Evidence for Irradiation Triggered Nonuniform Defect Distribution In   Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa2Cu3O7-x
  Multiharmonic ac-magnetic susceptibility \ch11,\chi2,chi3, of neutron irradiated Li-doped YBa2Cu3O7-x has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at aneutron fluence of 0.98x10$^{17}$ cm$_{-2}$. Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence \Phi = 9.98x10$^{17}$ cm$_{-2}$. We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect rich regions. 
V. Sandu, S. Popa, D. Di Gioacchino, P. Tripodi