Novel thermally stable, high quality factor Ba4(Pr0.4Sm0.6)28/3Ti18-yGa4y/3O54 microwave dielectric ceramics

High dielectric constant Ba-4(Pr0.4Sm0.6)(28/3)Ti18-yGa4y/3O54 (BPSTG) (0 <= y <= 1) microwave ceramics with enhanced dielectric properties were synthesized via the traditional solid-state processing for the first time. The crystal structure, microstructure, and microwave dielectric characteristics were investigated in details. X-ray diffraction results showed that all well-sintered samples belonged to a single tungsten bronze type phase. Results showed that partial substitution of Ga3+ for Ti4+ is an effective way in adjusting the temperature coefficient of resonant frequency (TCF) value of the Ba-4(Pr0.4Sm0.6)(28/3)Ti18O54 ceramics and increased the quality factor (Qf) values. The variation tendency of dielectric constant was in accordance with the ionic polarizability. The Qf values highly depend on the grain size from the scanning electron microscopy results. A near zero TCF value can be obtained by carefully adjusting the substitution of Ga3+ content. Infrared reflectivity (FIR) spectra were employed to reveal the relationship between the phonons and microwave dielectric properties. At last, excellent combinations dielectric properties of epsilon(r) = 78.5, Qf = 12,400 GHz, TCF = +2.1 ppm/degrees C were achieved in BPSTG ceramics when y = 0.75.