Effects of Gd substitution on microstructures and low temperature dielectric relaxation behaviors of SrTiO3 ceramics

In this paper, Sr1 - 3x/2GdxTiO3 ceramics (0.00 ≤ x ≤ 0.05) were prepared from powders obtained by a sol–gel method. X-ray diffraction results showed that the Gd ion substituted Sr site, and the unit cell volume of doped samples decreased with increasing Gd doping concentrations, which was due to the difference between Sr/Gd ionic radii. Moreover, the structural change also led to an increase in the antiferrodistortive transition temperature. Dielectric properties of all samples were investigated over broad temperature and frequency ranges, and four dielectric relaxation behaviors were identified in different samples. It was found that two intrinsic dielectric relaxation behaviors for the pure SrTiO3 ceramics could be gradually disappeared with increasing Gd doping concentrations, which was ascribed to the change of domain state induced by Sr vacancies. On the other hand, the other two dielectric relaxation behaviors were induced by Gd doping. The relaxation behavior with activation energy in the range of 100–130 meV was originated from oxygen vacancies, while another relaxation behavior with activation energy in the range of 200–230 meV corresponded to the thermal motions of Ti⁴⁺ ions.