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

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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.