Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents Study of (1−x)Ba0.6Sr0.4La4Ti4O15–xTiO2 Ceramics

Microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of (1?x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xTiO₂ (x = 0, 0.01, 0.02, 0.05, and 0.1) ceramics were studied. X‐ray diffraction analysis indicates that the specimens show a hexagonal perovskite structure; however, with an increase of x to 0.1, TiO_2?δ as a secondary phase can be detected in the ceramics. The variation of TiO₂ content has a significant effect on the dielectric properties of (1?x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xTiO₂ at microwave frequency. The dielectric permittivity of ceramics increases from 44 to 49 with the increase of TiO₂ content. The Qf value is in the range of 39 300–53 400 GHz. However, the temperature coefficient of resonant frequency (τ_f) changes from ?7.5 to–9.4 ppm/°C, and then turns to +3.9 ppm/°C. A near zero τ_f value can be obtained by tuning the content of TiO₂ addition. TSDC was also employed to analysis the extrinsic loss mechanism. Utilizing a fixed polarization condition, the TSDC relaxation peaks are present, which are generated by oxygen vacancies. And the concentration of oxygen vacancies increases with the increase of TiO₂ content. It can be concluded that the extrinsic dielectric loss is dominated by microstructure and oxygen vacancy defects.