Abstract: Production of thin stable films of oxy-anion-substituted silver iodide solid electrolytes, such as Ag.sub.19 I.sub.15 P.sub.2 O.sub.7, on a substrate, such films having good ionic conductivity at room temperature, by vaporizing such oxy-anion-substituted silver iodide elecytrolyte material, or a mixture of the components thereof in stoichiometric proportions, by flash evaporation of such electrolyte material at high temperature, preferably ranging from about 1,400.degree. to about 1,600.degree. C., or by RF sputtering, preferably at electrode potentials ranging from about 700 to about 900 volts, and maintaining the substrate on which the solid electrolyte film is deposited, at certain elevated temperatures, preferably ranging from about 140.degree. to about 150.degree. C.