Microstructure and properties of (Ca,Sr,Ba)La₄Ti₄O₁₅ medium-entropy microwave dielectric ceramics

Medium-entropy microwave dielectric ceramics with intermediate permittivity, (Ca,Sr,Ba)La₄Ti₄O₁₅(BSCLT), were synthesized via a conventional solid-state reaction method. The effects of configurational entropy and cationic variation on the microwave dielectric properties were systematically investigated. X-ray diffraction (XRD) confirmed that the main crystalline phase was MeLa₄Ti₄O₁₅, accompanied by a secondary phase of La₂Ti₂O₇. Raman spectroscopy provided further insights into the crystal structure, and X-ray photoelectron spectroscopy (XPS) was employed to analyze the elemental composition and valence states. The well-sintered BSCLT ceramics exhibited relatively stable dielectric constants (ε_r), with Q×f values ranging from 32,484 to 37,515 GHz, and temperature coefficients of resonant frequency (τ_f) varying between −18.4 and 11.2 ppm/℃. Among them, the composition (Ca_0.4Sr_0.4Ba_0.2)La₄Ti₄O₁₅ exhibited optimal microwave dielectric performance: ε_r = 45.6, Q×f = 37,515 GHz, and τ_f = -3.5 ppm/℃.