High temperature superconductivity in SmBa2Cu3O 7-x : transport properties and effect of pressure

Sintered powders of SmBa 2 Cu 3 O 7−x have been prepared and characterized. The physical properties, superconducting temperature transition, up to 92 K, magnetic susceptibility, electrical resistivity and thermopower have been studied as a function of the preparation conditions and therefore of oxygen stoichiometry. The upper critical field has been estimated from resistivity measurements in fields up to 8 T and the slope (dBc 2 /dT) Td c found to be close to 4 T K −1 for the highest T c samples. Studies of the electrical resistivity under hydrostatic pressures up to 18 kbar show an increase of T c under pressure with dT c /dp∼0.5 K kbar −1 . Finally measurements of voltage-current characteristics indicate that either Josephson junctions or superconductor-insulator-normal metal junctions can be found inside the samples, as expected in inhomogeneous materials Mesures de la conductivite electrique, du pouvoir thermoelectrique et de la susceptibilite magnetique; influence des conditions de preparation et donc de la stœchiometrie en oxygene. Effets de la pression et des conditions de preparation sur la temperature de transition supraconductrice; estimation du champ critique et de la pente (dHc 2 /dT) Td c. Mesures de la caracteristique I-V et mise en evidence de l'existence de jonction de type Josephson ou SIN