Fluorite structure type ceria type solid electrolyte

A defective fluorite structure solid electrolyte of the following formula (2):

• {(M.sub..alpha. A.sub.a).sub.x Ce.sub.1-x }O.sub.2-y ( 2)
• wherein M is a trivalent rare earth element other than Ce, A is a monovalent alkali metal or a bivalent alkaline earth metal, and .alpha., a, x and y are 0.4<.alpha.<1, 0<a<0.1, 0.2<x<0.5 and 0<y<0.26, respectively.

A defective fluorite structure solid electrolyte of the following formula (3):

• {(M.sub.1-a A.sub.a).sub.x (Ce.sub.1-b B.sub.b).sub.1-x }O.sub.2-y( 3)
• wherein M is a trivalent rare earth element other than Ce, each of A and B is a monovalent alkali metal or a bivalent alkaline earth metal, provided A.noteq.B, and a, x, b and y are 0<a<0.6, 0.1<x<0.4, 0<b<0.4 and 0<y<0.8, respectively.

A defective fluorite structure solid electrolyte of the following formula (4):

• {(M.sub..alpha. A.sub.a).sub.x (Ce.sub..beta. B.sub.b).sub.1-x }O.sub.2-y( 4)
• wherein M is a trivalent rare earth element other than Ce, each of A and B is a monovalent alkali metal or a bivalent alkaline earth metal, provided that A.noteq.B, and .alpha., a, x, .beta., b and y are 0.4<.alpha.<1, 0<a<0.1, 0.1<x<0.4, 0.6<.beta.<1, 0<b<0.1 and 0<y<0.41, respectively.