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

Sol–gel derived Ba_0.80Sr_0.20TiO₃ (BST) and Pb_0.82La_0.18TiO₃ (PLT) powders and a low-melting PbO–B₂O₃ glass powder were mixed to prepare paste. The composite thick films (～40 μm) 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 °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 Ba_0.80Sr_0.20TiO₃ and Pb_0.82La_0.18TiO₃ perovskite phases have been fabricated by using the PbO–B₂O₃ glass as a sintering aid. Compared to conventional sintering at ≥1200 °C, high densification of the composite thick films is achieved at temperature as low as 800 °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 °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 °C.