced chemical and thermal stability. With this process, one could create a low cost nanocatalyst with superior performance for diesel oxidation (DOC) and lean NOx trapping (LNT). A comparative investigation of preparation methods has been carried out on this materials system. The relationships have been unraveled in this investigation between the structure and morphology of the ZnO/(La,Sr)CoO3 and the catalytic properties of the enabled catalytic devices. This new type of nano-array catalyst could be a good candidate for low-temperature combustion engine exhaust aftertreatment catalysis. References: 1. C.H. Kim, G. Qi, K. Dahlberg and W. Li, Science 26, 1624-1627 (2010). 2. D. Jian, P.X. Gao, W. Cai, B.S. Allimi, S.P. Alpay, Y. Ding, Z.L. Wang and C. Brooks, J. Mater. Chem. 19, 970-975 (2009).

The Solar Thermal Electrochemical Production of energetic molecules converts solar energy at high efficiency. Rather than electricity, a variety of useful chemicals, including solar fuels and iron without CO2 emission, are produced by this STEP process. A synergy of solar thermal and solar-electric and other renewable energy electronic charge transfer, forms an alternative higher efficiency solar energy conversion process. For example, STEP can split CO2 with >50% solar efficiency. The STEP approach for solar energy conversion is based on our theory and experimental observation that even a semiconductor with bandgap smaller than the water splitting potential (E(H2O)=1.23V at 25°C) can split water at elevated temperature [1]. Hence, silicon (band-gap 1.1 eV) was used to directly form hydrogen fuel from water at elevated temperature in a novel molten alkali hydroxide electrolyzer. STEP generalizes the advantage of this energy conversion process to the endothermic formation of all useful, energetic molecules, is and includes STEP cost effective production of hydrogen, iron fuels, bleach and carbon capture [2] and cement [3]. The STEP process distinguishes sunlight that is energy sufficient to drive photovoltaic charge transfer, and applies solar thermal energy to heat and decrease the energy of enodothermic electrolysis reactions. This process captures sunlight with conversion efficiency greater than either photovoltaic or solar thermal electric processes, through the use of the global (visible + thermal) sunlight. Energy sufficient, visible, sunlight drives photovoltaic charge transfer, and available heat, infrared sunlight, and excess visible sunlight, heats, and decreases the energy of, an electrolysis reaction. In the STEP process, rather than electrical generation, solar energy directly provides the chemical products needed by society. This original process is derived for the solar generation of energetically rich chemicals, including chlorine, metals, hydrogen and to proactively convert anthropogenic CO2 generated in burning fossil fuels towards the formation of energy rich hydrocarbons, including solar synthetic diesel. As one STEP example, carbon dioxide is inherently highly stable and noncombustible. This thermodynamic stability creates a very high activation energy, until now, the process of efficient CO2 conversion had been considered a difficult, if not impossible, task [5]. However, STEP conversion can recycle and remove CO2 at ampere level currents and high solar efficiency [2]. References 1. S. Licht, STEP: A solar chemical process to end anthropogenic global warming, J. Phys. Chem., C, 2009, 113, 16283. 2. S. Licht, Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Solar Thermal Electrochemical Production of Fuels, Metals, Bleach, Adv. Mat. 2011, 47, 5592. 3. S. Licht, B. Wang STEP Cement: Solar Thermal Electrochemical Production of CaO without CO2 emission, Chem. Comm. 2012, 48, 6019.

Two-step solar-driven thermochemical water splitting is a highly attractive technology for solar fuels production. The thermochemical approach provides the advantage of full utilization of solar spectrum and does not require precious metal catalysts. The process is essentially that of a heat engine, in which oxygen is released from the catalytic oxide at a high temperature and hydrogen is released at a low temperature due to the re-oxidation of the solid by water vapor. Our laboratory has demonstrated the effectiveness of the non-stoichiometric oxide, CeO2-δ for this process and shown that materials with even moderate changes in oxidation state have the potential for high efficiency solar fuel production. However, ceria requires extreme temperatures to induce oxygen release, placing high demands on reactor construction and negatively impacting system efficiency. The pervoskite structure, like fluorite, can support a high concentration of oxygen vacancies. In addition, the structure is highly flexible in that a broad range of cations can be incorporated in to the A and B sites, creating the possibility for tuning properties. Here, we examine, in particular, the La1-xSrxMnyFe1-yO3 (LSMF) system and find that the system displays both attractive thermodynamics and kinetics for hydrogen production at reduced temperatures relative to those required for ceria. On cycling between 800 and 1400 °C, hydrogen production as high as 5.3 mL/g was obtained (exceeding that of ceria under comparable conditions), with no obvious degradation over the course of 9 cycles. Moreover, the light absorbance of LSMF is about 80-90% in a wide wavelength range of 250-2500 nm, suggesting high utilization of the solar spectrum. Further compositional tuning to minimize the lanthanum content in LSMF may lead to an earth-abundant catalytic oxide for thermochemical water splitting. The link between the solid-state chemistry, redox properties, and hydrogen production will be discussed.

In the pursuit to find a practical system for hydrogen storage, complex metal hydrides have long been considered as viable candidates due to their high hydrogen content. However, some of the challenges faced with these types of systems are poor thermodynamics or kinetics, and thus the underlying mechanisms, and their limiting processes, for the decomposition of these materials need to be understood. From experimental work on the decomposition of hydrogen storage materials, it has been suggested that bulk diffusion of metal species is the bottleneck for hydrogen release. The two systems that are investigated in this work is the dehydrogenation of LiNH2 + LiH, with favorable hydrogen release (7.0 wt %) and LiAlH4→LiAlH6 (5.3 wt %), both at moderate temperatures. Using first-principles density functional theory we found the defects facilitating mass transport by calculating individual formation energies, highest concentrations, and activation barriers for defect mobility. The results are used to further our understanding of the fundamental mechanism of mass transport and evaluate the possibility of kinetics as the limiting process for these two hydrogen storage reactions.

Hydrogen was converted to such a material as coal or oil with a low specific gravity so that it could be stored for a longer period and transported for a long distance at room temperature and under atmospheric pressure; which is sodium. Sodium is produced with molten-salt electrolysis from seawater by wind or solar power and transported to a thermoelectric power station in the consumption place for hydrogen-fueled combustion power generation. Coal and oil have reigned in fossil fuel because they can be kept well for long and transported for long; however, their reserve production ratios are limited. Salt, which is the raw material of sodium, exists evenly in the world: as seawater in the sea and rock salt or saline lake on the Continents. There is no worry about maldistribution and exhaustion of resources. Coal and oil discharge CO2 when burnt, but hydrogen does not discharge CO2 and is a clean, environmentally friendly fuel. Hydrogen itself is light, but the gas cylinder and absorption alloy for storage are very heavy and unsuitable for transportation. If possible to solidify it at room temperature under atmospheric pressure, hydrogen can be stored for long and transported for long. In general, molten salt electrolysis is the only method to produce sodium from sa< which needs high power, being very expensive. To reduce the production cost, therefore, there should be no industrial wastes but high value added by-products in processing, bearing “zero emission” in mind. And, a sodium production plant is constructed in the sea as a material supply location, where renewable energy obtained on site is used to generate electricity for its operation. In the process of manufacturing sodium and generating hydrogen, fresh water, sulfuric acid, hydrochloric acid, sodium hydroxide, and magnesium are produced as by-products. The by-products are the things that have consumed a large amount of electricity for production; which themselves are paying, and the economical efficiency is high. Moreover, the production site is conveniently located on the raw material, seawater or rock salt, and the power plant is operated by natural energy resources such as wind and photovoltaic power. The economic benefit is enormous overall. Natural energy resources such as wind power and solar power are influenced by weather, and the net generation is not constant. If the natural energies are converted to some fuel, the uncertainness of the weather can be disregarded, and the long-term storage and long-distance transportation will be possible. It is considered here to convert hydrogen into sodium. The sodium is produced by molten-salt electrolysis of seawater salt or rock salt and is securely stored in kerosene to transport to a consumption place; a large amount of hydrogen is generated instantaneously anywhere when adding water on the sodium. And sodium hydroxide, the waste, is provided to the soda industry.

Ceria is the most important rare-earth element because of its redox behavior and oxygen storage capacity (OSC). Experimental and theoretical studies reveal surface and structure-dependent reactivity of ceria nanostructures. Herein, we synthesize CeO₂ nanorods, nanocubes, nano-octahedra with dominant (110) + (100), (100) and (111) reactive surfaces respectively. Catalytic activity measurement with these nanostructures reveal the influence of the various reactive facets on the activity. We adopt an ultrafast, microwave-assisted route to attach capping-free, ultrafine platinum nanoparticle on the ceria polyhedra. Under the same synthesis conditions, the size of the Pt nanoparticles on different facets vary, clearly revealing the difference in the efficacy for promoting heterogeneous nucleation. These heterojunction based nanostructures are found to be promising catalysts for CO oxidation even at low temperatures. We have studied in detail the role of process parameters, particle size and the surface oxygen reducibility of ceria on the catalytic activity. Activation energy calculation confirms CeO₂ / Pt nanohybrids with CeO₂ nanorods as support, the preferential candidate for catalysis. Detailed structural characterization of these nanohybrids were carried out using X-Ray Diffraction (XRD), X-Ray Photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), BET specific surface area analysis. IR-spectroscopy and UV-Raman spectroscopy measurements provide essential information about the CO adsorption on the surface and its interaction with the lattice oxygen resulting the formation of different species on the surface.