Effects of CaTiO3, BaTiO3, and BaZrO3 on the crystal structures and electrical properties of Bi1/2Na1/2TiO3–SrTiO3 piezoelectric ceramics

This study investigated the effects of CaTiO₃, BaTiO₃, and BaZrO₃ doping on the phase transition and strain properties of lead-free 0.76Bi_1/2Na_1/2TiO₃-0.24SrTiO₃ (BNT-24ST) piezoceramics. The nonergodicity of the BNT-24ST ceramic was stabilized as a function of CaTiO₃ doping, corresponding to the existence of the ferroelectric-to-relaxor phase transition temperature (T_F-R) peak in the dielectric permittivity curves of the samples. However, the BaTiO₃- or BaZrO₃- doped NBT-24ST samples promote the transition from a nonergodic to an ergodic relaxor phase. The 0.01 mol BaTiO₃ or 0.01 mol BaZrO₃ doping decreases the T_F-R peak of the NBT-24ST sample to below room temperature. Interestingly, it is noted that the nonergodic-to-ergodic relaxor phase transition of the BaTiO₃-doped BNT-24ST ceramics was faster than that of the BaZrO₃-doped BNT-24ST ceramics. The 0.01 mol BaTiO₃-doped BNT-24ST sample presents a maximum dielectric constant of ~ 8000. The maximum piezoelectric actuator coefficient (uni-S_max/E_max) of ~ 525 pm/V was observed for the 0.01 mol BaTiO₃-doped BNT-24ST ceramic. The effect of the tolerance factor on the phase transition and electrical properties of the BNT-24ST-ABO₃ ceramics is suggested.