Influence of fast neutron irradiation on inter- and intragrain properties of ceramic YBa/sub 2/Cu/sub 3/O/sub 7/

Fast neutron irradiation of YBa/sub 2/Cu/sub 3/O/sub 7/ leads to a decrease of T/sub c/, the variation of the ratio T/sub c/( Phi t)/T/sub c/(O) being comparable to that observed in conventional superconducting compounds. Superconductivity vanishes above a fluence of 2*10/sup 19/ cm/sup 2/. The phase-locking temperature of the intergrain junctions decreases faster with fluence than T/sub 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/sub cG/ increases with increasing fluence, but its dependence on B and Phi t is not at all in accordance with increasing pinning by radiation-induced defects and decreasing T/sub c/. The intragrain current drops remarkably at low fields, passing a minimum and a subsequent maximum beyond which the common decrease of j/sub cG/ with increasing field is observed. The low-field behavior, together with the much lower increase of j/sub cG/ with fluence than above the maximum, points to a junction character of the current in this field range.<
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