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New K2NiF4-type superconductors obtained by halogenation treatment

Nouvelles phases supraconductrices de structure type K2NiF4 obtenues par méthodes d'halogénation

Abstract : The effect of chlorine or fluorine gas treatment on both structural and superconducting properties of series of compounds deriving from the La2CuO4-type structure has been investigated. When La2CuO4 is treated under 6 bar Cl2-gas at 300°, a decrease of the orthorhombic distorsion (b-a) occurs. The incorporation of oxygenated species into the lattice is corroborated by weight uptake, increase of c-parameter, neutron diffraction refinement. The starting semiconducting oxide is transformed to a superconducting material below 32K.
Several next superconducting phases been obtained by fluorination treatmens, such a La1.85-xNdxSr0.15CuO4 and La2-x-yNdxSryCuO4. For instance in La1.85-xNdxSr0.15CuO4, the whole range of compositions of the La2CuO4 type solid solution (0 < x < 1) becomes superconducting after fluorination. The occurrence of superconducting behavior has been ascribed to the suppression of the low temperature phase transition (LTO<->LTT) after fluorination. Of course, the fluorination treatment influences both structural and superconducting properties of all La2-x-yNdxSryCuO4 solid solution.