Growth and thermogravimetric study of Pb2Sr2R1−xCaxCu3O8+δ (R=Y, Tb) single crystals

Single crystals of Pb2Sr2R1−xCaxCu3O8+δ (R=Y, Tb) superconductor were grown from PbO-NaCl flux. The Ca content was determined by means of EDX method to vary in the range 0.3-0.5. The superconducting transition temperature was found to be close to the optimal value of 70-80 K. The intergrowths with another superconducting perovskite (Pb,Cu)Sr2(Y,Ca)Cu2O7 of Tc ≈ 60 K was observed for Y-based crystals, what resulted in a double transition observed frequently in magnetic measurements. This tendency has not been found for Tb-based crystals which usually showed more sharp transitions. Thermogravimetric experiments showed that the oxidation process of Pb2Sr2R1−xCaxCu3O8+δ single crystals proceeds in two steps. The first one corresponds to Cu1+ oxidation (500-550 °C for both R=Y and Tb), the second could be attributed to lead oxidation (830-870 °C for R=Y and 80-100 °C lower for Tb-based compound).