111th MSL Lecture (Professor James Neilson) 10/25
Enabling Prescriptive Synthesis of Metastable Ternary Oxides with Mixed Anions
Complex oxides enable a diverse set of electronic properties. However, we do not yet know how to prescriptively synthesize desired compositions or polymorphs of materials, particularly if they are metastable. Metathesis (or double-exchange) reactions are well suited to address synthesis questions pertaining to atomic transport and permit the identification of incipient stages of phase differentiation in solid-state reactions. As an example, the reaction, A2CO3 + Mn2O3 + YCl3, where A = Li, Na, or K, yields different Y-Mn-O products (and polymorphs) depending on which spectating alkali is present. From a combination of in situ and ex situ analysis of myriad synthesis reactions combined with first-principles calculation of thermodynamic parameters, we identify competent intermediates that enable kinetic control of the reaction, such as the phases LiMnO2 and YOCl. These results allow us to establish the critical processes in solid-state reaction pathways that enable, or hinder, prescriptive synthesis.
Paul K. Todd and James R. Neilson, J. Am. Chem. Soc. 141, 1191-1195 (2019)