Raman probing of thermally induced effects on La2−xSrxCuO4 single crystals

Abstract We have investigated the effects of long oxygen annealing of flux grown La 2− x Sr x CuO 4 single crystals, using their Raman scatterin as a probe. The as-grown crystals display very weak Raman activity, whereas the annealed crystals show three well defined Raman peaks which disappear upon polishing a layer of ∼10 μm from the surface, indicating a low oxygen diffusion rate from surface to bulk. The Raman scattering exhibited by the annealed crystals is attributed to surface defects or/and new phases formed during the annealing. After annealing, the crystals were found to display superconductivity at 8 K.