High Insulation Resistivity and Ultralow Dielectric Loss in La-Doped SrTiO3 Colossal Permittivity Ceramics through Defect Chemistry Optimization

High performance LaxSr1–xTiO3 (0.000 ≤ x ≤ 0.018) ceramics were prepared by a traditional solid-state method and sintered in nitrogen atmosphere. The phase structure and micromorphology of the ceramic samples were studied by the analysis of XRD and SEM, respectively. A small amount of La ion doping promoted the growth of ceramic grains, and no second phase was found. Meanwhile, the La0.010Sr0.990TiO3 ceramic sample showed a colossal permittivity of 26 897 and a dielectric loss of 0.005 at 1 kHz, and a colossal permittivity of 26 072 and a dielectric loss of 0.031 at 1 MHz, with high insulation resistivity (3.10 × 109 Ω·cm, DC 100 V) and good stability of frequency (20 Hz to 2 × 106 Hz) and temperature (25–300 °C). Then the mechanism of obtaining excellent dielectric properties was investigated via treatment with different atmospheres and XPS and impedance analysis. As a result, colossal permittivity and ultralow dielectric loss were attributed to the TiTi′–VO··–TiTi′ defect dipoles and VO··–3TiTi′–LaSr· defect dipole clusters. In addition, the main reason for the high DC resistivity of the ceramic samples was the insulation grain boundaries with high resistance. Consequently, colossal permittivity, low dielectric loss, high insulation resistivity, and good stabilities of frequency and temperature of the ceramic samples were obtained at the same time.