Defects and Orientation Dependent Transport in Orthosilicates

本文对A = Co, Ni， Mn的A2SiO4型非立方正硅酸盐中以橄榄石结构结晶的缺陷结构及其扩散进行了光谱学研究。在高温和确定的氧活性下进行的光谱实验将提供有关电子缺陷（空穴）和材料中氧化还原过程的化学扩散的信息。由于橄榄石的正交结构，氧化和还原动力学表现出明显的依赖于晶体取向。通过将化学扩散数据与美国同行获得的示踪剂扩散数据进行比较，开辟了一种新的可能性，可以从输运数据中确定阳离子空位的浓度，然后将其与热重法的直接数据进行比较，以阐明阳离子扩散的复杂行为的细节。对于不同取向的晶体，将测量过渡金属正硅酸盐的电导率作为温度和氧活度的函数。在小极化子模型的框架下，电导率与缺陷对光谱的贡献密切相关。通过对这些数据的比较，可以得到关于小极化子跳变的微观机理和几何结构的详细信息。

An optical spectroscopy study is proposed into the defect structure and the diffusion of defects in non-cubic orthosilicates of the type A2SiO4 with A = Co, Ni, Mn, which crystallize in the olivine structure. The spectroscopic experiments performed at high temperatures and defined oxygen activities will provide information on electronic defects (holes) and on the chemical diffusion responsible for redox processes in the material. Due to the orthorhombic structure of olivines, the kinetics for oxidation and reduction exhibits a pronounced dependence on crystal orientation. By comparison of chemical diffusion data with tracer diffusion data obtained by the American counterpart, a novel possibility is opened to determine the concentration of cation vacancies from transport data, which can then be compared with the direct data from thermogravimetry to elucidate details of the complex behavior of cation diffusion. The electrical conductivity of the transition metal orthosilicates will be measured as a function of temperature and oxygen activity for the different orientations of the crystals. In the framework of the small-polaron model, electrical conductivity is intimately related to the defect-induced contribution to optical spectra. From a comparison of these data detailed information is available on the microscopic mechanism and geometry of small-polaron hopping.