Ion transport and point defects in LiNb_(1-x)Ta_xO_3 solid solutions

这项研究是“极性氧化物中周期性低维缺陷结构”课题组的一部分，该课题组致力于使用模型系统LiNb-LiTa(LNT)研究缺陷结构、电子和离子输运以及机电性能之间的关系。这一子项目的重点是Li、Nb/Ta、O和H物种的离子输运的实验表征和基本了解，以及具有和不具有铁电区的LNT单晶的电导率随温度、氧分压和Nb/Ta含量的变化。必须澄清潜在的点缺陷、缺陷平衡和传输机制。缺陷和输运及其相互作用对材料的宏观性质，如导电性、机电性质、光学性质等有着根本性的影响，它们的知识将允许对性质进行特定的定制。考虑到研究组的总体目标，这一子项目的结果对于理解部分离子电导率及其对总电导率的贡献，对于识别与温度相关的大多数点缺陷和缺陷团簇，以及高温稳定性和化学计量比修饰，具有特别重要的意义。具体地说，还应调查顺电转变和外来原子对扩散的影响。特别令人感兴趣的是迄今未被探索的域壁和相关的缺陷/电荷对离子传输的影响。这项工作也为理解时变原子结构中的极化子动力学奠定了基础。为了确定示踪剂的扩散系数，使用了稳定的示踪同位素，它们要么是从气相(2-H_2O，18-O_2)引入的，要么是通过溅射沉积的(6-Li，180-Ta)。同位素选择性深度剖面分析将使用二次离子质谱仪(SIMS)进行，并使用新的分析方法对选定的系统使用中子反射仪(NR)进行分析。所需的电导率将使用阻抗光谱学来确定。这些结果应该有助于建立一个缺陷模型，该模型解释了离子和电子的传输过程，并为材料性质的定制奠定了基础。

The proposal is part of the research group ´Periodic low-dimensional defect structures in polar oxides´, which is dedicated to the correlation of defect structure, electron and ion transport and electromechanical properties using the model system lithium niobate-lithium tantalate (LNT).Focus of this sub-project is the experimental characterization and basic understanding of the ion transport of the species Li, Nb/Ta, O and H and of the electrical conductivity as a function of temperature, oxygen partial pressure and Nb/Ta content in LNT single crystals with and without ferroelectric domains. The underlying point defects, defect equilibria and transport mechanisms have to be clarified. Defects and transport, as well as their interplay, have fundamental influence on the macroscopic material properties, such as electrical conductivity, electromechanical properties, optical properties etc. and their knowledge will allow a specific tailoring of properties.With regard to the overall goals of the research group, the results of this sub-project are of particular importance for an understanding of partial ionic conductivities and their contribution to total conductivity, for the identification of the temperature-dependent majority point defects and defect clusters as well as for the high temperature stability and stoichiometric modifications. Specifically, the influence of the paraelectric transition and of foreign atoms on diffusion should also be investigated. Of particular interest is the hitherto unexplored influence of the domain walls and the associated defects/charges on ion transport. The work also forms the base for an understanding of polaron dynamics in time-varying atomic structures. To determine the tracer diffusivities, stable tracer isotopes are used, which are either introduced from the gas phase (2-H_2O, 18-O_2) or by means of sputter deposition (6-Li, 180-Ta). The isotope-selective depth profile analysis will be carried out with secondary ion mass spectrometry (SIMS) and for selected systems with neutron reflectometry (NR) using a novel analytical approach. The necessary conductivities will be determined using impedance spectroscopy. The results should contribute to a defect model that explains the ionic and electronic transport processes and forms the basis for a tailoring of materials properties.