Superconductivity in Ni substituted Bi 2Ca 1Sr 2Cu 2−xNi xO y

Abstract

The effect of partial substitution of Ni in place of Cu in Bi 2Ca 1Sr 2Ni x Cu 2− x O y has been systematically investigated for 0⩽ x⩽0.2. The XRD of the samples confirms them to be of single phase. The superconducting critical temperature T c monotonically decreases with Ni concentration; the rate of T c decrease is around 2.5 K/% of the nominal substitution. All the samples have been subjected to XPS studies. The results show that Ni is incorporated in the lattice in the divalent state with Ni-O bonds substituting for the Cu-O bonds while keeping Bi-O, Sr-O and Ca-O bonds intact. Change in the Ni content does not seem to affect the valence state of Cu. The question of T c decrease with Ni substitution is examined.