The critical current density ${\mathit{J}}_{\mathit{c}}$ in ${\mathrm{Y}}_{0.9}$${\mathrm{Gd}}_{0.1}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ was found to increase relative to the unirradiated value following neutron irradiations in a mixed-spectrum reactor (total neutron fluences ranged between 1×${10}^{17}$ and 2×${10}^{18}$ n/${\mathrm{cm}}^2$). Additional neutron irradiations of structurally similar ${\mathrm{GdBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ were carried out in either a highly thermalized or a pure fast-neutron environment (in the same reactor). This was done to determine whether enhancements in ${\mathit{J}}_{\mathit{c}}$ are to be attributed to defects arising from interactions with thermal neutrons (${\mathit{E}}_{\mathit{n}}$∼0.025 eV) or with fast neutrons (${\mathit{E}}_{\mathit{n}}$>0.1 MeV). Magnetic-hysteresis measurements on these samples indicate that flux pinning (and thereby ${\mathit{J}}_{\mathit{c}}$) is enhanced by fast-neutron irradition, but not by thermal-neutron irradiation. On the other hand, the critical temperature ${\mathit{T}}_{\mathit{c}}$ is significantly altered by exposure both to thermal and fast neutrons. It is proposed that thermal neutrons induce the formation of Frenkel pair defects on the rare-earth sublattice, but that these point defects do not serve as effective flux-pinning centers.

• Received 30 March 1992

DOI:https://doi.org/10.1103/PhysRevB.46.11862