Physicochemical properties of rock salt-type ordered Sr_2MMoO_6 (M = Mg, Mn, Fe, Co, Ni) double perovskites

摘要

B-site rock salt-type ordered Sr_2MMoO_6 (M=Mg, Mn, Fe, Co, Ni) oxides have been systematically investigated in terms of their crystal structure, oxygen non-stoichiometry, transport properties, thermal expansion and chemical stability. Structural evolution on temperature of the studied materials was interpreted on a basis of octahedra rotation, with 74/m-> Fm-3m phase transition. In the case of P2_1-> I4/m transformation recorded for Sr_2MnMoO_6, a region of coexistence of two phases was observed. The Fe-containing compound was found to possess very high electrical conductivity, around 1000 S cm~(-1) in 5 vol.% H_2 in Ar, and small negative Seebeck coefficient. Studies show that Mn- and Fe-containing compounds are stable only in reducing conditions, Co- and Ni-containing ones are stable only in oxidizing conditions, while Sr_2MgMoO_6 remains stable in a wide range of oxygen partial pressures. Recorded power density of a button-type SOFC with Sr_2FeMoO_6,-based anode was 0.32 W cm~(-2) at 900 °C.