The new perovskite oxide Sr3Ca1+xZr(1-y)-x/2Ta(1+y)-x/2O8.5-[(5x-2y)/4] belonged to the class of complex perovskites of general formula A3(B',B'')3O9-δ. The specific composition Sr3CaZr0.5Ta1.5O8.75 was already reported as a promising proton conducting material in a wet H atmosphere. The extent of vacancy formation and hence degree of hydration in these systems was quite extensive for a perovskite lattice. This seemed to be related to the presence of the polarizable Ca2+ cation on the B site. Here, Ca was replaced by varying amounts of Zn. The extent of hydration was found to decrease rapidly with Zn substitution, as did the extent of proton conductivity. As very little water uptake was observed for compositions with more than 25% of Ca2+ replaced by Zn2+, this effect was not simply statistical. Instead, it was supposed that extended interactions due to the polarizable Ca2+ ions facilitated water uptake. It was proposed that mixed oxides such as Sr3CaZr0.5Ta1.5O8.75+yH2O were effectively under-doped in terms of protonic conductivity at low temperatures in wet atmospheres.

Sr3Ca1-xZnxZr0.5Ta1.5O8.75 - a Study of the Influence of the B-Site Dopant Nature upon Protonic Conduction. C.Savaniu, J.T.S.Irvine: Solid State Ionics, 2003, 162-163, 105-13