Complex oxides, oxide-ion conductors, oxide-ion conducting films and electrochemical cells

An object of the present invention is to provide a novel complex oxide applicable as an oxideion conductor. The complex oxide according to the present invention has a basic composition of (SmA) (AlB) O 3. In the formula, "A" represents one or more element selected from the group consisting of barium, strontium and calcium; "B" represents an element selected from the group consisting of magnesium, iron and cobalt; x = 0.10 to 0.30; and y = 0 to 0.30.