Bi-Pb-Sr-Ca-Cu-O系高温相の化学的および機械的安定性(II) : Tcのアニール雰囲気による変化

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Effect of annealing atmosphere and temperature on the superconducting properties Tc have been discussed in the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system. Special attention has been given to oxygen sorption/desorption and formation of impurity phases. The bulk samples without presence of amorphous phase formed due to mechanical grinding were used for compositions of Bi0.9Pb0.2Sr1.0BaxCa1.0Cu1.6Oz (x=0 and 0.05). Annealing in O2 and air above 700°C leads to marked weight increase and formation of (Bi, Pb)3Sr2Ca2CuOz. In contrast, almost monophasic samples of the high-Tc phase, absent from any impurity phases, were obtained on annealing in Ar. Furthermore, the weight of samples with x=0 and 0.05 decreses by Ar-annealing at temperatures of 350°C and 800-830°C. The weight decrease due to oxygen-desorption results in an elongation of the c-axis length of the high-Tc phase, accompanying an increase in Tc.