Loss evolution of hexagonal Ba_0.6Sr_0.4La₄Ti₄O₁₅ microwave dielectric ceramics

In the present work, Ba_0.6Sr_0.4La₄Ti₄O₁₅ (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 Ba_0.6Sr_0.4La₄Ti₄O₁₅ 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 ε_r = 46, Qf = 21,100 GHz and τ_f = − 4.6 ppm/°C. Especially, the Qf value displays an obvious drop from 48,600 to 21,100 GHz, thus a near zero τ_f 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.