A method for preparing a superconductor oxide film, comprising the steps of: depositing a first precursor solution onto a substrate to form a precursor film, the first precursor solution comprising precursor components to a rare earth-alkaline earth metal-transition metal oxide comprising a salt of a rare earth element, a salt of an alkaline earth metal, and a salt of said transition metal in one or more solvents, wherein at least one of the salts of the rare earth element and the alkaline earth element is a fluoride-containing salt, and wherein the ratio of the transition metal to the alkaline earth metal is greater than 1.6; and treating the precursor film to form a rare earth-alkaline earth metal-transition metal oxide superconductor film, the treatment comprising: treating the precursor film to form an intermediate metal oxyfluoride film including the rare earth, the alkaline earth metal, and the transition metal of the first precursor solution; and heating the intermediate metal oxyfluoride film to form the rare earth-alkaline earth metal-transition metal oxide superconductor wherein the overall ratio of the transition metal to the alkaline earth metal in the superconductor film is greater than 1.6, wherein the ratio of the transition metal to the alkaline earth metal at an interface between the substrate and the intermediate metal oxyfluoride film is about 1.5, and wherein the overall thickness of the oxide superconductor is greater than about 0.8 μm. depositing a first precursor solution onto a substrate to form a precursor film, the first precursor solution comprising precursor components to a rare earth-alkaline earth metal-transition metal oxide comprising a salt of a rare earth element, a salt of an alkaline earth metal, and a salt of said transition metal in one or more solvents, wherein at least one of the salts of the rare earth element and the alkaline earth element is a fluoride-containing salt, and wherein the ratio of the transition metal to the alkaline earth metal is greater than 1.6; and treating the precursor film to form a rare earth-alkaline earth metal-transition metal oxide superconductor film, the treatment comprising: treating the precursor film to form an intermediate metal oxyfluoride film including the rare earth, the alkaline earth metal, and the transition metal of the first precursor solution; and heating the intermediate metal oxyfluoride film to form the rare earth-alkaline earth metal-transition metal oxide superconductor treating the precursor film to form an intermediate metal oxyfluoride film including the rare earth, the alkaline earth metal, and the transition metal of the first precursor solution; and heating the intermediate metal oxyfluoride film to form the rare earth-alkaline earth metal-transition metal oxide superconductor wherein the overall ratio of the transition metal to the alkaline earth metal in the superconductor film is greater than 1.6, wherein the ratio of the transition metal to the alkaline earth metal at an interface between the substrate and the intermediate metal oxyfluoride film is about 1.5, and wherein the overall thickness of the oxide superconductor is greater than about 0.8 μm.