Abstract
High quality lead-free Na0.5Bi0.5TiO3 (NBT) single crystals were grown by the Czochralski method. The XRD patterns indicate the perovskite-type structure of rhombohedral symmetry with small amount of tetragonal phase even at room temperature. Structural, Raman scattering, thermal, dielectric and second harmonic generation (SHG) studies were performed for both unpoled and poled samples. The observed features indicate that the electric field applying significantly affects the polar state and causes the increase of a local degree of order and transformation of the tetragonal regions into the rhombohedral phase, and in consequence stabilizes and widens the temperature range of the ferroelectric state. The hysteresis loop, pyroelectric and SHG measurements indicated that in controversial temperature interval (∼200–350 °C) NBT exhibits ferroelectric nature rather than antiferroelectric one, and polar state presence up to approximately 400 °C. Anomalies of the temperature dependences of heat flow (DSC) and thermal expansion (Δl/l0) observed at approximately 165, 330 and 540 °C are connected with so called “depolarization temperature” Td and the phase transitions between the rhombohedral, tetragonal and cubic majority phases, respectively.
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