On the effect of Cd doping for Ca in La3CaBa3Cu7Oy superconducting cuprate

We report on the influence of isovalent substitution of Cd2+ for Ca2+ on the structural, electrical and magnetic properties of La3CaBa3Cu7Oy. Based on X-ray diffraction and DSC measurements, Cd can replace upto 100% of Ca ions without affecting the basic crystal structure or the formation of any impurity phases. Both Tc and oxygen content decrease monotonously with Cd content. Contrary to Y-123, the transition from the region of maximal Tc to the non-superconducting state takes place within a narrow range of oxygen content. The difference in chemical properties between Cd and Ca, as well as the observed concomitant decrease in the oxygen content, is believed to be responsible for the structural changes and suppression of superconductivity through the reduction of oxygen in the Cu–O layers when Cd replaces Ca.