Growth, mechanical and domain structure studies of Na0.5Bi0.5TiO3 single crystal grown by flux growth method

Abstract

Single crystal of sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) has been grown by a high-temperature flux growth method. The mechanical properties of polished single crystal plates were investigated. The Vickers microhardness, (Hv) number of the NBT crystals was found to be ∼3. The fracture toughness and brittleness index of the single crystal were calculated from R-curve is 0.15166MNm−3/2 and 276 m−1/2, respectively. Domain structure and birefringence of <001>pc cut NBT single crystal have been analyzed using polarized light microscopy. At room temperature, a stripe-like dark and bright domain pattern have been observed with preferred orientation along <110> direction having birefringence value of 2 × 10−3. With increasing temperature, birefringence was found to decrease with the disappearance of stripe-like pattern near 225 °C. However, with further increase in temperature, the stripe-like pattern re-appears above 240 °C with polarization reversal. On cooling similar behavior was observed near 205 °C. These results are in concurrence with the dielectric/piezoelectric measurements, and unusual behavior of domains was attributed to the ferroelectric→ferroelastic transition in NBT.