Wolfgang Sturhahn, Advanced Photon Source, Argonne National Laboratory
In recent years, nuclear resonant scattering techniques that utilize synchrotron radiation have provided new opportunities for the study of vibrational properties, magnetic properties, and iron valancies of condensed matter under extreme conditions. Here we discuss nuclear resonant inelastic x-ray scattering (NRIXS), a method that uses probe nuclei with suitable resonances to measure the vibrational density of states, and synchrotron Moessbauer spectroscopy (SMS) for determination of valancies. Both methods are very sensitive to small amounts of material and take advantage of the high brilliance of synchrotron radiation, which makes micrometer-sized x-ray beams with high intensity possible. These properties allowed NRIXS and SMS investigations on materials under pressures in the Mbar regime using diamond anvil cells [1,2]. We will present data on iron, iron-rich alloys, and iron-containing perovskites (Fe,Mg)SiO3 to exemplify the usefulness of these novel techniques for the geophysical problem area. The experimental methods and the interpretation of the data will be elucidated with particular emphasis on phonon density of states extraction [3], sound velocity determination [4], and the abundance of ferric iron in lower mantle minerals. Possibilities of NRIXS and SMS measurements under high pressure and high temperature conditions are presented and future developments at beamlines of the Advanced Photon Source will be discussed.
This work is supported by the U.S. DOE-BES, Office of Science, under Contract No. W-31-109-Eng-38.
[1] H.K.Mao, J.Xu, V.V.Struzhkin, J.Shu, R.J.Hemley, W.Sturhahn, M.Y.Hu, E.E.Alp,
L.Vocadlo, D.Alfe, G.D.Price, M.J.Gillan, M.Schwoerer-Boehning, D.Haeusermann,
P.Eng, G.Shen, H.Giefers, R.Luebbers, G.Wortmann, Science 292, 914 (2001)
[2] J.M.Jackson, W.Sturhahn, G.Shen, J.D.Bass, (unpublished)
[3] W.Sturhahn, T.S.Toellner, E.E.Alp, X.Zhang, M.Ando, Y.Yoda, S.Kikuta, M.Seto, C.W.Kimball, and B.Dabrowski, Phys.Rev.Lett. 79, 3832 (1995)
[4] M.Y.Hu, W.Sturhahn, T.S.Toellner, P.Mannheim, E.E.Alp, Phys.Rev. B 67, 094304 (2003)