PROTONIC CONDUCTION IN BA2IN2O5

Protonic conduction in Ba2In2O5 was studied by conductivity and EMF me asurements as a function of temperature and oxygen activity. Evidence for protonic conduction was found in this material in moist atmosphere s, especially at low temperatures. Three regions of protonic conductio n in the Arrhenius plot have been observed and analyzed. At low temper atures (T < 400 degrees C) the protonic conductivity is history depend ent, and the proton mobility enthalpy (Delta H-H,H-m= 0.77 eV) has bee n obtained from conductivity measurements. At intermediate temperature s between the oxygen order-disorder transition temperature (T-d = 925 degrees C) and 400 degrees C, equilibrium with moist atmospheres can b e reached. Considering the oxygen vacancy and proton formation mechani sms, the proton formation enthalpy for consuming one H2O and creating two protons Delta H-H,H-F = -0.90 eV) has been obtained. The observed proton conductivity transition at the oxygen order-disorder transition temperature directly confirms the proton formation mechanism by incor poration of H2O molecules into oxygen vacancies.