⁵⁷Fe mössbauer spectroscopy of U₆Fe

Samples of U₆Fe were prepared by arc melting uranium and enriched ⁵⁷Fe. The samples display superconducting transitions which are sensitive to longterm exposure to air. Room temperature spectra of U₆Fe typically display a majority site A (quadrupole splitting Δ = 0.749(3)mm s^-1, isomer shift δ = - 0.482(6)mm s^-1 relative to copper and a minority site B (Δ = 0.55(3) mm s^-1, δ = -0.12(3)mms^-1 with the site intensity ratio I_B I_A typically 0.05 to 0.10. The I_B I_A intensity ratio increases upon air exposure of the samples. We have studied Mössbauer spectra as a function of temperature Tin the range 15K≤ T ≤ 310K, paying particular attention to the T variation of the isomer shift and recoil-free fraction of the majority site A. The results indicate a softening of lattice vibrations of U₆Fe at T ≲ 170 K.