Investigations on the defect chemistry and the sintering of barium titanate ceramics by oxygen coulometry

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 described. The measuring principle is based on two identical solid electrolyte circonia cells with two electrode pairs both for measuring of the oxygen partial pressure and for oxygen pumping. Three different oxygen exchange processes of the samples could be detected. (1) The oxygen exchange due to the change of the equilibrium temperature at a fixed oxygen partial pressure, which is caused by the change of the concentration of oxygen vacancies. (2) The oxygen exchange which is related to the valence change of Mn-Ti during the change of the ambient atmosphere. The data are consistent with the assumption that manganese occurs as Mn3+ at an oxygen partial pressure of 2.4 Pa and a temperature of about 1400 degreesC. (3) During the sintering of donor-doped barium titanate ceramics, oxygen expelling processes were detected which are related to the incorporation of the donor into the lattice. In the case of a doping level of 0.5 mol% La, the estimated amount of expelled oxygen is less than expected for exclusive electronic donor compensation. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.