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 )Bi 0.5+ x (Na 0.78 K 0.22 ) 0.5−3 x TiO 3 – y LaAlO 3 ( 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 )Bi 0.5+ x (Na 0.78 K 0.22 ) 0.5−3 x TiO 3 – y LaAlO 3 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 Bi 3+ 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 6 kV/mm was observed in 0.99Bi 0.505 (Na 0.78 K 0.22 ) 0.4985 TiO 3 –0.01LaAlO 3 ( x =0.005, y =0.01) ceramics sintered at 1150 °C for 2 h.