Study of microstructural changes in MgB2 thin film superconductors irradiated with 200 MeV 107Ag ions

Abstract

MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evaporation (EBE), have been investigated by scanning electron microscopy (SEM) before and after 200 MeV 107Ag ion irradiation. The severe degradation of superconducting properties in irradiated PLD film and the absence of the same in EBE film correlates with the observed changes in their microstructures. The micrographs of the PLD film show an overall smoothing, flow pattern and reduction in size of the bigger agglomerates after irradiation. On the other hand, the microstructure of the EBE film does not show any significant change after irradiation. The flow pattern observed in the PLD film can be understood on the basis of the viscoelastic model for irradiation induced shear flow in amorphous solids. The observed degradation of the PLD film may thus be attributed primarily to its disordered nature under irradiation, whereas the radiation hardness of the EBE film may be due to its higher crystallinity.