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.

中文翻译：

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层状氧化物固态合成中热力学和动力学之间的相互作用。

在合成无机材料时，反应通常会产生非平衡动力学副产物，而不是热力学平衡相。了解热力学和动力学之间的竞争是目标材料合理合成的基本步骤。在这里，我们使用原位同步加速器X射线衍射研究重要的两层（P2）氧化钠Na0.67MO2（M = Co，Mn）的多级结晶途径。我们观察到在形成平衡的两层P2多晶型物之前，通过亚稳的三层O3，O3'和P3相进行了一系列快速的非平衡相变。我们提供了一个理论框架来合理化观察到的相变，表明即使P2是平衡相，粉末前体之间的成分不受约束的反应有助于形成非平衡的三层中间体。这些见解可以指导陶瓷材料固态合成中使用的前驱物和参数的选择，并为揭示材料合成过程中热力学和动力学之间的复杂相互作用迈出了一步。