SUPERCONDUCTIVITY OF THE LA3.5-X-YRYCA2XBA3.5-XCU7OZ SYSTEM (R = GD, ND, AND DY)

The structural and superconducting properties of single phase La3.5-x- yRyCa2xBa3.5-xCu7Oz (0 less than or equal to x = y less than or equal to 0.70) (LRCB with R = Gd, Nd and Dy) compounds with tetragonal tripl e-perovskite structure are investigated using X-ray diffraction, resis tivity, AC susceptibility and oxygen-content measurements. Increasing Ca and Gd substitution for La and Ca for Ba resulted in a decrease in unit cell axes and an increase in oxygen stoichiometry. Samples with 0 .2 less than or equal to x = y less than or equal to 0.70 are supercon ducting and T-c(R=0) is between 31 and 79 K. With increasing x = y, bo th the hole concentration in the Cu2-O layers and T-c(R=0) increase to a maximum value of 0.313 and 79 K at x = y = 0.6, respectively. A cor relation between the T-c and the hole concentration is suggested. Simi lar superconducting behaviour has been observed for R = Nd and Dy in L RCB compounds. (C) 1997 Elsevier Science B.V.