This proposal is aimed at the synthesis of new quaternary oxides in molten hydroxide fluxes, and a study of the reaction conditions that favor certain structural features in the solids as they crystallize. The development of practical synthetic routes that result in materials which exhibit specific properties and which are therefore more amenable to processing is the ultimate goal of the project. Initial studies will focus on the preparation of new, high-temperature superconducting quaternary metal cuprates, bismuthates, and niobates using molten alkali metal and/or alkaline earth metal hydroxides as solvents.