Development of Space Instabilities of Defect Distribution at High Fluences in Neutron Irradiated YBa2Cu3O7−δ Ceramics

We investigated the behaviour of YBa2Cu2O7-{delta} ceramics by multiharmonic ac-susceptibility. We have found an unexpected improvement of the intragranular response at the highest fluence 9.98 1017 neutrons/cm2. However, this fact is accompanied with a continuous suppression of the intergranular properties. We assume that this behavior is the result of the change of the nature of defect distribution at high fluence, when the uniform distribution of defects starts to develop space instabilities as a result of the subtle interplay of the in-cascade rate of interstitial loops production, cascade collapse of the vacancy loops, and the excess network bias.