THE EFFECTS OF CHEMICAL SUBSTITUTIONS ON THE (PB, CD)-1212 SUPERCONDUCTING CUPRATES

The effects of different substitutions on (Pb0.5Cd0.5)Sr2(Y0.5Ca0.5)Cu2O7 have been investigated. For (Pb0.5Cd0.5)Sr2(Y1-xCax)Cu2O7 (0.0 less-than-or-equal-to x less-than-or-equal-to 1.0), an anomalous variation of lattice constants with x is observed, and a sharp increase in T(c) occurs when x increases from 0.4 to 0.5. For (Pb0.5Cd0.5)Sr2-y(Y0.5+yCa0.5)Cu2O, (-0.2 less-than-or-equal-to y less-than-or-equal-to 0.3), as yttrium content increases the phase purity increases, and both the a and c lattice constants decrease. The superconducting properties deteriorate as y deviates from 0.0. For (Pb0.5Cd0.5)Sr2-z(Y0.5Ca0.5+z)Cu2O7 (-0.2 less-than-or-equal-to z less-than-or-equal-to 0.2), both the a and c lattice constants decrease as z increases. The superconducting properties deteriorate as z deviates from 0.0, although the effect is very small. From the T(c) results obtained in the three series, the conclusion can be reached that the yttrium content in the (Y, Ca) sites is a key factor in controlling the superconducting properties of the (Pb, Cd)- 1 212 phase.