Studies on Sintering of Barium Titanate Derived from BaTiO(C₂O₄)₂. 4H₂O: Correlation between Powder Characteristics, Sintering and Dielectric Properties

Abstract

Polycrystalline barium titanate capacitors derived from the mechanical mixture of BaCO₃ and TiO₂ showed changes in the molar ratio between BaO and TiO₂, phases other than tetragonal BaTiO₃, lack of homogeneity, etc. The extent of such variations depends on the fabrication technology and these undesirable changes were ignored while studying the end properties. Hence, in the pesent study, highly pure (>99.9% pure), homogeneous and stoichiometric barium titanate was prepared by thermal decomposition of barium titanyl oxalate tetrahydrate. The ‘activity’ required for subsequent sintering of the compacts was suitably varied by calcination temperature in the range of 600°–1100°C. It was seen that when the powders were calcined in the temperature range of 800°–900°C, compacts having more than 95% of theoretical density with zero open porosity could be prepared by sintering at 1200°C. For the powders calcined at 600°–700°C or 1000°–1100°C, compacts with these physical properties were not obtained at such a low temperature of sintering. The dielectric properties were measured on the discs having more than 95% of theoretical density with zero open porosity so that the exclusive influence of calcination and sintering on the end properties could be clearly established. By judicious choice of method of powder preparation and sintering schedule, dielectric constant of the order of 14,000 could be achieved on pure barium titanate which is almost seven times the single crystal average value (≃ 2000).