The defect structure and transport properties of complex perovskites having the general formula, Sr3(Sr1+xNb2-x)O9-3x/2, were studied by using thermogravimetry, alternating-current conductivity and transport number measurements. The samples ranged in composition from Sr3(SrNb2)O9 to Sr3(Sr1.5Nb1.5)O8.25. Thermogravimetry was used to measure the uptake of water, and the greatest reversible water uptake was found for the end member: Sr3(Sr1.5Nb1.5)O8.25. The total conductivity of Sr3(Sr1.4Nb1.6)O8.4, as a function of O partial pressure and temperature, was fitted to a model which was based upon Sr-acceptor defects which were compensated by doubly-charged O vacancies and protons. The partial conductivities which were found from transport number measurements supported the predicted results. It was found that O-ion conductivity predominated at high temperatures, while protonic conductivity predominated below 550C; at ambient humidities. The enthalpy and entropy, for the reaction of H2O with O vacancies to form protons, were found to be –160kJ/mol and -l66J/Kmol, respectively, for this sample. The O-ion and proton conductivities increased with Sr content. The increase far exceeded the expected behaviour.

Protons in Sr3(Sr,Nb)2O9 Perovskite. R.Glockner, A.Neiman, Y.Larring, T.Norby: Solid State Ionics, 1999, 125[1-4], 369-76