SPRAY-PYROLYTIC SYNTHESIS OF BATIO3-BASED FINE POWDERS AND EFFECT OF BA/TI RATIO AND CUO ADDITION ON THEIR SINTERABILITY

BaTiO3-based fine powders with Ba/Ti ratios ranging from 0.98 to 1.05 or comprising CuO up to 1 mol%, 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 powder particles were hollow spheres 2 μm across on average and consisted of small primary particles of around 10 nm. The powders were mostly BaTiO3 with small amounts of residual compounds which with were removed by calcining at 620°C for 1 h 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 microstructure of sintered bodies. An excess of BaO enhanced densification and gave a grain size larger than that of stoichiometric composition, whereas a sample containing excess TiO2 component showed grain growth which caused lower bulk density. When the Ba/Ti ratio was 1.03, relative density of 95% was achieved at the lowest sintering temperature of 1250°C without sintering aids. Addition of CuO to powders with Ba/Ti ratio of 1.03 contributed to reducing the sintering temperature. Addition of 0.5 mol% CuO decreased the sintering temperature to 1060°C. The sintered body showed a dielectric constant of 2300, dielectric loss of 0.9% at room temperature, and Curie temperature of around 130°C.