Abstract: The (Ba_1-xSr_x)La₄Ti₄O₁₅ (x=0.8-0.95) ceramics were prepared by the solid-state reaction method and the phase compositions, crystal structures and microwave dielectric properties were investigated. The results show that the (Ba_1-xSr_x)La₄Ti₄O₁₅ ceramics have the main phase of SrLa₄Ti₄O₁₅ and the second phase of SrLa₈Ti₉O₁₅. The SEM images indicate that the Ba_0.2Sr_0.8La₄Ti₄O₁₅ ceramic with dense microstructures has grain sizes of about 10-20 μm and clear crystal boundaries. The grain shapes of the (Ba_1-xSr_x)La₄Ti₄O₁₅ ceramics change with increasing x values, and the pores in the samples increase. (Ba_1-xSr_x)La₄Ti₄O₁₅ ceramics with x=0.8 possesses excellent microwave dielectric properties, listed as follows, the dielectric constant ε_r =40.86, the quality factor Q×f≈62806 GHz, and the temperature coefficient of resonant frequency τ_f =-20×10^-6/℃. The monotone increases of the dielectric constant εr and the quality factor Q×f of the ceramics with increasing Ba²⁺ contents, mean that the proper substitution of Ba²⁺ for Sr²⁺ can improve microwave dielectric properties of the (Ba_1-xSr_x)La₄Ti₄O₁₅ ceramics.

Key words: microwave dielectric ceramic, perovskite-like structure, microwave dielectric property;SrLa₄Ti₄O₁₅