Abstract: Disclosed herein is a method of forming a single crystal film of sodium-beta"-alumina, comprising the steps of providing a single crystal substrate with one surface being arranged to minimize nucleation sites thereon, at least a portion of the substrate including alumina. A single crystal substrate is then deposited in a chamber, along with a precursor in the chamber. The precursor has a sufficient quantity of sodium species in a vapor phase and at an energy level sufficient to react with the alumina to form sodium-beta"-alumina. The precursor also includes a sufficient quantity of a stabilizing ion with a valence equal to or lower than aluminum to minimize decomposition of sodium-beta"-alumina to sodium-beta-alumina.