Infrared And Raman-Spectroscopic Studies Of Superconducting Electrochemically Oxidized La2cuo4

Infra-red spectra of electrochemically oxidized La2CuO4+delta recorded at various temperatures between 20-degrees-C to 250-degrees-C and the Raman spectrum at room temperature have been analyzed and compared with those of stoichiometric La2CuO4 and strontium substituted La1.85Sr0.15CuO4. It has been shown that oxygen enriched La2CuO4+delta exhibits a Raman spectrum characteristic of a highly distorted orthorhombic structure due to oxygen insertion. The thermal variation of the IR spectra as well as the TGA and magnetic data can be explained by an irreversible transition to stoichiometric La2CuO4 above 220-degrees-C due to oxygen release. This loss of oxygen results in a decrease of hole concentration in the material inducing a strong intensity enhancement of an IR phonon mode around 680 cm-1. It is also corroborated that the excess of oxygen is located in the La2O2 planes of the structure.