Origin of the ultrahigh field-induced strain in the Gd-doped 0.854Bi_0.5Na_0.5TiO₃-0.12Bi_0.5K_0.5TiO₃-0.026BaTiO₃ ternary ceramic system

Abstract This study focused on analyzing the ferroelectric, piezoelectric, and dielectric properties of lead-free Bi 0.487 Na 0.427 K 0.06 Ba 0.026 TiO 3 (0.854BNT-0.12BKT-0.026BT) ternary ceramic system by systematically doping 0.001, 0.01, 0.1, 0.5, and 1.0 mol% Gd 2 O 3 . The specific composition that was investigated is located at the tetragonal side of the rhombohedral-tetragonal morphotropic phase boundary (MPB) region. Undoped and Gd-doped BNT-BKT-BT ceramics were produced by the conventional solid-state reaction method. Ferroelectric, piezoelectric, and dielectric properties of ceramics were analyzed by carrying out electrical measurements from sintered samples. An ultrahigh field-induced unipolar strain of 0.52% at 65 kV cm −1 , with a converse piezoelectric coefficient d 33 * of up to 795 pm V −1 , was achieved with 0.5 mol% Gd doping. This was attributed to the Gd dopant disrupting the normal ferroelectric order and leading to the formation of a nonpolar relaxor phase. The field-induced transition from the nonpolar relaxor phase to the normal ferroelectric phase resulted in relatively large field-induced strain values in the 0.5 mol% Gd-doped ceramics. These results suggest that Gd-doped BNT-BKT-BT ceramics hold promise for digital actuator applications.