Kinetic unmixing and kinetic decomposition of oxides in external electric fields

三元氧化物AmBnOx（或甚至具有多于四个阳离子的多元氧化物）正被用于暴露于各种热力学力（例如氧化学势梯度）的许多装置中。（固体氧化物燃料电池），电势梯度（或电场）（电解槽、多层陶瓷电容器）、热梯度（热电），应力梯度（压电）等。材料范围从纯离子导体（例如用于固体氧化物燃料电池的电解质，电解槽或锂离子电池）到混合导体和半导体（例如固体氧化物燃料电池和电解槽中的互连和电极）。当这些三元氧化物暴露于外部驱动力（或处于操作下）时，特别是在高温下，其中组成氧化物的离子更移动的，阳离子通常以不同的迁移率迁移。因此，阳离子的浓度梯度在相反的方向上建立，即较快的阳离子将在传输方向上富集，反之亦然。这种现象被称为动力学分解，如果分解的程度足够大，原始氧化物将经历动力学分解，即新相将形成。除了这些解混和分解现象之外，表面的形态变化也可能出现。 正如在SPP 1959年的第一阶段，这是第二阶段的建议，系统地研究在外部电场中的三元或更高的氧化物的动力学不混合和动力学分解的总目标。在SPP 1959年的第一个时期，成功地解决了关于氧化物在电场中使用可逆电极时动力学分解电压的形式推导的主要理论问题。在第二阶段，我们将总结前面的分析，并继续进行相关的实验研究。此外，我们将使用所谓的Hebb-Wagner极化技术研究离子阻挡电极的分解。 总之，将三元或更高的氧化物暴露于所施加的电压可能导致各种动力学解混和分解现象，这取决于所使用的电极的性质（两者都是可逆的;一种是可逆的，一种是离子阻断的）。这些现象需要从理论和实验两个方面进行深入的研究。

Ternary oxides AmBnOx (or even multinary oxides with more than four cations) are being used in numerous devices that are exposed to various thermodynamic forces, such as oxygen chemical potential gradient (solid oxide fuel cells), electric potential gradient (or electric field) (electrolyzers, multi-layered ceramic capacitors), thermal gradient (thermoelectrics), stress gradient (piezoelectrics), etc. The materials range from purely ionic conductors (e.g. electro-lytes for solid oxide fuel cells, electrolyzers or lithium-ion batteries) to mixed conductors and semiconductors (e.g. interconnects and electrodes in solid oxide fuel cells and electrolyzers). When these ternary oxides are exposed to external driving forces (or put under operation) especially at high temperatures where the ions that compose the oxide are more mobile, the cations migrate, in general with different mobilities. As a consequence, concentration gradients of the cations are built up in opposite directions, i.e. the faster cation will be enriched in the direction of transport and vice versa. This phenomenon is called kinetic unmixing, and if the extent of unmixing becomes large enough, the original oxide will undergo kinetic decomposi-tion, i.e. new phases will form. In addition to these unmixing and decomposition phenomena morphological changes of the surfaces may appear. As in the first period of SPP 1959, it is the general aim of this proposal for the second period to investigate systematically the kinetic unmixing and kinetic decomposition of ternary or higher oxides in an external electric field. The main theoretical problem concerning the formal deriva-tion of the kinetic decomposition voltage of an oxide, that is exposed to an electric field using reversible electrodes was successfully solved within the first period of SPP 1959. In the sec-ond period we will generalize the previous analysis and continue the related experimental in-vestigations. In addition, we will investigate decomposition with ion-blocking electrodes using the so called Hebb-Wagner polarization technique. In summary, the exposure of a ternary or higher oxide to an applied voltage may result in a variety of kinetic unmixing and decomposition phenomena, depending on the nature of the used electrodes (both reversible; one reversible and one ion-blocking). These phenomena need fur-ther detailed investigations on a theoretical and on an experimental level as well.