Effect of annealing on properties of bismuth based high T_c superconductors

A novel method to increase the amount of the 110 K phase in the Bi-Sr-Ca-Cu-O system was examined. After the sample with composition of Bi₂Sr₂CaCu₂O_x had been calcined, it was soaked in ethanol containing copper acetate and calcium acetate, the amounts of which were determined to give the composition of Bi₂Sr₂Ca₂Cu₃O_y after sintering. Subsequently, annealing at about 400 °C was conducted to examine the stability of the 110 K phase. The sample containing mainly the 80 K phase and a small amount of the 110 K phase showed an increase in the amount of the 110 K phase while that containing only the 80 K phase showed no change. Therefore, it is presumed that the 110 K phase may grow when the excess calcium and copper coexist adjacent to the 80 K phase at relatively low temperatures such as 400 °C.