Influence of radiation-induced disordering on the superconducting transition temperature ofNb3Ir films

Evaporated single-phase A15 ${\mathrm{Nb}}_3$Ir films were irradiated at room temperature with protons and helium ions to study the influence of the induced defect structures determined by x-ray diffraction measurements on the superconducting transition temperature $T_c$. A reduction in $T_c$ from 2.1 to 1.8 K was observed for energies deposited into nuclear collisions below 1 eV/atom. Beyond this threshold $T_c$ increased and revealed values above the initial transition temperature of the unirradiated films depending on the irradiation conditions: 2.8 K for proton and 3.7 K for helium-ion irradiation. The changes in $T_c$ were accompanied by a decrease of the Bragg-Williams long-range order parameter, a defect structure consisting of static displacements of the lattice atoms with average rms amplitudes in the range of 0.005 to 0.009 nm, and by partial amorphization. The maximum $T_c$ value of 5.7 K was determined in totally amorphized films. Both the depressions and enhancements in $T_c$ can be explained by changes of the electronic density of states at the Fermi energy due to smearing effects.