Using Neutron Scattering to Reveal Complex Dynamics of Ions in Energy Materials

A better understanding of atomic motions in solids is critical to design improved materials for a wide range of energy applications. Neutron scattering provides us with key insights into a wide range of atomic dynamics in solids, from fast ionic diffusion in solid-state electrolytes to phonon propagation and thermal transport in thermoelectrics, or electron-phonon coupling and phase transitions in metal-halide perovskites for photovoltaics and optoelectronics. Our group combines state-of-the-art neutron and x-ray scattering techniques together with atomistic materials modeling to probe and rationalize atomic dynamics. This presentation will highlight results from our investigations of atomic dynamics in several classes of materials impacted by strong anharmonicity and a proximity to lattice instabilities, such as halide perovskite photovoltaics, thermoelectrics, and superionic conductors [1-6]. In these materials, we have found that one needs to properly account for the effect of strong anharmonicity, which disrupts the quasiharmonic phonon gas model through large phonon-phonon coupling terms. Large phonon amplitudes can also amplify the electron-phonon interaction and lead to renormalization of a material’s electronic structure. Similarly, phonons of the host framework couple with hopping of mobile ions in superionic conductors, and significantly impact the bulk diffusivity. Such interactions, often neglected in textbooks, remain insufficiently understood but could open the door to new and improved material functionalities. By mapping spatio-temporal correlations throughout reciprocal space, complex atomic dynamics can be studied in detail. Our first-principles simulations enable the quantitative rationalization of these effects, for example with ab-initio molecular dynamics simulations and machine-learning accelerated simulations. <br/> <br/>[1] T. Lanigan-Atkins^*, X. He^*, M. J. Krogstad, D. M. Pajerowski, D. L. Abernathy, Guangyong NMN Xu, Zhijun Xu, D.-Y. Chung, M. G. Kanatzidis, S. Rosenkranz, R. Osborn, and O. Delaire, “<b>Two-dimensional overdamped fluctuations of soft perovskite lattice in CsPbBr₃</b>”, Nature Materials (2021), https://doi.org/10.1038/s41563-021-00947-y<br/>[2] J. Ding, T. Lanigan-Atkins, M. Calderon-Cueva, A. Banerjee, D. L. Abernathy, A. Said, A. Zevalkink, and O. Delaire, “<b>Anharmonic phonons and origin of ultralow thermal conductivity in Mg₃Sb₂ and Mg₃Bi₂</b>”, Science Advances (<i>2021)</i><br/>[3] T. Lanigan-Atkins*, S. Yang*, J. L. Niedziela, D. Bansal, A. F. May, A. A. Puretzky, J.Y.Y. Lin, D. Pajerowski, T. Hong, S. Chi, G. Ehlers, and O.Delaire. "<b>Extended anharmonic collapse of phonon dispersions in SnS and SnSe</b>", Nature Communications 11 (1), 1-9 (2020). https://doi.org/10.1038/s41467-020-18121-4 <br/>[4] J. L. Niedziela, D. Bansal, A. F. May, J. Ding, T. Lanigan-Atkins, G. Ehlers, D. L. Abernathy, A. Said & O. Delaire, “<b>Selective Breakdown of Phonon Quasiparticles across Superionic Transition in CuCrSe₂</b>”, Nature Physics, 15, 73–78 (2019). https://doi.org/10.1038/s41567-018-0298-2<br/>[5] M. K. Gupta, J. Ding, N. C. Osti, D. L. Abernathy, W. Arnold, Hui Wang, Z. Hood and O. Delaire, “<b>Fast Na diffusion and anharmonic phonon dynamics in superionic Na₃PS₄</b>”, Energy and Environmental Science (2021), https://doi.org/10.1039/D1EE01509E<br/>[6] M. K. Gupta, J. Ding, D. Bansal, D. L. Abernathy, G. Ehlers, N. C. Osti, W. G. Zeier, O. Delaire, “<b>Strongly Anharmonic Phonons and Their Role in Superionic Diffusion and Ultralow Thermal Conductivity of Cu7PSe6</b>”, Advanced Energy Materials 12, 2200596 (2022),<br/>https://doi.org/10.1002/aenm.202200596