It was recalled that complex perovskites of A2(B',B")O6 and A2(B',B2")O9 type, where the A-ions were 2+, the B' ions were 3+ or 2+, respectively, and the B" ions were 5+, could become good high-temperature protonic conductors when they were made non-stoichiometric by increasing the concentration of the B' ions at the expense of the B" ions. After heating in water vapour, H2O uptake occurred and protons entered the structure. The results showed that disorder favoured a higher conductivity, that the degree of order could change as a function of the non-stoichiometry and that Ba compounds always exhibited higher conductivities and lower activation energies than did the corresponding Sr compounds.

Some Factors that Determine Proton Conductivity in Nonstoichiometric Complex Perovskites. A.S.Nowick, Y.Du, K.C.Liang: Solid State Ionics, 1999, 125[1-4], 303-11