Improvement of the superconducting properties of YBa2Cu3O 7-x by thermal treatment

Abstract
Superconducting properties of the high Tc superconductor YBa2Cu3O7-x were optimized through a systematic study of the influence of the last thermal treatment of sintered pellets in open air. A.c. susceptibility measurements used to test the superconducting behaviour show sharp transitions, about 2 K wide, with onset temperatures near 91 K, when annealing is performed in a very narrow temperature range, near 440 °C, for a few hours. The samples obtained are very homogeneous, with an oxygen content close to 7. Higher annealing temperatures lead to lower Tc and transition broadening. Moreover, slow cooling appears to be unnecessary. The described thermal treatment, very easy in application and completely reversible, also applies to other REBa2Cu 3O7-x materials (RE = rare earth)