Phase transitions and physical properties in Ca-modified Na_1/2Bi_1/2TiO₃-SrTiO₃-PbTiO₃ solid solutions

Abstract

The influence on the relaxor state and phase transitions are studied when Sr in 0.4Na1/2Bi1/2 TiO3-0.4SrTiO3-0.2PbTiO3 is gradually replaced by Ca. The concentration dependence of the tetragonal cell volume confirms replacement of Sr by Ca in the lattice, while tetragonality remains independent of Ca concentration in a certain concentration range. The stability of the relaxor state and temperature of phase transition is also weakly dependent on Ca at low concentrations of Ca, and steeply increases starting from a certain Ca concentration. The stability of the phase transition and polarization at low concentrations of Ca and simultaneous steep decreasing of dielectric permittivity values with increasing Ca content is explained assuming that in this concentration range Ca resides inside polar nanoregions, preventing their reorientation in weak external electric field.