Ion beam amorphization of YBa/sub 2/Cu/sub 3/O/sub x/

The microstructure of ion-implanted thin films of the superconductor YBa/sub 2/Cu/sub 3/O/sub x/ has been investigated by transmission electron microscopy. The superconducting properties of the films were dominated by large pancake-shaped grains of YBa/sub 2/Cu/sub 3/O/sub x/ with their c axis perpendicular to the substrate. Other grains of YBa/sub 2/Cu/sub 3/O/sub x/ whose c axis was parallel to the substrate formed spherulites. Irradiation with 500 keV O/sup +/ ions caused amorphous zones to appear on the grain boundaries between the pancake grains, which initially were free of amorphous or second phases. At higher dose a continuous amorphous layer 150 A thick was formed. However, the interior of the grains showed no irradiation-induced microstructural features until they became amorphous at a dose of 3 x 10/sup 14/ ions/cm/sup 2/. The appearance of the amorphous layer on the grain boundaries at low doses accounts for the reduction in the superconducting transition temperature observed in these films.