The oxyfluoride superconductor, Sr2CuO2F2+δ, was prepared by a sol-gel method. Two different routes were examined; one was an attempt to prepare the Sr2CuO2F2+δ phase directly from fluorine-containing sols, and the other was the fluorination of sol-gel-derived Sr2CuO3 fine powders by F2 gas. The former route did not lead to the formation of oxyfluorides because of the precipitation of SrF2 by the heat treatments of the gel. The latter route led to the formation of the Sr2CuO2F2+δ phase. The amount of the Sr2CuO2F2+δ phase and superconducting properties of the powders depended on the fluorinating condition such as F2 gas concentration and fluorinating time. The Tc values reached 45-47 K by annealing the fluorinated samples in vacuo. The magnetization hysteresis loop was measured for the first time in the oxyfluoride superconductors.
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