Nonstoichiometry and relaxation kinetics of nanocrystalline mixed praseodymium cerium oxide Pr0.7Ce0.3O2-x

The oxygen deficiency and kinetics of oxygen uptake and release of nanocrystalline mixed praseodymium-cerium oxide with composition Pr(0.7)Ce(0.3)O(2-x) were investigated by combining coulometric titration and potentiometric measurements using stabilised zirconia oxygen concentration cells. The P(O(2)) versus composition isotherms indicate a two-phase region at high P(O(2)) [P(O(2)) > 0.1 bar at 560 degrees C] and a single-phase region at lower P(O(2)). The oxygen pressure dependence in the homogeneous region can be described by a power law with an exponent (-1/6), in accordance with doubly charged oxygen vacancies as majority defects. The enthalpy of I eduction amounts to (2.9 +/- 0.3) eV. The chemical diffusion coefficients are of the order of 10(-6) cm(2) s(-1) at 640 degrees C with an activation energy of approximate to 0.3 eV. The low activation energy for diffusion may be related to the high density, of interface sites in the nanocrystalline material. (C) 1999 Elsevier Science Limited. All rights reserved.