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

该项目是“极性氧化物中周期性低维缺陷结构”研究组的一部分，该研究组致力于使用锂-钽酸锂模型系统（LNT）研究缺陷结构、电子和离子输运以及机电性能的相关性。该子项目的重点是Li，Nb/Ta，O和H以及电导率作为温度、氧分压和Nb/Ta含量的函数。潜在的点缺陷，缺陷平衡和输运机制必须澄清。缺陷和输运，以及它们之间的相互作用，对材料的宏观性能，如电导率，机电性能，光学性能等有着根本性的影响，它们的知识将允许对性能进行特定的调整。关于研究小组的总体目标，该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特别重要，用于识别与温度相关的多数点缺陷和缺陷簇，以及用于高温稳定性和化学计量修改。具体来说，还应研究顺电跃迁和外来原子对扩散的影响。特别令人感兴趣的是迄今尚未探索的影响的域壁和相关的缺陷/电荷的离子传输。这项工作也形成了理解极化子动力学随时间变化的原子结构的基础。为了测定示踪剂的扩散系数，使用了稳定的示踪同位素，它们可以从气相中引入（2-H_2O，18-O_2），也可以通过溅射沉积的方法引入（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法进行，并使用一种新的分析方法对选定的系统使用中子反射法进行。必要的电导率将使用阻抗谱法测定。结果应有助于解释离子和电子传输过程的缺陷模型，并形成剪裁材料性能的基础。

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.