Suppression of oxygen vacancies generation in Ba6-3xSm8+2xTi18O54 (x=2/3) microwave dielectric ceramics through Pr substitution

Ba6-3x(PrySm1-y)(8+2x)Ti18O54 (x = 2/3, 0 <= y <= 0.25, BPST) solid solutions ceramics were fabricated using the traditional solid-state processing. Interestingly, substitution of Pr for Sm not only increased the relative permittivity (epsilon(r)) and optimized the temperature coefficient of resonant frequency (TCF), but also improved the Q x f value which was unexpected according to the mixing rules. With the increase of y values from 0 to 0.25, the epsilon r gradually increased from 78.1 to 82.9, the Q x f value enhanced from 8300 to 10000 GHz, and the TCF value shifted from -11.5 to +8.8 ppm/degrees C. The improvements of the Q x f value were strongly dependent on the suppression of Ti3+ and oxygen vacancies generation. The TCF value shifted from negative to positive owing to the decreasing of the tilt angle of TiO6 octahedral, which could be confirmed by Raman spectra. Infrared reflectivity spectrum analysis illustrated that infrared-active modes at low frequencies under 300 cm(-1) dominated dielectric polarization in the BPST ceramics. Finally, excellent comprehensive properties (epsilon(r) = 80.5, Q x f = 9700 GHz, and TCF = -0.9 ppm/degrees C) were obtained for Ba6-3x(PrySm1-y)(8+2x)Ti18O54 ceramic sintered at 1375 degrees C.