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 nanocrys talline mixed praseodymium-cerium oxide with composition Pr0.7Ce0.3O2-x wer e investigated by combining coulometric titration and potentiometric measur ements using stabilised zirconia oxygen concentration cells. The P(O-2) ver sus 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). Th e oxygen pressure dependence in the homogeneous region can be described by a power law with an exponent (-1/6), in accordance with doubly charged oxyg en 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 Else vier Science Limited. All rights reserved.