Orientation‐Dependence of Thermal Depolarization and Phase Development in Bi1/2Na1/2TiO3‐BaTiO3 Single Crystals

The direction-dependence of pyroelectric properties of (1 − x)Bi1/2Na1/2TiO3 − xBaTiO3 (BNT − 100xBT) is investigated, using single crystal samples with well-defined orientations for x = 0.036 and x = 0.063. The results are compared with those of temperature-dependent measurements of the ferroelectric and dielectric hysteresis. The depolarization temperature Td of each crystal composition is found to depend on crystal orientation, a fact that is explained by differences in the stability of respective domain configurations. A rationalization is offered for the observation that Td differs from the ferroelectric-relaxor transition temperature, depending on orientation. The hysteresis curves of BNT − 3.6BT are typical for a rhombohedral system with a ferroelectric-relaxor transition, with polarization reversal close to Td occurring in a multistep process that includes decay of ferroelectric domains into polar nanoregions and re-formation of domains. BNT − 6.3BT, a composition in the region of the morphotropic phase boundary, shows the same feature, but additionally is characterized by a field-induced transition between rhombohedral and tetragonal symmetry. This combination results in an effective piezoelectric coefficient of d33*=1886 pm/V.