Dependence of microwave dielectric properties on ceramics filler in wollastonite glass-ceramics

Abstract

The effect of various ceramics fillers (TiO2, CaTiO3, SrTiO3, Sr0.8Ca0.2TiO3) on the microwave dielectric properties of wollastonite glass-ceramics was investigated as a function of the content and particle size of the ceramics filler. The temperature coefficient of resonant frequency (TCF) of the specimen increased as the amount of ceramics filler was increased. In addition, the TCF value of the specimens could be tailored to be nearly zero when 10 wt.% ceramics fillers were added except in the case of TiO2. As the amount of ceramics filler was increased, the quality factor (Qf) of the specimens decreased because of the formation of mixture phases of wollastonite and ceramics filler, while the dielectric constant (K) of the specimens increased owing to the fact that the ceramics fillers have higher K values than wollastonite glass-ceramics. When the particle size of the ceramics fillers was increased, the Qf and K value decreased because the specimens with a small particle size of ceramics filler showed larger crystallite size than the others; however, the TCF value did not change significantly with the particle size of the ceramics filler. The optimum dielectric properties of K = 8.66, Qf = 33,800 GHz and TCF = -2.1 ppm/°C were obtained for the specimens with 10 wt.% CaTiO3, heat-treated at 725°C for 7 h and crystallised at 900°C for 3 h.