Superstructure of tetrataenite from the Saint Severin meteorite

Abstract

Abstract The superstructure of tetrataenite, FeNi from the Saint Severin meteorite was determined using X-ray diffraction data from a conventional X-ray source and synchrotron radiation. Lattice constants of tetrataenite show clearly tetragonal symmetry; a = 3.581(2) Å, b = 3.582(2) Å, c = 3.587(2) Å, α = 90.03(3)°, β = 90.04(3)° and γ = 90.00(3)°. The structure, however, is monoclinic. The space group may be Pm. The atomic coordinates and the temperature were determined by data from conventional X-ray diffraction. The ordering of Fe/Ni was determined by refinement of site occupancies of the atoms applying the difference of anomalous scattering factors of Fe and Ni with synchrotron radiation λ = 1.746 Å. The tetrataenite from the Saint Severin meteorite does not show perfect ordering of Fe and Ni. It still contains 15% disorder of Fe/Ni on average.