Structures and dielectric properties of (Nb, Zn) co-doped SrTiO₃ ceramics at various sintering temperatures

Effects of sintering temperatures on the phases, microstructures, defect structures and dielectric behaviors of the SrTi_0.985(Nb_2/3Zn_1/3)_0.015O₃ ceramics have been systematically investigated. Giant permittivity (~ 10100) and low tangent loss (~ 0.035) are achieved in the ceramics sintered at 1500 °C. With an increase in sintering temperature, the grain size increases first and then stabilizes gradually, while the lattice constant increases first and then decreases. Higher sintering temperature is beneficial to the thermal stabilities of permittivity and tangent loss. Further investigations reveal that the giant permittivity mainly results from defect polarization. More Ti³⁺ ions and more oxygen vacancy-related defect complexes (\( {\text{Ti}}^{3 + } - {\text{V}}_{\text{O}}^{ \cdot \cdot } - {\text{Ti}}^{3 + } \) and \( {\text{V}}_{\text{O}}^{ \cdot \cdot } - {\text{Zn}}_{\text{Ti}}^{\prime \prime } \), etc.) are involved in the ceramics sintered at 1500 °C, contributing to the giant permittivity and low tangent loss. The presence of point defects breaks the local structural symmetry and distorts the oxygen octahedron. Dielectric properties are deteriorated at excessive sintering temperature due to the dissociation of defect complexes as well as the enhanced interfacial polarization.