Effect of ferroelectric phase evolution on dielectric and piezoelectric properties in yttrium-doped BNT-BT ceramics

Lead-free Yttrium-substituted 0.94(Bi0.5-xYxNa0.5TiO3)-0.06(BaTiO3) (BYNT-6BT) ceramics with x = 0, 0.01, 0.02, 0.03 and 0.05 were prepared by conventional solid-state reaction route. The effects of Y3+ substitution into A-site on the crystal structure, microstructure, dielectric, ferroelectric and field induced strain (S-E) behavior of BNT-6BT were examined. X-ray diffraction data revealed that Y2O3 in the amount of 0.1–0.5 wt% can substitute the lattice of BNT-6BT ceramics forming a pure perovskite phase without any secondary peaks. Y3+ introduction enhanced the ferroelectric properties (remnant polarization (Pr) = 36.5 μC/cm2, coercive field (Ec) = 32.96 kV/cm) at x = 0.01 and piezoelectric properties (converse/dynamic piezoelectric constant (d*33) = 327 pm/V at applied electric field of 5 kV/mm) at x = 0.02, which can be attributed to phase evolution and high relative density. Y3+ substitution reduced the relative permittivity, while temperature stability of BNT-6BT was expanded as the Y3+ content increased, which is credited to phase evolution from normal ferroelectric to relaxor ferroelectrics. Outstanding stability range of dielectric permittivity (εr) ±15% from 97 to 500 °C having low dielectric loss (tan δ < 0.01) was achieved at an optimum composition (x = 0.05). The thermally stable dielectric properties of the current study imply that BYNT-BT could be a potential choice for high temperature dielectric applications.