Loss evolution of hexagonal Ba0.6Sr0.4La4Ti4O15 microwave dielectric ceramics
In the present work, Ba0.6Sr0.4La4Ti4O15 (BSLT) ceramics with and without the sintering aid (1 wt% ZnO + 0.25 wt% WO3) were synthesized via the solid-state reaction method. Microwave loss evolutions of Ba0.6Sr0.4La4Ti4O15 were investigated emphatically utilizing thermally stimulated depolarization current (TSDC). The sintering behavior, crystal structure and microwave dielectric properties were contrasted mutually. X-ray diffraction confirms that single phase solid solutions are achieved with a hexagonal perovskite structure. And the addition of the sintering aid causes the movement of diffraction peaks to low angles. Due to the incorporation into lattice, the sintering characteristic has not been improved by the sintering aid. With ZnO and WO3, BSLT sintered at 1500 °C demonstrates microwave dielectric properties of εr = 46, Qf = 21,100 GHz and τf = − 4.6 ppm/°C. Especially, the Qf value displays an obvious drop from 48,600 to 21,100 GHz, thus a near zero τf value may be achieved. The extrinsic loss mechanism associated with defects chemistry is explored and TSDC spectra indicate a distinct difference induced by the sintering aid. It can be manifested that the Qf variation originates in the different concentration of oxygen vacancies in host dielectrics.
This work is supported by the Natural Science Foundation of China (Grant Nos. 51562015 and 51762025), Young scientist of Jiangxi Province (Grant No. 20153BCB23004), the Landing Plan of Jiangxi Province (Grant No. KJLD14075), the Education Bureau of Jiangxi Province (Nos. GJJ160874, GJJ170769 and JXYJG-2016-106) and State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (No. KF201709). The author (X.H. Zhang) would like to thank the support of Chinese Scholarship Council and Hundred abroad visiting scholar project of Jiangxi province.