Influence of fast neutron irradiation on inter- and intragrain properties of ceramic YBa2Cu3O7

Fast neutron irradiation of YBa₂Cu₃O₇ leads to a decrease of T_c, the variation of the ratio T_c(Φt)/T_c(O) being comparable to that observed in conventional superconducting compounds. Superconductivity vanishes above a fluence of 2×10¹⁹ cm ². The phase-locking temperature of the intergrain junctions decreases faster with fluence than T_c. Lower AC losses due to a complete destruction of weak links and lower intergrain critical-current densities with increasing fluence reflect in addition a larger radiation sensitivity of the intergrain junction properties. The intragrain critical-current density j_cG increases with increasing fluence, but its dependence on B and Φt is not at all in accordance with increasing pinning by radiation-induced defects and decreasing T_c. The intragrain current drops remarkably at low fields, passing a minimum and a subsequent maximum beyond which the common decrease of j_cG with increasing field is observed. The low-field behavior, together with the much lower increase of j_cG with fluence than above the maximum, points to a junction character of the current in this field range