Preparation, characterization and sintering behavior of barium titanate powders coated with Ba-, Ca-, Si- and Ti-containing components

Abstract

An emulsion technique and spray drying were used to prepare BaTiO3 powders coated with additives. Different additive compositions (TiO2; TiO2/SiO2; CaO/TiO2/SiO2; 2BaO/TiO2/2SiO2) were used in the form of their aqueous precursor solutions. The as-received powders were compared with powders of the same composition manufactured by conventional wet-milling. The coating of the BaTiO3 powder positively influences the sintering behavior. Isothermal dilatometric measurements show that the activation energy &Delta;E of the shrinkage of the coated powders is lower than that of the powders prepared by milling. This is caused by the homogeneous distribution of the additive. The activation energy for the different additives changes in the following sequence: &Delta;E(2BaO/TiO2/2SiO2) < &Delta;E(TiO2) < &Delta;E(CaO/TiO2/SiO2) < &Delta;E(TiO2/SiO2). This sequence correlates with the amount of Ba ions necessary to diffuse out of the BaTiO3 matrix to form the secondary phases Ba2TiSi2O8 or Ba6Ti17O40, respectively.