Oxygen pressure dependence of the ionic conductivity of iron-doped calcium titanate
Résumé
The ionic conductivity of CaTi0.9Fe0.1O3−δ was determined as functions of oxygen partial pressure and temperature, using two experimental methods: total electrical conductivity measurements by impedance spectroscopy and oxygen isotopic exchange. The data were compared with previously published results. It was demonstrated that, in contradiction with the hypothesis often assumed, the ionic conductivity is not constant in the whole oxygen pressure range. The variation of the ionic conductivity as a function of the oxygen pressure, in the domain where an additional p-type electronic conductivity is observed, was calculated for CaTi0.9Fe0.1O3−δ using our results, and for CaTi0.8Fe0.2O3−δ using data from the literature. At 900 °C, under air, a decrease of the ionic conductivity of 30% compared to the value under 10−7 bar was calculated for the CaTi0.9Fe0.1O3−δ and an increase of 100% was determined for the CaTi0.8Fe0.2O3−δ. This feature was interpreted in terms of the complex defect chemistry of iron-doped calcium titanates.