Crystal Growth and Basic Properties of Lithium Niobate - Lithium Tantalate Solid Solution Crystals

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，该研究组致力于利用LiNb_1-xTa_xO_3（LNT）模型系统研究缺陷结构、电子和离子输运以及机电性能之间的关系，该项目的重点是研究从熔体中生长LNT固溶体单晶。为此，LiNbO 3-LiTaO 3系统的相图将首次通过热分析进行定量评估。从端元LiNbO 3和LiTaO 3的全等熔融组合物开始，将通过直拉技术生长均匀覆盖整个固溶体范围的各种Nb/Ta比的晶体。将施加电场以实现生长晶体中的铁电畴的原位取向。取决于电场的类型（ac/dc），将获得单畴晶体或具有周期性畴图案的晶体。在数值模拟实验的支持下，将研究熔体和生长晶体中的热传递和物质传递。这项工作将有一个强烈的强调成分和掺杂剂的偏析及其对生长前沿的稳定性的影响。将阐述生长条件对与本研究组的主要目标相关的掺杂物质的分布系数的影响，和定量分离模型描述宏观和微观，将首次测量熔体和固溶体晶体的基本性质，这些性质对生长过程中的输运现象有重大影响，在熔点附近的有趣温度范围内重新测量。根据这些结果，将得出最佳条件，使上级结构完美性和化学均匀性的固溶体晶体能够生长。从生长的晶体中，将制备所需规格的样品并交付给项目合作伙伴。

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 (LiNb_(1-x)Ta_xO_3, LNT).This proposal is focussed on investigations of the growth of LNT solid solution single crystals from the melt. For this purpose, the phase diagram of the LiNbO3–LiTaO3 system will be assessed quantitatively by means of thermal analysis for the first time. Starting from the congruently melting compositions of the end members LiNbO3 and LiTaO3, crystals of various Nb/Ta-ratios, evenly covering the whole solid solution range will be grown by the Czochralski technique. An electric field will be applied to achieve in situ orientation of the ferroelectric domains in the growing crystals. Depending on the type of electric field (ac/dc) single domain crystals or crystals with periodic domain patterns will be obtained. Supported by numerical model experiments, transfer of heat and matter in both, melt and growing crystal, will be investigated. This work will have a strong emphasis on the segregation of the constituents and dopants and its impact on the stability of the growth front. The influence of growth conditions on the distribution coefficients of doping species that are relevant for the primary goals of this research group will be elaborated, and quantitative segregation models describing macro- and micro-distribution of the involved species will be developed.Essential properties of melt and solid solution crystals that have a significant impact on transport phenomena during the growth process will be measured for the first time or remeasured in the interesting temperature range near the melting point. Based on these results optimized conditions enabling growth of solid solution crystals of superior structural perfection and chemical homogeneity will be derived.From the grown crystals, samples of desired specifications will be prepared and delivered to the project partners.