Low-temperature sintering of Ba 6−3 xSm 8+2 xTi 18O 54 microwave dielectric ceramics by B 2O 3 and GeO 2 addition

Abstract

Tungsten-bronze-type like Ba 6−3 x Sm 8+2 x Ti 18O 54 solid solutions (BST) have been known to show relatively high dielectric constants ( ε r=80), excellent quality factor ( Q· f=10,700 GHz) and good temperature coefficient of resonant frequency ( τ f =−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 B 2O 3 and GeO 2 additives. In the all additive systems investigated, the single addition of B 2O 3 ceramic powders was most effective for lowering the sintering temperature of BST ( x=2/3). When 0.5 wt.% of B 2O 3 ceramic powder was mixed with starting BST mixtures and sintered at 1473 K, the derived ceramics demonstrated dense microstructure with a large permittivity ( ε r=76), high quality factor ( Q· f=10,500GHz) and low temperature coefficient of resonant frequency ( τ f =−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).