Effect of mechanical stress on defect equilibrium of nonstoichiometric oxides

本研究旨在通过实验量化机械应力对氧化物材料缺陷平衡的影响，选取(La，Sr)CoO_3、(La，Sr)(Co，Fe)O_3、(La，Sr)FeO_3、La_2NiO_4、Nd-LaMnO_3作为模型材料。将YSZ球压入样品表面，并测量放置在YSZ上的电极与样品上的电极之间的电位随时间的变化。对于缺氧的非化学计量比材料，其电势在加载时突然降低，在释放时增加。在负载保持不变的过程中，电势衰减到原值，其时间常数相当于氧空位扩散的时间常数。应力对化学势的影响是通过电动势的变化来量化的。这与基于相应材料的化学膨胀系数的热力学计算是一致的。

This research aimed at experimental quantification of the effect of mechanical stress on the defect equilibrium of oxide materials, (La,Sr)CoO3, (La,Sr)(Co,Fe)O3, (La,Sr)FeO3, La2NiO4, nd LaMnO3 were selected as the model materials. A YSZ ball was indented onto the sample surfaces and the potential between the electrodes placed on YSZ and on the sample were measured as a function of time. With the materials with oxygen deficient nonstoichiometry, the potential showed sudden decrease upon loading, and increased upon its release. During the load was kept constant, the potential decayed to the original value with a time constant equivalent to that of oxygen vacancy diffusion. The effect of the stress on the chemical potential was quantified from the emf shift. It was consistent with the thermodynamic calculation based on the chemical expansion coefficient of the corresponding materials.