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

该提案是“极性氧化物中的周期性低维缺陷结构”研究小组的一部分，该小组致力于使用铌酸锂-钽酸锂（LiNb_(1-x)Ta_xO_3， LNT）模型系统研究缺陷结构，电子和离子输运和机电性能的相关性。本文主要研究熔体中LNT固溶体单晶的生长。为此，将首次采用热分析的方法对LiNbO3-LiTaO3体系的相图进行定量评价。从端元LiNbO3和LiTaO3的一致熔融组成开始，通过Czochralski技术可以生长出不同Nb/ ta比的晶体，均匀地覆盖整个固溶体范围。将施加电场来实现生长晶体中铁电畴的原位取向。根据电场类型（交流/直流），可以得到单畴晶体或具有周期畴图案的晶体。在数值模型实验的支持下，将研究熔体和生长晶体中热量和物质的传递。这项工作将着重于组分和掺杂剂的分离及其对生长前沿稳定性的影响。将详细阐述与本课组主要目标相关的生长条件对掺杂物质分布系数的影响，并建立描述相关物质宏观和微观分布的定量分离模型。熔体和固溶体晶体在生长过程中对输运现象有重要影响的基本性质将在熔点附近的感兴趣的温度范围内首次测量或重新测量。在此基础上，将推导出结构完善、化学均匀性好的固溶体晶体生长的最佳条件。从生长的晶体中，将准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.