The effect of Fe in Fe-doped YBa2Cu3O7 superconductors

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Abstract
A series of samples of YBa2(Cu1−xFex)3O7 with x ranging from 0 to 0.13 was made and investigated by x‐ray diffraction, dc SQUID magnetometry, and Mössbauer spectroscopy. In the samples made by the ordinary process, Fe mainly occupies Cu(1) sites. The orthorhombic‐to‐tetragonal structural transition occurs at x≂0.03, and the superconducting transition temperature is depressed to zero at x≂0.17. By annealing the samples in Ar gas at 750 °C for 24 h and then reloading the lost oxygen in O2 gas at 210 °C for 48 h, we were able to draw about 30% of the Fe from Cu(1) sites into Cu(2) sites. This was verified by the enhancement of the component in the Mössbauer spectrum corresponding to Fe in the Cu(2) sites. The structural and superconducting properties of this new series of samples were also investigated. Comparison with the ordinary Fe‐doped samples was also made.