Ceramics exhibiting both electronic and ionic conductivities can be obtained by doping highly oxygen conducting matrices with multivalent cations. These materials allow oxygen transport to occur under open circuit conditions driven by an oxygen chemical potential gradient only. In the present work, equations are developed which express this oxygen flux as a function of environmental and material variables. For small PO2 gradients, the oxygen flux is maximized when tO2- = te- = 0.5. To treat the case of significant PO2 gradients, a more general analysis has been carried out using a model material system, ZrO2-Y2O3-MO2, where M is Ce or Ti. The extrinsic electron conductivity due to the multivalent dopant exhibits a maximum when plotted either as function of temperature or PO2. As a result, an inflexion point is observed at a critical oxygen pressure, PcO2 in the curve describing oxygen flux through the material as a function of the environmental PO2. Below PcO2, the oxygen flux rapidly approaches a saturation value, JmaxO2-. Both PcO2 and JmaxO2- are shown to be functions of temperature and material composition. The variation of PO2 through the material is also discussed.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics