Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523-1872 , United States.
J Am Chem Soc. 2019 Jan 23;141(3):1191-1195. doi: 10.1021/jacs.8b10123. Epub 2019 Jan 11.
The synthesis of complex oxides requires high temperatures to overcome barriers imparted by solid-state diffusion; as such, reactions typically yield the most stable polymorph for a given composition. To synthesize new or metastable complex oxides, kinetically competent reactions with lower initial energy barriers must be devised to control the reaction pathway and resulting products. This contribution details the selective synthesis of different yttrium manganese oxides through assisted metathesis reactions between MnO, YCl, and ACO under flowing oxygen; where A = Li, Na, K. With lithium carbonate, the orthorhombic perovskite o-YMnO (o-YMnO) forms over the temperature range of 550-850 °C. With sodium carbonate, the pyrochlore YMnO forms at 650 °C. No apparent selectivity is observed with KCO, and all alkalis yields hexagonal YMnO at T > 950 °C. The alkali species modify the reaction pathway and thus impart kinetic control in the formation of both phases.
复杂氧化物的合成需要高温来克服固态扩散带来的障碍；因此，反应通常会生成给定组成下最稳定的多晶型物。为了合成新的或亚稳复杂氧化物，必须设计具有较低初始能量势垒的动力学上可行的反应来控制反应途径和产物。本贡献详细描述了通过在流动氧气下 MnO、YCl 和 ACO 之间的辅助复分解反应选择性合成不同的钇锰氧化物；其中 A = Li、Na、K。在碳酸锂存在下，温度范围为 550-850°C 时形成正交钙钛矿 o-YMnO (o-YMnO)。在碳酸钠存在下，焦绿石 YMnO 在 650°C 形成。用碳酸钾时则没有明显的选择性，所有碱金属在 T > 950°C 时都生成六方 YMnO。碱金属物种改变了反应途径，从而在两种相的形成中赋予了动力学控制。
