Low-temperature sintering of Ba6−3xSm8+2xTi18O54 microwave dielectric ceramics by B2O3 and GeO2 addition

Tungsten-bronze-type like Ba6−3xSm8+2xTi18O54 solid solutions (BST) have been known to show relatively high dielectric constants (εr=80), excellent quality factor (Q·f=10,700 GHz) and good temperature coefficient of resonant frequency (τf=−15 ppm/K) at x=2/3. However, lower sintering temperature has been asked for the commercial request, since the sintering temperature is higher than 1733 K. In this study, we tried to lower the sintering temperature by several kinds of B2O3 and GeO2 additives. In the all additive systems investigated, the single addition of B2O3 ceramic powders was most effective for lowering the sintering temperature of BST (x=2/3). When 0.5 wt.% of B2O3 ceramic powder was mixed with starting BST mixtures and sintered at 1473 K, the derived ceramics demonstrated dense microstructure with a large permittivity (εr=76), high quality factor (Q·f=10,500GHz) and low temperature coefficient of resonant frequency (τf=−19 ppm/K). It is noteworthy that the sintering temperature was significantly lowered by 260 K compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST (x=2/3).