The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides

Matteo Bianchini+, Jingyang Wang+, Raphaële J. Clément, Bin Ouyang, Penghao Xiao, Daniil Kitchaev, Tan Shi, Yaqian Zhang, Yan Wang, Haegyeom Kim, Mingjian Zhang, Jianming Bai, Feng Wang, Wenhao Sun*, Gerbrand Ceder*

Nature Materials volume 19, pages1088–1095 (2020)

In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na0.67MO2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3′ and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis.