The structures and dielectric properties of Ba0.80Sr0.20TiO3/Pb0.82La0.18TiO3 composite thick films with addition of PbO-B2O3 glass

Sol-gel derived Ba0.80Sr0.20TiO3 (BST) and Pb0.82La0.18TiO3 (PLT) powders and a low-melting PbO-B2O3 glass powder were mixed to prepare paste. The composite thick films (similar to 40 mu m) were fabricated by screen-printing the paste onto the Al2O3 substrates with screen-printed silver bottom electrode and then sintered at the low temperature 650-800 degrees C, respectively. X-ray diffraction (XRD), transmission microscope (TEM), scanning electron microscope (SEM) and an impedance analyzer were used to analyze the structures, microstructures and dielectric properties of the powders and the composite thick films. The results show that the composite thick films containing sol-gel derived Ba0.80Sr0.20TiO3 and Pb0.82La0.18TiO3 perovskite phases have been fabricated by using the PbO-B2O3 glass as a sintering aid. Compared to conventional sintering at >= 1200 degrees C, high densification of the composite thick films is achieved at temperature as low as 800 degrees C by the "wetting" and "infiltration" of the liquid phase on the particles. The homogenization of the BST and PLT perovskite phase in the composite thick films is evitable by controlling the sintering temperature and time. The formation of the small amount of pyrochlore phase in composite thick films sintered at 800 degrees C is resulted from both the volatilization of PbO and the interaction between the PLT and PbO-B2O3 glass. The relative dielectric properties of the composite thick films exhibit good temperature-stable behavior, and the variation of the relative dielectric constant is less than 10% in the temperature range 0-300 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.