Defect structure and superconducting transition temperature of ion-irradiated refractory metal carbides and nitrides

Abstract

Structural disorder and its influence on the superconducting transition temperature ( T c) of stoichiometric ZrN and HfN thin films irradiated with He ions (200 keV for ZrN and 400 keV for HfN) and Ar ions (600 keV for ZrN) have been investigated and compared to the results obtained for NbC films. With the preservation of the B1 phases, X-ray diffraction experiments have revealed lattice expansions at the first stage of ion irradiation ( Δa 0/ a 0 = 0.3% in ZrN and Δa 0/ a 0 = 0.2% in HfN) like for ion-irradiated NbC films, whereas subsequent lattice contractions are smaller in both nitride films. Static atomic displacements of metal atoms in ZrN films have shown a variation similar to that of the lattice parameter, but those in HfN films have increased continuously with irradiation fluence. T c's decreased continuously from 9.2 to 3.8K in ZrN and from 8.3 to 3.0K in HfN.