STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF R1-XCAXBA2CU3O6-LESS-THAN-DELTA-LESS-THAN-1)(DELTA (R = Y, ER, GD, EU O)

The influence of oxygen content delta on the superconducting critical temperature T-c and the crystal structure of R1-xCaxBa2Cu3O6+delta(R = Y, Er, Gd, Eu; x = 0.0-0.2) has been studied by resistivity and X-ray powder diffraction measurements. All as-grown compounds with x = 0.2 have delta similar to 0.83 and are in the orthorhombic phase. Their op timum T(c)s are around 85 K. Both the compounds with R= Y and Eu show the plateau in T-c vs. delta (T-c,T-pl) at 60 K in the tetoragonal pha se. For the compounds with R = Gd and Er the plateau appeared in the t etragonal phase at 20 and 40 K, respectively. The value of T-c,T-p) fo r R = Gd increases from 20 to 60 K with decreasing Ca content x. It is shown that the values of T-c,T-pl can be correlated with the c-axis l attice parameters. Furthermore, we provide the correspondence of the i ncrease in T-c above 60 K with orthorombicity over the present kinds o f R. (C) 1998 Published by Elsevier Science B.V. All rights reserved.