Hole Concentration Compensation Effect and Superconducting Properties of Nd_1+xBa_2-xCu₃O_7-δ

Abstract

The superconducting transition temperature T c and normal-state resistivity have been investigated as a function of x for the Nd 1+ x Ba 2- x Cu 3 O 7-δ system, whose crystal structures have been determined at room temperature by X-ray powder diffraction combined with the Rietveld method. T c of the samples with x =0 and 0.05 is above 90 K, which decreases monotonically with x except for around x =0.25∼0.30 ( T c ≃35 K) and the sample becomes semiconducting at x =0.40. The orthorhombic distortion of the compounds decreases with x and the compound becomes tetragonal at x =0.20. The variation of T c with x is insensitive to the orthorhombic-tetragonal phase transition. A correlation of T c with hole concentration in copper-oxide-type superconductors is discussed based on a possible hole concentration compensation effect of excess Nd.