Laboratoire des Oxydes et Fluorures, UMR CNRS 6010, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans cedex 9, France.
Dalton Trans. 2010 Jan 7(1):93-102. doi: 10.1039/b915080c. Epub 2009 Nov 10.
The high temperature demixing/recombination phenomenon previously observed in Ca-substituted La(2)Mo(2)O(9) oxide ion conductors [A. Selmi et al., Solid State Ionics, 2006, 177, 3051; Eur. J. Inorg. Chem., 2008, 1813] has been visualised using scanning electron microscopy and EDX analysis. The demixed state appears as CaMoO(4) straight solid streams erupted from pores within LAMOX grains. The thermal stability study is extended to other alkali and alkaline-earth substituted LAMOX compounds, all of which are shown, in temperature-controlled X-ray diffractograms, to present similar demixing/recombination processes. The most spectacular effect is observed in La(1.88)K(0.12)Mo(0.6)W(1.4)O(8.88) where demixing takes the form of a total decomposition, before full recombination at a higher temperature. Such a phenomenon is interpreted as originating from temperature-dependent solid solution limits with higher substitutional ranges at higher temperatures. It results in the metastabilisation of pure phases by quenching (or rapid cooling), whereas the stable state is demixed, as shown on slowly cooled samples.
先前在 Ca 取代 La(2)Mo(2)O(9) 氧化物离子导体中观察到的高温分凝/重组现象[A. Selmi 等人，《固态离子学》，2006 年，177，3051；《欧洲无机化学杂志》，2008，1813]已通过扫描电子显微镜和 EDX 分析得到可视化。分凝状态表现为从 LAMOX 晶粒内的孔隙中喷发出来的 CaMoO(4)直固体流。热稳定性研究扩展到其他碱金属和碱土金属取代的 LAMOX 化合物，所有这些化合物在温度控制的 X 射线衍射图中均显示出类似的分凝/重组过程。在 La(1.88)K(0.12)Mo(0.6)W(1.4)O(8.88)中观察到最显著的效果，其中分凝表现为完全分解，然后在更高温度下完全重组。这种现象被解释为源于温度相关的固溶体极限，在更高温度下具有更高的取代范围。它通过淬火（或快速冷却）使纯相亚稳化，而稳定态是分凝的，正如在缓慢冷却的样品上所显示的那样。
