Colossal permittivity and defect-dipoles contribution for Ho0.02Sr0.97TiO3 ceramics

High-performance dielectric materials arouse persistently considerable attention due to their potential in the field of solid state capacitors. Ho-doped SrTiO3 ceramics with the composition of Ho0.02Sr0.97TiO3 were prepared by the solid state reaction technique. Structure, colossal dielectric behavior and relaxation mechanism of Ho0.02Sr0.97TiO3 ceramics were investigated in detail. The results indicated that Ho substitution of 0.02 content into the host materials maintain a single cubic perovskite structure. The Ho0.02Sr0.97TiO3 ceramics sintered at high temperature (1350 °C) show colossal permittivity (up to 4908 at 10 kHz) with low dielectric loss (about 0.03) at room temperature, and good dielectric stability over a broad frequency range of 100 Hz - 100 kHz as well. Four kinds of dielectric relaxations are present in a broad temperature range from −140 to +350 °C. Thermally stimulated depolarization current (TSDC) measurements were performed to explore the defects associated relaxation process. Four polarization relaxation peaks were detected in Ho0.02Sr0.97TiO3 ceramics, and three of them were assigned to defect dipole relaxations. There seems a possibility to form some defect dipoles because of the interactions among the defects available such as Sr vacancies, Ti3+, (HoSr)•, ionized oxygen vacancies and localized electrons. These defect clusters would give rise to relaxation behaviors and thus contribute to the colossal dielectric characteristics.