These materials have a conductivity of at least 1.0x10-5 S/cm at 300K, which allows them to work in room temperature sodium based storage devices. The high conductivity at room temperature is achieved through the materials’ spinel structure of the general formula AB2C4 wherein anions C are arranged in a close-packed cubic and cations A and B occupy some or all of the octahedral and tetrahedral sites in a lattice. This structure provides good three-dimensional ion transport. These materials are produced by mixing powder combinations and then heat treating them up to 700oC. There is an inverse relationship between the cooling rate and the conductivity of the material. As such, the preferred cooling rate is no greater than 0.2oC/min.