Polar nanoregions and dielectric properties in high-strain lead-free 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO3 piezoelectric single crystals

A structural coexistence of rhombohedral (R) and tetragonal (T) phases has been revealed in the (001)(c)-cut lead-free 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO(3) (BNB7T) piezoelectric crystals, which grown by the self-flux method, in the lower temperatures by high-resolution synchrotron X-ray diffraction, reciprocal space mapping, and transmission electron microscopy. The dielectric permittivity exhibits a thermal hysteresis in the region of 120-260 degrees C, implying a first-order-like phase transition from R+T to T. The real part (epsilon') of dielectric permittivity begins to deviates from the Curie-Weiss equation, epsilon' = C/(T - T-o), from the Burns temperature T-B = 460 degrees C, below which the polar nanoregions (or nanoclusters) develop and attenuate dielectric responses. The polar nanoregions of 5-10 nm were revealed by high-resolution transmission electron microscope. The normal piezoelectric coefficient d(33) exhibits a rapid increase at E = 15-20 kV/cm and reaches a maximum of d(33) similar to 450 pC/N. The high piezoelectric response and E-field induced strain in BNB7T single crystals can be attributed to structural phase transitions under an E-field application. (C) 2014 AIP Publishing LLC.