Sound velocities of compressed Fe₃C from simultaneous synchrotron X-ray diffraction and nuclear resonant scattering measurements

Abstract

The applications of nuclear resonant scattering in laser-heated diamond anvil cells have provided an important probe for the magnetic and vibrational properties of (57)Fe-bearing materials under high pressure and high temperature. Synchrotron X-ray diffraction is one of the most powerful tools for studying phase stability and equation of state over a wide range of pressure and temperature conditions. Recently an experimental capability has been developed for simultaneous nuclear resonant scattering and X-ray diffraction measurements using synchrotron radiation. Here the application of this method to determine the sound velocities of compressed Fe(3)C is shown. The X-ray diffraction measurements allow detection of microscale impurities, phase transitions and chemical reactions upon compression or heating. They also provide information on sample pressure, grain size distribution and unit cell volume. By combining the Debye velocity extracted from the nuclear resonant inelastic X-ray scattering measurements and the structure, density and elasticity data from the X-ray diffraction measurements simultaneously obtained, more accurate sound velocity data can be derived. Our results on few-crystal and powder samples indicate strong anisotropy in the sound velocities of Fe(3)C under ambient conditions.

Iron Carbide Inclusions in Lower-Mantle Diamond From Juina, Brazil

“…These conclusions can be applied to the inner core as well, where the density deficit is lower but still significant (~2.5-9%). Iron carbide in the inner core would explain both the observed seismic anisotropy and the density of the inner core, which is lower than pure iron under corresponding pressure and temperature conditions (Gao et al, 2009). According to the data on sound velocity for iron carbide at high pressures, a reduced carbon content in the inner core (corresponding to ~1 wt.% of carbon) could reasonably explain density and velocity differences between measurements made on pure iron and the seismic models (Fiquet et al, 2009).…”

Nuclear resonant inelastic X-ray scattering at high pressure and low temperature

“…With the X-ray beam incident at grazing incidence angle, sample thickness has been reduced to a monolayer Stankov et al, 2010). In an attempt to combine several environmental parameters, high pressure and high temperature have been achieved using laser heating in diamond anvil cells (DACs) (Zhao et al, 2004;Lin et al, 2005;Gao et al, 2009;Jackson et al, 2013). With a renewed interest in phonon physics due to the discovery of novel superconductivity in iron pnictides and chalcogenides (Boeri et al, 2008;Hahn et al, 2009;Sergueev et al, 2013;Kobayashi et al, 2013), it has become imperative to carry out NRIXS experiments under high-pressure (HP) and low-temperature (LT) conditions.…”

“…The setup described here accommodates two APDs which are placed around the sample in a plane perpendicular to the incoming X-ray beam. An online X-ray diffraction system with a MAR3450 image plate detector is used to collect diffraction spectra from the sample or the pressure marker in order to determine the lattice parameters of the sample or to determine the pressure in the sample chamber (Gao et al, 2009). An online ruby fluorescence system is available for in situ pressure measurements.…”

High-pressure studies with x-rays using diamond anvil cells

“…From the low-energy region of each phonon DOS, Debye sound velocity can be derived. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Phonon DOS has been determined for a number of iron compounds and alloys: FeO [519,520], FeS [521], Fe-Ni [522], Fe-Si alloys [287,522], FeH [523], Fe3S [524], Fe3C [525][526][527], Fe2O3 [528], (Mg,Fe)O [497], and (Mg,Fe)SiO3 enstatite [529]. For nanocrystalline Fe, large distortions were found in its phonon DOS [530], showing a lifetime broadening at high energies and an enhancement in its phonon DOS at energies below 15 meV.…”

“…Examples of sound velocity determination using NRIXS include: Fe [63,297,517,518], FeO [519,520], FeS [521], Fe-Ni [522], Fe-Si alloys [287,522], FeH [523], Fe3S [524], Fe3C [525][526][527], Fe2O3 [528], and (Mg,Fe)O [497]. The Debye parabola is best constrained at the low-energy limit, and a resolution of better than 2 meV is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 therefore essential in NRIXS for approaching that limit.…”