Variation of Superconducting Properties with Hole Concentration in the Solid Solution Systems of Sm1+xBa2-xCu3O7-δ and Eu1+xBa2-xCu3O7-δ

Abstract

Superconducting transition temperatute T _c and the normal state resistivity of Sm_1+x Ba_2-x Cu₃O_7-δ and Eu_1+x Ba_2-x Cu₃O_7-δ are investigated by changing x in the range of 0∼0.40. According to the X-ray powder diffraction at room temperature combined with the Rietveld method, all the samples are single phase. For both compound systems, T _c of the samples with x=0 and 0.05 is above 90 K and decreases monotonically with x, and the compounds become semiconducting at x=0.40. The variation of T _c with x is insensitive to orthorhombic-tetragonal phase transition at around x=0.20. These results are very similar to those of Nd_1+x Ba_2-x Cu₃O_7-δ reported in a series of recent papers by the present authors, where it has been proposed that T _c has a simple correlation with hole concentration. This also suggests that a hole concentration compensation effect by excess trivalent Ln ions substituted for divalent Ba ions commonly occurrs in Ln_1+x Ba_2-x Cu₃O_7-δ (Ln=Nd, Sm and Eu).