Protonic conduction was studied, by means of conductivity and electromotive force measurements, as a function of temperature and O activity. Evidence of protonic conduction was found in moist atmospheres; especially at low temperatures. Three regions of protonic conduction were identified in the Arrhenius plot. At temperatures below 400C, the protonic conductivity was history-dependent and a mobility enthalpy of 0.77eV was deduced from conductivity data. At temperatures between the O order-disorder transition temperature (925C) and 400C, equilibrium with moist atmospheres could be established. By analyzing the O vacancy and proton formation mechanisms, a proton formation enthalpy (0.90eV) was estimated for the consumption of one H2O molecule and the creation of 2 protons. An observed proton conductivity transition at the O order-disorder transition temperature confirmed that protons were formed by the incorporation of H2O molecules into O vacancies.

G.B.Zhang, D.M.Smyth: Solid State Ionics, 1995, 82[3-4], 153-60