Rare-earth ionic radius dependence of superconductivity in Pr-substituted and oxygen deficient R 1− xPr xBa 2Cu 3O 7− y

Abstract

The suppression effect of superconductivity by Pr substitution correlates strongly with that by oxygen deficiency in the R 1− x Pr x Ba 2Cu 3O 7− y system, where R is Yb, Y, Ho, Dy, Gd and Nd. The larger the value of x C, the Pr content at which superconductivity disappears, the larger the value of y C, the oxygen deficiency at which superconductivity disappears. The decreasing rate in T C by Pr substitution (−d T C/d x) decreases with decreasing ionic radius of a rare-earth ion for the Ortho-I phase ( T C>90 K for x=0) and also with decreasing oxygen concentration (7− y). The −d T C/d x for the smaller rare-earth ions (R=Yb, Y, Ho and Dy) are nearly independent of ionic radius for the Ortho-II phase ( T C=60 K for x=0). The Pr content dependence of T C in (Y 0.625La 0.375) 1− x Pr x Ba 2Cu 3O 7− y , average rare-earth ionic radius of which is equal to that of Gd, coincides well with that in the Gd 1− x Pr x Ba 2Cu 3O 7− y . The weakened T C-suppression by Pr in the case of the smaller rare-earth ions is explained by considering the hole transfer effect from the Cu(1)O chain toward the Cu(2)O 2 plane according to the difference in ionic radius between the rare-earth ions and Pr ion.