Role of cadmium on the phase transitions and electrical properties of BaTiO₃ ceramics

The search for high piezoelectric and electromechanical properties near morphotropic phase boundaries (MPB) in lead-free ceramics has attracted considerable interest. The MPB can be obtained in the composition-temperature phase diagram by combining stabilized rhombohedral (R) and tetragonal (T) ends, which possess cubic (C) to R or C to T transitions, respectively. The R-end is usually realized by doping ions Zr⁴⁺, Hf⁴⁺ or Sn⁴⁺ at the Ti⁴⁺ site, whereas the T-end can be generated by Ca²⁺ doped at the Ba²⁺ site of BaTiO₃. Our recent computational work (Phys. Rev. B. 93, 144111, 2016) showed that Cd²⁺ doped BaTiO₃ can be considered as a potential T-end. In the present study, we synthesized (Ba_1−xCd_x)TiO₃ ceramics to investigate the effects of Cd²⁺ on the phase transition, dielectric, ferroelectric and piezoelectric properties of the ceramics. Although our results show that Cd²⁺ fails to stabilize the T phase, i.e., the transition temperatures vary little with Cd²⁺ concentration, the electrical properties are found to be optimized for Cd²⁺% of 5%. The optimization of the properties is related to the microstructural features including grain size and sample density.