Y-Ba-Cu-O-F系超伝導体の作製と評価

概要

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Fluorine (F) substitution effects on the superconducting properties are investigated with YBa_2Cu_3O_xF_y prepared by two different methods. At first, the sintered samples were prepared with the appropriate mixture of Y_2O_3, Ba_2O_3, CuO and several fluorides. Since the samples had strong peaks of BaF_2 phase together with the perovskite one in the X-ray diffraction patterns, it was difficult to obtain information on the F-substitution effects on the physical properties. Next, the samples were prepared by annealing YBa_2Cu_3O_x sintered pellets and CoF_3 powder in a sealed quartz tube. In this case, the crystalline state was a single phase of the orthorhombic perovskite structure. It was found that the diamagnetic susceptibility X decreased concurrently to the increase of the F content and the temperature dependence of X was similar regardless of the presence of F-substitution. This indicates that the volume fraction of the superconductor phase decreased. In the resistivity measurement, the superconductivity was not observed down to 4.2 K. These results suggests that the F atoms enter the crystalline grains from the surfaces and change the superconductivity state into a normal one in the vicinity of the crystalline grain surfaces.
社団法人日本セラミックス協会の論文
1988-04-01