PROTON CONDUCTOR, ELECTROLYTE MEMBRANE, MEMBRANE ELECTRODE ASSEMBLY, ELECTROCHEMICAL CELL AND FUEL CELL STACK

A proton conductor of the present disclosure includes a compound represented by the chemical formula BaZrYbScO. The chemical formula satisfies 0 < x < 0.5, 0 < y < 0.5, (x + y) < 0.5, and 0 < δ < 0.5.