. "t metal selected from the group consisting of Al, Ga, In, and Tl, A is a metal oxide, X is at least one halogen selected from the group consisting of Cl, Br, and I, each of X???, X???, and X?????? is at least one halogen selected from the group consisting of F, Cl, Br, and I, a is a number satisfying 0???a???2, b is a number satisfying 0???b???10???2, c is a number satisfying 0???c???10???2, and a" . . .