ANOMALOUS THERMAL EFFECT OF Y_1-xCa_xBa₂Cu₃O_y

It is found in oxygen there are a weight loss and an endothermal anomaly in compound of Y_1-xCa_xBa₂Cu₃O_y starting at about 320 °C, while in nitrogen at about 370 °C and a mixed atmosphere, N₂(50%)+O₂(50%), at about 350 °C. The results are different from those in undoped YBa₂Cu₃O_y and some doped systems. It is suggested that Ca prefers a sixfold coordination, which causes the oxygen loss in Cu(2)-O plane and the weight and heat anomalies at different temperature in different atmospheres. The oxygen loss in Cu(2)-O plane is also responsible for T_c suppression in Y_1-xCa_xBa₂Cu₃O_y.