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Superconducting La2CuO4+x prepared by oxygenation at high pressure. A Raman scattering study
Superconducting crystals of La2CuO4+x prepared by high-pressure oxygenation have been analyzed by Raman spectroscopy. A direct comparison of the role of excess oxygen was made by examining the same crystals with and without excess oxygen. La2CuO4+x, like non-superconducting La2CuO4.0, is found to have a soft phonon that derives an orthorhombic to tetragonal phase transition. In both its tetragonal and orthorhombic forms, La2CuO4+x has a phonon peak at 630 cm-1 that is absent in La2CuO4.0. The frequency of this peak is suggestive of a peroxide-like species in La2CuO4+x. Surprisingly, the Ag phonons of La2CuO4.0 and La2CuO4+x occur at essentially the same frequency. While La2CuO4.0 has a well-defined peak from double-magnon scattering, no well-defined double-magnon scattering is observed in La2CuO4+x, even in its phase-separated form.