Ferric iron in Al-bearing post-perovskite

The Fe3+/∑Fe ratios in both (Al, Fe)-bearing MgSiO3 post-perovskite phase and Ca-ferrite-type Al-phase, synthesized in a natural mid-oceanic ridge basalt (MORB) composition at 113 GPa and 2240 K, were determined by electron energy-loss near-edge struct

The influence of solid solution on elastic wave velocity determination in (Mg,Fe)O using nuclear inelastic scattering

Elastic wave velocities of minerals are important for constraining the chemistry, structure and dynamics of the Earth’s mantle based on the comparison between laboratory-based measurements and seismic observations. As the second most abundant phase in the Earth’s lower mantle, (Mg,Fe)O ferropericlase has been the focus of numerous studies measuring the elastic wave velocities using various methods such as Brillouin spectroscopy and ultrasonic measurements. Recently, nuclear inelastic scattering (NIS) has been used to determine elastic wave velocities of iron-bearing phases. However, the elastic wave velocities of ferropericlase obtained using NIS are considerably lower than the velocities obtained by other methods, even at ambient conditions. One possible source of this discrepancy is the local nature of the NIS method. In order to test this hypothesis, we have investigated six ferropericlase samples with various iron contents using NIS. The Debye sound velocities calculated using the conventional method of NIS analysis are consistent with previous results obtained using NIS, yet the values are significantly lower than those obtained using ultrasonics and Brillouin spectroscopy. If the Debye sound velocities are re-calculated based on a mixture of different iron next-neighbour configurations with different compositions, the Debye sound velocities determined by NIS agree well with the results from other methods. Our new model was also successfully applied to high-pressure NIS data taken from the literature. Our results constitute an important step towards a better understanding of how to obtain reliable sound velocities of iron-bearing mantle minerals from NIS measurements

Critical behavior of Mg1–xFexO\mathrm{Mg_{1–x}Fe_{x}O} at the pressure-induced iron spin-state crossover

We present a high-pressure study of Mg$_{1–x}$Fe$_{x}$O (ferropericlase, Fp) single crystals 0.04(1)$\leqslant x \leqslant$ 0.33(1) with a focus on ferrous iron spin-state crossover and the material behavior preceding it. Using Vegard's law and highly accurate high-pressure single-crystal experimental data, we extract the lattice parameter $a^{HS}_{FeO}$ of the “FeO high spin lattice contribution” in the MgO-FeO solid solution. We find that ferropericlases with a wide range of compositions share the same critical parameter $a_C$ (defined as the minimum $a^{HS}_{FeO}$ after which spin crossover starts). Furthermore, we discuss the effect of composition on spin crossover in ferrous iron in ferropericlase in the limits of low and moderate concentrations of Fe$^{2+}$

Sound velocities of skiagite–iron–majorite solid solution to 56 GPa probed by nuclear inelastic scattering

High-pressure experimental data on sound velocities of garnets are used for interpretation of seismological data related to the Earth’s upper mantle and the mantle transition zone. We have carried out a Nuclear Inelastic Scattering study of iron-silicate garnet with skiagite (77 mol%)–iron–majorite composition in a diamond anvil cell up to 56 GPa at room temperature. The determined sound velocities are considerably lower than sound velocities of a number of silicate garnet end-members, such as grossular, pyrope, Mg–majorite, andradite, and almandine. The obtained sound velocities have the following pressure dependencies: $V_p$ [km/s] = 7.43(9) + 0.039(4) × P [GPa] and $V_s$ [km/s] = 3.56(12) + 0.012(6) × P [GPa]. We estimated sound velocities of pure skiagite and khoharite, and conclude that the presence of the iron–majorite component in skiagite strongly decreases $V_s$ . We analysed the influence of Fe$^{3+}$ on sound velocities of garnet solid solution relevant to the mantle transition zone and consider that it may reduce sound velocities up to 1% relative to compositions with only Fe$^{2+}$ in the cubic site

Portable double-sided laser-heating system for Mössbauer spectroscopy and X-ray diffraction experiments at synchrotron facilities with diamond anvil cells

The diamond anvil cell (DAC) technique coupled with laser heating is a major method for studying materials statically at multimegabar pressures and at high temperatures. Recent progress in experimental techniques, especially in high-pressure single crystal X-ray diffraction, requires portable laser heating systems which are able to heat and move the DAC during data collection. We have developed a double-sided laser heating system for DACs which can be mounted within a rather small ( 3c0.1 m2) area and has a weight of 3c12 kg. The system is easily transferable between different in-house or synchrotron facilities and can be assembled and set up within a few hours. The system was successfully tested at the High Pressure Station of White Beam (ID09a) and Nuclear Resonance (ID18) beamlines of the European Synchrotron Radiation Facility. We demonstrate examples of application of the system to a single crystal X-ray diffraction investigation of (Mg0.87,Fe 3+0.09,Fe2+0.04)(Si 0.89,Al0.11)O3 perovskite (ID09a) and a Synchrotron M\uf6ssbauer Source (SMS) study of (Mg0.8Fe 0.2)O ferropericlase (ID18)