Investigation of barium titanate ceramics by oxygen coulometry

摘要

The application of the oxygen coulometry method on the investigation of the defect chemistry and the sintering process of donor- and acceptor-doped barium titanate ceramics is introduced. The measuring device is based on two identical ZrO{sub}2 Nernst cells which are used both for the determination of the oxygen partial pressure and for the pumping of oxygen. Several examples for the application of the method are presented. (1) The measurement of the change of the equilibrium oxygen vacancy concentration with respect to a temperature change at a fixed oxygen partial pressure: (2) The investigation of the change of the valency state of acceptor-type 3d transition elements in dependence on the ambient oxygen partial pressure. It is shown that Mn{sub}(Ti) occurs as Mn{sup}3+ at an oxygen partial pressure of 2.4 Pa and a temperature of about 1400°C. (3) The oxygen release during the sintering of donor-doped BaTiO{sub}3 has proven that the incorporation of at least a partial amount of the donor dopant takes place only during the anomalous grain growth. This supports Drofenik's model on the doping anomaly of barium titanate ceramics. In the whole doping range of a maximum amount of 5 mol% La{sub}(Ba), the estimated amount of expelled oxygen is less than expected for exclusive electronic donor compensation.