EXAFS study at the La LIII X-ray absorption edge of superconducting materials obtained by fluorination of La2−xSrxCuO4 oxides (0≤x≤0.15)

Abstract The influence of a fluorine-gas treatment on both structural and superconducting properties of the La 2− x Sr x CuO 4 (0≤ x ≤0.1 5) solid solution has been studied. This treatment leads to the occurence of superconductivity at 40 K and 36 K for x =0 and x =0.02, respectively. In contrast, only a small change of the critical temperature is observed for x =0.10 and x =0.15 after fluorination of the compounds. Such a behaviour is consistent with the increase of the hole concentration arising from the incorporation of anionic species into the lattice. The study of the F 2 -treated La 2 CuO 4 by neutron diffraction reveals that the occupancy rate of the anionic interstitial site O(4))( 1 4 , 1 4 , 0.2646) is n =0.089(6), corresponding to the formula La 2 Cu(O,F) 4, 18 for the resulting oxyfluoride. The analysis of the EXAFS spectra recorded at the La L III -edge shows an increment of the anionic species around lanthanum ions.