Thermodynamic description of the nonstoichiometric defect structure in Ce1-xZrxO2 solid solution powders

Equilibria between gaseous oxygen (from 870 to 20 000 Pa) and several high surface area Ce1-xZrxO2 powders (0 less than or equal to x less than or equ al to 0.36) were studied by means of thermogravimetry in order to get a bet ter insight into the nature and behaviour of the point defects in these sol id solutions. By measuring the weight changes between two different oxygen pressures, we could obtain the variations of the oxygen vacancy concentrati on at the surface of the solutions as a function of the oxygen pressure and zirconium concentration. The anionic sublattice was shown to follow an ide al thermodynamic behaviour, the oxygen vacancy concentration bring proporti onal to P-O2(-1/6). By comparing the experimental and theoretical variation s of the oxygen vacancy concentration versus the zirconium concentration, w e found that the cationic sublattice was well described by a nonideal (regu lar) model in which the activity coefficients of the structural elements Ce -Ce(x), Zr-Ce(x) and of the associated defect (Zr-Ce, Ce-Ce')' are differen t from 1. (C) 2000 Elsevier Science BN. All rights reserved.