Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents Study of (1− <i>x</i> ) <scp> <scp>Ba</scp> </scp> _0.6 <scp> <scp>Sr</scp> </scp> _0.4 <scp> <scp>La</scp> </scp> ₄ <scp> <scp>Ti</scp> </scp> ₄ <scp> <scp>O</scp> </scp> ₁₅ – <i>x</i> <scp> <scp>TiO</scp> </scp> ₂ Ceramics

Abstract

Microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of (1− x ) Ba 0.6 Sr 0.4 La 4 Ti 4 O 15 – x TiO 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, TiO 2−δ as a secondary phase can be detected in the ceramics. The variation of TiO 2 content has a significant effect on the dielectric properties of (1− x ) Ba 0.6 Sr 0.4 La 4 Ti 4 O 15 – x TiO 2 at microwave frequency. The dielectric permittivity of ceramics increases from 44 to 49 with the increase of TiO 2 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 TiO 2 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 TiO 2 content. It can be concluded that the extrinsic dielectric loss is dominated by microstructure and oxygen vacancy defects.