The structure, conductivity and water uptake of the O-deficient compound Ba4Ca2Nb2O11 were investigated. It was found to crystallize in the cryolite structure, with a = 8.4449Å. The compound could be fully hydrated up to a maximum water content of about 1mol of H2O per mol of Ba4Ca2Nb2O11. This process was accompanied by a reversible phase transformation due to the formation of hydrate-like compound. In wet air, the temperature dependence of total conductivity exhibited a different behavior because of a change in proton transport mechanism: small local maximum as a result of phase transformation (350C), linear relationship with an activation energy of 0.55eV at 350 to 230C, and 1.02eV at lower temperatures.

Proton and Oxygen-Ion Conductivity of Ba4Ca2Nb2O11. I.Animitsa, A.Neiman, N.Kochetova, B.Melekh, A.Sharafutdinov: Solid State Ionics, 2003, 162-163, 63-71