Investigations on the valence state of Fe diluted in Cu by spectroscopy of the K x-ray energy shifts

We report here first results on the electronic structure of Fe dissolved in Cu with a concentration of 370 ppm which have been obtained by applying X-ray emission spectroscopy following K-shell ionization by electrons of 100 keV impact energy. Annealed and unannealed samples of CuFe were investigated by detecting the Fe Kα1 and Kα2 X-rays with a flat crystal spectrometer using a LiF(200) crystal in 2nd order. We obtain for the annealed sample in line shift — with respect to a pure Fe sample — of (0.026±0.113) eV for the Kα1 transition and (-0.046±0.176) eV for the Kα2 transition and accordingly for the unannealed sample (0.012±0.086) and (-0.224±0.167) eV. For the difference between the two transition energies, i.e. ΔE = E(Kα1)−E(Kα2), we deduce ΔE = (13.07±0.22) eV for the annealed sample and (13.27±0.16) eV for the unannealed one. A comparison of the measured Kα X-ray energies with Dirac-Fock calculations of the energy states for free Fe ions does not yield an unambigous answer on the ionic state of Fe in the annealed CuFe sample. In the unannealed sample the measured X-ray energies have values that lie between the calculation for an Fe2+ and Fe3+ ion. The consequences of these findings with respect to the magnetic properties of Fe are discussed.