The structural and electric properties of Li- and K-substituted Bi0.5Na0.5TiO3 ferroelectric ceramics

Research highlights: This paper describes the structure, dielectric properties, phase transition and piezoelectric properties of Li/K substituted sodium bismuth titanate based lead-free piezoelectric ceramics systematically. According to the structure and hysteresis loop, the mechanism of the phase transition and the depolarization is explained. Until now, the content of these studies, especially the phase transition at depolarization temperature in lithium and potassium modified Bi0.5Na0.5TiO3 ceramics has not been reported. And for the composition near the morphotropic phase boundary, the optimal piezoelectric properties have been obtained. - Abstract: The structure, dielectric properties and phase transition of lithium and potassium modified Bi0.5Na0.5TiO3 ceramics were investigated widely. The phase transition behavior with respect to changes in composition and temperature was investigated using X-ray diffraction analysis, dielectric and ferroelectric characterizations. The experimental results show that there is a diffusion phase transition in (Na1-xKx)0.5Bi0.5TiO3 ceramics at Tm and the diffuseness of the phase transition is more obvious for the samples near the morphotropic phase boundary. In (Na1-xLix)0.5Bi0.5TiO3 system, due to the space charge polarization induced by ions conductivity, the low frequency permittivity increases so remarkably at high temperature that the peak of maximum permittivity vanishes. The hysteresis loops at different temperatures indicate that there is no existence of anti-ferroelectrics in lithium and potassium modified Bi0.5Na0.5TiO3 ceramics above the depolarization temperature Td. The depolarization reason is that the tetragonal nonpolar phase occurs and leads to the macro-micro domain transformation at about Td.