Neutron-irradiated superconducting YBa2Cu3(Li)O7-δ with improved irreversibility

Irradiation of YBa 2 Cu 3 (Li)O 7-δ ceramics with thermal and epithermal neutrons at fluences higher than 10 17 neutrons/cm 2 has led to a spectacular improvement of the intragranular properties. The critical current density has shown a monotonous dependence. The suppression of the critical temperature was below 2% but shows an increase at 9.8x10 17 neutrons/cm 2 . This behaviour is consistent with the appearance of self-organized population of defects at high fluence. An analysis of the nature of the defect distribution, which is responsible for these effects, is provided.