Measuring oxygen diffusion and oxygen surface exchange by conductivity relaxation

For materials that are predominantly electronic conductors and possess a ma terials property that changes with oxygen partial pressure then a 'relaxati on' technique may be used to measure oxygen transport behaviour. Perhaps th e simplest to implement is electrical conductivity relaxation. For many mix ed conducting materials a change in the oxygen partial pressure will result in a corresponding change in the electrical conductivity of the material d ue to, primarily, a change in the concentration of charge carriers. If the ionic conductivity of a material is significantly less than its electronic conductivity then the time for this change to propagate throughout the mate rial is almost exclusively controlled by the movement of ionic species. Thi s change or 'relaxation' can be modelled and oxygen diffusion coefficients and surface exchange coefficients can be extracted from the data. This pape r will discuss the measurement of oxygen transport in mixed-conducting cera mic oxides using the conductivity relaxation technique. Emphasis will be pl aced on the analysis of the 'relaxation' profile and the problems associate d with determining oxygen diffusion coefficients and oxygen surface exchang e coefficients simultaneously.. (C) 2000 Elsevier Science B.V. All rights r eserved.