Microstructure and microwave sielectric properties of (Sr_1-xBa_x)La₄Ti₄O₁₅ ceramics

(Sr_1-xBa_x)La₄Ti₄O₁₅(x=0~1, BSLT) microwave dielectric ceramics were fabricated by the conventional solid state reaction method. The phase composition, microstructure and microwave dielectric properties of BSLT ceramics were investigated. The results show that adding Ba²⁺ into BSLT ceramics would help to lower sintering temperature. The La₂TiO₅ main phase was observed in the ceramics besides the second phase of (Sr, Ba)La₄Ti₄O₁₅. With increasing the content of Ba²⁺, the dielectric constant and the value of Q×f increases firstly and then decreases and the value of the temperature coefficient of resonance frequency ranges from -4×10^-6/℃ to -11×10^-6/℃. The ceramic with composition of (Sr_0.9Ba_0.1)La₄Ti₄O₁₅ shows the optimal dielectric properties: ε_r=47.5, Q×f=31 582 GHz, τ_f =-7.5×10^-6/℃.