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Athermochemical Investigation of the La-Sr-Cu-O System

The perovskite related La 2‐x M x CuO 4‐y oxides substituted with alkaline earth metals were one of the first classes of high temperature superconductors discovered. Determining the thermodynamic properties is important to understand the stability and superconducting mechanism of these structures. High temperature solution calorimetry, using a molten lead borate solvent, has been performed on La 2 CuO 4 and the related Sr substituted oxides. Calorimetric measurements on CuO, La 2 O 3 and SrCO 3 yield heats of formation. A change in the trend of the heats of formation appears at Sr content 0.1, the reported orthorhombic to tetragonal transition, the onset of superconductivity and loss of oxygen.