Synthesis and superconductivity of PbBaSrY1−xCaxCu3O7

Superconducting PbBaSrY 1− x Ca x Cu 3 O 7 with a maximum T c onset at 65 K was synthesized. Single-phase materials were obtained for 0 ⩽ x ⩽ 0.25 by sintering in a 1% O 2 -N 2 gas at 750–830°C and quenching from 785°C. Superconductivity appeared for x ⩾ 0.15 and T c increased with increasing Ca content. PbBaSrY 0.7 Ca 0.3 O 7 was confirmed to achieve zero resistance at 37 K with about 45% bulk superconductivity. Superconductivity was considered to occur by hole introduction in CuO 2 sheets by substituting Y 3+ with Ca 2+ , the same mechanism as in Pb 2 Sr 2 Y 1− x Ca x Cu 3 O 8 .