Growth of (1 − x)(Na_1/2Bi_1/2)TiO₃–xKNbO₃ single crystals by the self-flux method and their characterisation

Single crystals of (Na_1/2Bi_1/2)TiO₃-based compositions are of interest for actuator applications. In this work, single crystals of nominal composition (Na_1/2Bi_1/2)TiO₃ (NBT) and 0.92(Na_1/2Bi_1/2)TiO₃–0.08KNbO₃ (NBT-KN) are grown by the self-flux method and their structure and electrical properties characterized. X-ray diffraction and transmission electron microscopy show that both the NBT and NBT-KN single crystals have a tetragonal structure, whereas polarized light microscopy and Raman scattering indicate a rhombohedral structure. Electron probe microanalysis shows the NBT single crystal is Na-deficient and slightly Bi-excess, while the NBT-KN single crystal is Na-deficient and slightly Bi-excess, slightly Nb-deficient and noticeably K-deficient. Temperature-controlled Raman scattering and measurement of the dielectric properties reveal that the characteristic phase transitions in NBT shift to lower temperatures on formation of a solid solution with KNbO₃. The transitions indicated in the Raman scattering analysis can also be revealed by the impedance modeling parameters in terms of capacitance relaxations by diffusion mechanisms.