Superconductivity of the Y1-xLaxBa2Cu 8Oy system prepared in air
Résumé
The Y1-xLaxBa2Cu3Oy oxides have been investigated in order to know the influence of Y-La substitution and oxygen stoichiometry on both crystal structure and superconducting properties. The samples have been prepared in air (heating at 880°C for 24 h and annealing at 500°C for 48 h) in order to fix the oxygen partial pressure. YBa 2Cu3Oy and LaBa2Cu3O y have an orthorhombic and a tetragonal symmetry respectively. An orthorhombic to tetragonal transformation has been found for x > 0.75. All the compounds having the orthorhombic symmetry are superconductors with critical temperature decreasing from 88 K to 46 K as x increases in the composition range 0 ≤x≤0.75. Those with the tetragonal symmetry do not exhibit a superconducting transition as for example LaBa2 Cu3Oy. However this last compound prepared under pure oxygen atmosphere has been found to be superconducting (Tcr = 70K).
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