David Carriere1
CEA1
Crystallization from solution often involves transient, non-crystalline states like reactant-rich liquid droplets and amorphous particles [1]. This state of affairs not only challenges the chemical engineering models used to rationalize laboratory- and industrial-scale processes, but also motivates deep experimental tests of the multistep nucleation theory proposed as an alternative to the well-known classical nucleation theory of Becker and Doering [2]. However, testing both engineering and physical models requires challenging quantification of the structures and phases (sizes, volume fractions, crystallinity, compositions), down to the millisecond reaction times and sub-nanometer characteristic lengths.<br/><br/>Here, I will illustrate how coupling synchrotron X-ray methods and electron microscopy can tackle challenging scientific questions in the crystallization of oxide nanoparticles, vanadates and rare-earth oxalates through: 1) providing evidence of transient structures, and sometimes multiple transient structures, together with growing crystals [3–6] 2) assessing the impact of these transient phases on the final product, in particular when it consists of nanometer-sized aggregates of nanocrystals [5] 3) providing evidence of an evolution in the chemical composition of the transient phases [6] and 4) assessing the impact of the transient phases on chemical engineering models [7].<br/><br/><b>References</b><br/>1. Yoreo, J. J. D. <i>et al.</i> Crystallization by particle attachment in synthetic, biogenic, and geologic environments. <i>Science </i>349, aaa6760 (2015).<br/>2. Vekilov, P. G. Nonclassical Nucleation. in <i>ACS Symposium Series</i> (ed. Zhang, X.) vol. 1358 19–46 (2020).<br/>3. Fleury, B. et al. Amorphous to Crystal Conversion as a Mechanism Governing the Structure of Luminescent YVO4:Eu Nanoparticles. <i>ACS Nano</i> 8, 2602–2608 (2014).<br/>4. Baumgartner, J. <i>et al.</i> Self-Confined Nucleation of Iron Oxide Nanoparticles in a Nanostructured Amorphous Precursor. <i>Nano Lett.</i> 20, 5001–5007 (2020).<br/>5. Freitas, A. P. <i>et al.</i> Crystallization within Intermediate Amorphous Phases Determines the Polycrystallinity of Nanoparticles from Coprecipitation. <i>Nano Lett.</i> 22, 29–35 (2021).<br/>6. Durelle, M. <i>et al</i>. Coexistence of Transient Liquid Droplets and Amorphous Solid Particles in Nonclassical Crystallization of Cerium Oxalate. <i>J. Phys. Chem. Lett.</i> 13, 8502–8508 (2022).<br/>7. Durelle, M. <i>et al.</i> Measurement of Nucleation Rates during Nonclassical Nucleation of Cerium Oxalate: Comparison of Incubation-Quenching and In Situ X-ray Scattering <i>Crystal Growth & Design</i> (2023)