Crystal structure, ferroelectric and piezoelectric properties of epitaxial (1-x)(Bi_0.5Na_0.5)TiO₃-x(Bi_0.5K_0.5)TiO₃films grown by hydrothermal method

The composition dependencies of crystal structure, and electrical and electromechanical properties were systematically investigated for epitaxial films of (1-x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3 [(1-x)BNT-xBKT (x = 0 -1)] deposited on (100) c SrRuO3//(100)SrTiO3 substrates by a hydrothermal method. An In-plane crystal lattice was clamped by that of underlying SrRuO3 irrespective of the x value. The dielectric constant decreased monotonously with increasing x. The polarization-electric field hysteresis loops were imprinted due to the preferential polarization in the films. In addition, the increase of tetragonality with increasing x value contributes to the increase of saturation and remnant polarization (P sat. and P r, respectively), coercive field (E c) as well as P r/P sat. values. The effective piezoelectric coefficient (near E = 0 kV cm-1) improved considerably with increasing x, reaching a maximum of 62 pm V-1 in the BKT film. A comprehensive and systematic study has been performed on (1-x)BNT-xBKT epitaxial films in this work, which lays the foundation for further research of this system in the future.