Abstract
BaTiO3-based fine powders, with Ba/Ti ratios ranging from 0.98 to 1.05, or comprising CuO up to 1mol%, were synthesized by the spray pyrolysis technique. Starting solutions were prepared by dissolving Ba(NO3)2, Ti[(CH3)2CHO]4, and Cu(NO3)2⋅3H2O in diluted nitric acid, and they were sprayed into the reaction chamber at 800°C through a 2-fluid atomizer with pressurized oxygen gas. The obtained powder particles were hollow spheres 2μm across on the average, which consisted of very small primary particles of around 10nm. The powders were mostly BaTiO3 with small amounts of residual compounds, which however, were removed completely by calcining at 620°C for 1h in an oxygen atmosphere. The calcination at 620°C did not change the particle size. The Ba/Ti ratio of the powders affected the density and the microstructure of sintered bodies. An excess of BaO enhanced densification and gave a grain size discernibly larger than that of stoichiometric composition, whereas a sample containing excess TiO2 component showed marked grain growth which caused the lower bulk density. When the Ba/Ti ratio was 1.03, the relative densitiy of 95% was achieved at the lowest sintering temperature of 1250°C without sintering aids. It should be noted that addition of CuO to the powders with Ba/Ti ratio of 1.03 contributed to reducing the sintering temperature. Addition of 0.5mol% CuO decreased the sintering temperature to 1060°C. The obtained sintered body showed a dielectric constant of 2300, dielectric loss of 0.9% at room temperature, and Curie temperature of around 130°C.
