The oxygen and proton conductor Ba2In2O5: Thermogravimetry of proton uptake

The oxygen ion and proton conductor Ba2In2O5 was investigated by thermograv imetry. Proton concentrations were obtained as a function of temperature an d applied water vapor pressure. Two competing thermodynamic models were app lied to the solubility data. For both models, proton uptake is governed by: (H2O)(gas) + V-O(..) + O-O(x) double left right arrow 2OH(O)(.). The first one considers a temperature dependent O-vacancy concentration, the second a constant O-vacancy concentration and trapping. The instability of Ba2In2O 5 in humid atmospheres below 300 degrees C resulting in a new high proton-c ontent phase HBaInO3 is discussed. The chemical diffusion of water in Ba2In 2O5 was measured as a function of temperature. These data are required to a ssess penetration times of protons into initially dry bulk samples of Ba2In 2O5. (C) 1998 Elsevier Science B.V. All rights reserved.