Hole Concentration Compensation Effect and Superconducting Properties of Nd1+xBa2-xCu3O7-δ

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Abstract
The superconducting transition temperature T c and normal-state resistivity have been investigated as a function of x for the Nd1+x Ba2-x Cu3O7-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.