The effect of processing conditions on the phase, microstructure and dielectric properties of SrCa4Nb4TiO17 and Ca5Nb4TiO17 microwave ceramics

The effect of processing conditions on the phase, microstructure and dielectric properties of SrCa4Nb4TiO17 and Ca5Nb4TiO17 microwave ceramics was investigated. The ceramics processed via solid state mixed-oxide route were characterized using XRD, Raman spectroscopy and SEM for phase, molecular vibrational modes and microstructural analysis respectively. Dielectric properties at low and microwave frequencies were measured using LCR meter and a vector network analyzer. The XRD results revealed the formation of a single phase for each ceramics. The microstructure was comprised of elongated and plate-like grains. The optimum microwave dielectric properties i.e. temperature coefficient of resonant frequency (τf) ∼ −78 ppm/K, electric permittivity (ɛr) ∼47.2 and quality factor multiplied by the resonant frequency (Q u f o) ∼11954 GHz, were achieved for SrCa4Nb4TiO17, sintered at 1475 °C for 4 h. For Ca5Nb4TiO17, sintered at 1450 °C for 4 h, the respective properties were: τf ∼ −137 ppm/K, ɛr ∼ 42 and Q u f o ∼ 14800 GHz respectively.