Hydration Entropy and Enthalpy of a Perovskite Oxide from Oxygen Tracer Diffusion Experiments
Joe Kler, Roger A. De Souza
Abstract
Water incorporation into perovskite oxides generates protonic defects in the form of hydroxide ions. In this study, an indirect method to probe the thermodynamics of water incorporation is demonstrated. Acceptor-doped single-crystal samples of SrTiO3 were subjected to H218O/H216O exchange annealing at temperatures of 723 < T/K < 1023 at a water partial pressure of pH2O = 0.1 bar; from 18O diffusion profiles, measured by secondary ion mass spectrometry, oxygen tracer diffusion coefficients DO* were obtained. The decreased values of DO* for wet (relative to dry) conditions yielded ΔhydH = −(73 ± 15) kJ mol–1 and ΔhydS = −(148 ± 18) J mol–1 K–1 as the hydration enthalpy and entropy of SrTiO3. For T < 1023 K and this pH2O, the experiments also indicate that oxygen exchange from H2O(g) is faster than that from O2(g) (with a lower activation enthalpy) and that the surface space-charge potential is decreased under wet conditions.