Effects of A-site vacancies and lanthanum aluminate substitution on the dielectric and electromechanical properties of (1−y)Bi0.5+x(Na0.78K0.22)0.5−3xTiO3–yLaAlO3 lead-free ceramics

Abstract

(1−y)Bi0.5+x(Na0.78K0.22)0.5−3xTiO3–yLaAlO3 (x=0–0.02, y=0–0.01) piezoelectric ceramics were synthesized with a conventional solid state reaction method. The structure and morphology of the (1−y)Bi0.5+x(Na0.78K0.22)0.5−3xTiO3–yLaAlO3 ceramics were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy). The electric polarization, electric-field-induced strain and temperature-dependence dielectric constant were investigated. These results show that a non-polar phase was induced by changing the proportion of content x to have a deficiency of Na+ and K+ and excess of Bi3+ ions. A phase boundary between non-polar and polar (ferroelectric) phases was observed at ambient temperature. The non-polar phase was switched to the polar phase with the application of an electric field. The stability of the induced polar phases strongly depended on the proportion of content x. An enhanced electric-field-induced strain of 0.35% at 6kV/mm was observed in 0.99Bi0.505(Na0.78K0.22)0.4985TiO3–0.01LaAlO3 (x=0.005, y=0.01) ceramics sintered at 1150°C for 2h.