SYNTHESIS AND SUPERCONDUCTING PROPERTIES OF CA1-XRXBALACU3O7-DELTA (R=CE AND ND) SYSTEMS

X-ray diffraction analysis of the series Ca1-xCexBaLaCu3O7-delta shows that the Ce4+-ion has a limited solubility in the parent compound, vi z. x<0.15. Substitution of Ce for Ca causes a sharp fall in the superc onducting transition temperature (T(c)) from 72 K for x=0.0 to 41 K fo r x=0.15, as observed from the electrical resistivity and AC-susceptib ility data. On the other hand, the Nd3+-ion has a wider range of solid solubility in Ca1-xNdxBaLaCu3O7-delta (up to x less-than-or-equal-to 0.4) and substitution of Nd leads to only a marginal decrease of T(c). For instance, the value of T(c) was observed to be as high as 65 K fo r x=0.3. However, the T(c) decreased sharply for an Nd-content beyond this limit, viz. x>0.3, resulting in a total loss of superconductivity for x>0.6. The XRD-patterns of Ca1-xNdxBaLaCu3O7-delta for x>0.4 show a significant broadening of peaks corresponding to large 2theta value s, the patterns becoming increasingly similar to that of La-3 36 phase , as the x-value approaches unity.