Sintering and Oxygen Transport in Ce0.8Pr0.2O2 − δ: A Comparative Study of Mn and Co Oxide Additives

Abstract

Minor additions of manganese oxide and cobalt oxide are both shown to be good sintering aids for , a promising ceramic membrane material with comparable values of partial oxygen-ionic and electronic conductivities, to offer dense ceramics with submicron grain sizes under . Transmission electron microscopy and X-ray energy dispersive spectroscopy suggest the transition-metal oxide addition to be located in the grain boundary regions. The smallest grain size is observed in the case of materials with Mn additions. Whereas the addition of cobalt oxide radically improves the transport properties of , boosting the level of electronic conductivity by two to three times and leaving the ionic conductivity intact, the addition of manganese oxide is shown to be detrimental, increasing the activation energy for ionic conductivity while offering no benefit to electronic conductivity. These characteristic transport properties impact on levels of oxygen permeation. The flux is significantly improved in the case of Co additions due to an increased ambipolar conductivity and improved oxygen surface kinetics, whereas no improvement in oxygen permeation flux is observed for Mn additions in comparison to the base composition . It has been suggested that a very slight increase in solubility of the transition oxide addition in the grain bulk in the Mn-doped case may offer an explanation of the resultant properties.