No abstract

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 fundamental 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 Na 0.67 MO 2 (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 favor the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solidstate synthesis of ceramic materials, and constitutes a step forward in unraveling the complex interplay between thermodynamics and kinetics during materials synthesis.