The rhenium carbide Re3C was predicted to be stable under high pressure and expected to have high hardness and low compressibility. In this study, we realise the synthesis of Re3C at megabar pressures of 105(3) and 140(5) GPa in laser-heated diamond anvil cells and characterise its structure using synchrotron single-crystal X-ray diffraction. The structure of Re3C has the monoclinic space group C2/m and is built of CRe7 capped octahedra. Our combined ab initio calculations and quantitative topological analysis support experimental structural data and further deepen the understanding of the chemical bonding in the newly synthesized compound.

Single-crystal Brillouin scattering measurements are important for interpreting seismic velocities within the Earth and other planetary interiors. These measurements are rare, however, at temperatures above 1000 K, due to the fact that the transparent samples cannot be heated by common laser heating systems operating at a wavelength on the order of 1 μm. Here we present Brillouin scattering data on pyrope collected at pressures up to 23.8 GPa and temperatures between 850 and 1900 K using a novel CO2 laser heating system confined in either a flexible hollow silica waveguide or an articulated arm with mirrors mounted in each junction to direct the laser to the exit point. Pyrope has been chosen because it has been extensively studied at high pressures and moderate temperatures and therefore it is an excellent sample for bench-marking the CO2 laser heating system. The new high-temperature velocity data collected in this study allow the room pressure thermal parameters of pyrope to be constrained more tightly, resulting in values that reproduce the temperature dependence of the unit-cell volume of pyrope measured in recent studies at ambient pressure. Aggregate wave velocities of pyrope calculated along an adiabat using the thermoelastic parameters determined in this study are larger than those obtained using published values, implying that velocities for many mantle components may be underestimated at mantle temperatures because high temperature experimental data are lacking.

Scandium (Sc) is a rare element that finds uses in modern technologies. Thermodynamic properties of Sc phases could help in the development of innovative technologies to extract Sc from mining waste. In this work, we investigated the FeOOH–ScOOH solid solution with the goethite structure. The end members and five intermediate compositions were synthesized and characterized. The lattice parameters show that the solid solution is non-ideal, with complex behavior induced by the Fe–Sc substitution. The excess unit-cell volume deviates negatively for the Sc-rich region, and positively for the Fe-rich region from the ideal behavior (Vegard’s law). Enthalpies of dissolution were determined by acid-solution calorimetry in 5 mol·dm-3 HCl at T = 343.15 K. Enthalpies of mixing (ΔmixH), calculated from the experimental data, are small and positive. The available data allow for fitting the data as ΔmixH=Wx(1-x), with the mixing parameter W=15.2±1.0 kJ·mol-1. Using ΔfGo of ScOOH from earlier literature, we calculated a Lippmann diagram that shows that Sc should strongly partition into the aqueous phase upon goethite precipitation. The field observations from lateritic profiles show that Sc is primarily harbored by goethite via adsorption. It seems that under weathering conditions, thermodynamically driven partitioning of Sc3+ into the aqueous phases and its subsequent adsorption onto goethite surfaces controls the mobility of Sc in the weathering profiles.

Studying the anisotropic physical properties of hexagonal closed-packed (hcp) iron is essential for understanding the properties of the Earth’s inner core related to the preferred orientation of the inner core materials suggested by seismic observations. Investigating the anisotropic physical properties of hcp iron requires (1) the synthesis of hcp iron samples that exhibit several distinctive types of strong lattice preferred orientation (LPO) and (2) the quantitative LPO analysis of the samples. Here, we report the distinctive LPO of hcp iron produced from single-crystal body-centered cubic (bcc) iron compressed along three different crystallographic orientations ([100], [110], and [111]) in a diamond anvil cell based on synchrotron multiangle X-ray diffraction measurements up to 80 GPa and 300 K. The orientation relationships between hcp iron and bcc iron are consistent with the Burgers orientation relationship with variant selection. We show that the present method is a way to synthesize hcp iron with strong and characteristic LPO, which is beneficial for experimentally evaluating the anisotropic physical properties of hcp iron.