The conductivity of the complex perovskite, Ba3Ca1.18Nb1.82O9, was investigated by repeatedly charging identical samples with increasing amounts of water. It was found that, at temperatures below 300C, the bulk conductivity increased linearly with the frozen-in proton concentration. The proton mobility which was deduced from the data had an activation energy of 0.53eV, and agreed with the results of quasi-elastic neutron

scattering. A significant grain boundary impedance was found. At temperatures below 500C, the grain-boundary conductivity was much lower than the proton conductivity in the grain interior and was dominated by electron holes; even in wet samples. Under equilibrium conditions, above 700C, the ionic transport numbers which were calculated from the results of the impedance measurements agreed with those of electromotive force measurements. It was concluded that excellent proton conduction was to be found in the grain interiors, while the grain-boundary conductivity required further investigation.

The High Temperature Proton Conductor Ba3(Ca,Nb)3O9. H.G.Bohn, T.Schober, T.Mono, W.Schilling: Solid State Ionics, 1999, 117[3-4], 219-28