57Fe Mossbauer spectroscopy of U6Fe

Samples of U6Fe were prepared by arc melting U and enriched 57Fe. The samples display superconducting transitions which are sensitive to long-term exposure to air. Room temperature spectra of U6Fe typically display a majority site A (quadrupole splitting Δ = 0.749(3) mm/s, isomer shift delta = 0.482(6) mm/s relative to Cu) and a minority site B (Δ = 0.55(3) mm/s, sigma = 0.12(3) mm/s) with the site intensity ratio (I/sub B//I/sub A/) typically 0.05 to 0.10. The I/sub B//I/sub A/ intensity ratio increases upon air exposure of the samples. We have studied Moessbauer spectra as a function of temperature T in the range 150K less than or equal to T less than or equal to 3100K paying particular attention to the T-variation of the isomer-shift and recoil-free-fraction of the majority site A. Results indicate a consistent softening of lattice vibrations of U6Fe at T approx. = 1700K