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)Ba0.6Sr0.4La4Ti4O15-xTiO(2) (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, TiO2- 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)Ba0.6Sr0.4La4Ti4O15-xTiO(2) 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 39300-53400GHz. However, the temperature coefficient of resonant frequency ((f)) changes from -7.5 to-9.4ppm/degrees C, and then turns to +3.9ppm/degrees C. A near zero (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.