Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from their extraction to the core during terrestrial accretion. Experiments to investigate the partitioning of these elements between metal and silicate melts suggest that the PUM composition is best matched if metal-silicate equilibrium occurred at high pressures and temperatures, in a deep magma ocean environment. The behavior of the most highly siderophile elements (HSEs) during this process however, has remained enigmatic. Silicate run-products from HSE solubility experiments are commonly contaminated by dispersed metal inclusions that hinder the measurement of element concentrations in the melt. The resulting uncertainty over the true solubility and metal-silicate partitioning of these elements has made it difficult to predict their expected depletion in PUM. Recently, several studies have employed changes to the experimental design used for high pressure and temperature solubility experiments in order to suppress the formation of metal inclusions. The addition of Au (Re, Os, Ir, Ru experiments) or elemental Si (Pt experiments) to the sample acts to alter either the geometry or rate of sample reduction respectively, in order to avoid transient metal oversaturation of the silicate melt. This contribution outlines procedures for using the pistoncylinder and multi-anvil apparatus to conduct solubility and metal-silicate partitioning experiments respectively. A protocol is also described for the synthesis of uncontaminated run-products from HSE solubility experiments in which the oxygen fugacity is similar to that during terrestrial core-formation. Time-resolved LA-ICP-MS spectra are presented as evidence for the absence of metal-inclusions in run-products from earlier studies, and also confirm that the technique may be extended to investigate Ru. Examples are also given of how these data may be applied.

Icosahedrite, the first natural quasicrystal with composition Al63Cu24Fe13, was discovered in several grains of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The presence of icosahedrite associated with high-pressure phases like ahrensite and stishovite indicates formation at high pressures and temperatures due to an impact-induced shock. Previous experimental studies on the stability of synthetic icosahedral AlCuFe have either been limited to ambient pressure, for which they indicate incongruent melting at similar to 1123 K, or limited to room-temperature, for which they indicate structural stability up to about 35 GPa. These data are insufficient to experimentally constrain the formation and stability of icosahedrite under the conditions of high pressure and temperature that formed the Khatyrka meteorite. Here we present the results of room-temperature, high-pressure diamond-anvil cells measurements of the compressional behavior of synthetic icosahedrite up to 50 GPa. High P-T experiments were also carried out using both laser-heated diamond-anvil cells combined with in situ synchrotron X-ray diffraction (at 42 GPa) and multi-anvil apparatus (at 21 GPa) to investigate the structural evolution and crystallization of possible coexisting phases. The results demonstrate that the quasiperiodic order of icosahedrite is retained over the P-T range explored. We find that pressure acts to stabilize the icosahedral symmetry at temperatures much higher than previously reported. Direct solidification of AlCuFe quasicrystals from an unusual Al-Cu-rich melt is possible but it is limited to a narrow temperature range. Alternatively, quasicrystals may form after crystallization through solid-solid reactions of Al-rich phases. In either case, our results show that quasicrystals can preserve their structure even after hypervelocity impacts spanning a broad range of pressures and temperatures.

Compressed hydrogen passes through a series of layered structures in which the layers can be viewed as distorted graphene sheets. The electronic structures of these layered structures can be understood by studying simple model systems-an ideal single hydrogen graphene sheet and three-dimensional model lattices consisting of such sheets. The energetically stable structures result from structural distortions of model graphene-based systems due to electronic instabilities towards Peierls or other distortions associated with the opening of a band gap. Two factors play crucial roles in the metallization of compressed hydrogen: (i) crossing of conduction and valence bands in hexagonal or graphenelike layers due to topology and (ii) formation of bonding states with 2p(z)pi character.

We report a synthetic route to mesoporous crystalline aluminosilica materials using high pressure and temperature. In the first step a large-pore periodic mesoporous aluminosilica SBA-15 material was filled with carbon at ambient pressure. We observed that crystallization of the pore walls of periodic mesoporous aluminosilica/carbon composites occurred at 2 GPa and a temperature of 650 degrees C without significant distortion of the mesostructure. Combustive removal of carbon from the crystallized composite in air led to the formation of periodic mesoporous crystalline aluminosilica materials. These materials are steam stable and are resistant to shrinkage under the harsh conditions of hydrothermal treatment at 800 degrees C.

Theoretical calculations and an assessment of recent experimental results for dense solid hydrogen lead to a unique scenario for the metallization of hydrogen under pressure. The existence of layered structures based on graphene sheets gives rise to an electronic structure related to unique features found in graphene that are well studied in the carbon phase. The honeycombed layered structure for hydrogen at high density, first predicted in molecular calculations, produces a complex optical response. The metallization of hydrogen is very different from that originally proposed via a phase transition to a close-packed monoatomic structure, and different from simple metallization recently used to interpret recent experimental data. These different mechanisms for metallization have very different experimental signatures. We show that the shift of the main visible absorption edge does not constrain the point of band gap closure, in contrast with recent claims. This conclusion is confirmed by measured optical spectra, including spectra obtained to low photon energies in the infrared region for phases III and IV of hydrogen.

BaReH9 is an exceedingly high-hydrogen-content metal hydride that is predicted to exhibit interesting behavior under pressure. The high-pressure electronic properties of this material were investigated using diamond-anvil-cell electrical conductivity techniques to megabar (100 GPa) pressures. The measurements show that BeReH9 transforms into a metal and then a superconductor above 100 GPa with a maximum transition temperature (T-c) near 7 K. The occurrence of superconductivity was confirmed by the suppression of the resistance drop upon application of magnetic fields. The transition to the metallic phase is sluggish, but it is accelerated by laser irradiation. Raman scattering and X-ray diffraction measurements, used to supplement the electrical measurements, indicate that the Ba-Re sublattice is largely preserved upon compression under the conditions explored, but there is a possibility that hydrogen atoms are gradually disordered under pressure. This is suggested by the sharpening of the peaks in Raman spectroscopy and X-ray diffraction upon heat treatment, as well as the temperature dependence of the resistance under pressure. The data suggest that the transition to the superconducting state is first-order. The possibility that the transition is associated with the breakdown of BeReH9 is discussed.

Fe-S-P compounds have been observed in many meteorites and could be the important components in planetary cores. Here we investigated the phase stability of Fe-3(S,P) solid solutions and synthesized high-quality Fe3(Si_ 13x) high-pressure phases in the multi-anvil press. The physical properties of Fe-3(S0.5130.5) were further studied in the diamond-anvil cell by synchrotron X-ray diffraction and emission spectroscopy. The solubility of S in the Fe-3(S,P) solid solution increases with increasing pressure. The minimum pressure to synthesize the pure Fe3S and Fe-3(S0.13P0.87) is about 21 and 8 GPa, respectively. The observed discontinuity in unit-cell parameters at about 18 GPa is caused by the high-spin to low spin transition of iron, supported by X-ray emission spectroscopy data. The sulfur solubility in Fe-3(S,P) solid solutions could be an excellent pressure indicator if such solid solutions are found in nature.

Raman spectroscopy of dense hydrogen and deuterium performed to 325 GPa at 300 K reveals previously unidentified transitions. Detailed analysis of the spectra from multiple experimental runs, together with comparison with previous infrared and Raman measurements, provides information on structural modifications of hydrogen as a function of density through the I-III-IV transition sequence, beginning near 200 GPa at 300 K. The data suggest that the transition sequence at these temperatures proceeds by formation of disordered stacking of molecular and distorted layers. Weaker spectral changes are observed at 250, 285, and 300 GPa, that are characterized by discontinuities in pressure shifts of Raman frequencies, and changes in intensities and linewidths. The results indicate changes in structure and bonding, molecular orientational order, and electronic structure of dense hydrogen at these conditions. The data suggest the existence of new phases, either variations of phase IV, or altogether new structures.

The discovery of diamonds and highly reduced minerals in podiform chromitites, which have generally been interpreted as magmatic rocks formed from partial melts of upper mantle peridotites under low-pressure conditions, has raised many questions about the origin of these enigmatic bodies. In order to provide experimental constraints on the formation and emplacement of podiform chromititesin ophiolites, we carried out a number of multi-anvil experiments in the magnesiochromite + SiO2 system at temperatures of 1000-1600 degrees C and pressures of 5-15 GPa. The experimental results demonstrate that magnesiochromite is stable up to 14 GPa and decomposed into eskolaite (Cr2O3) together with a quenchable modified ludwigite-structured phase [(Fe, Mg)(2)(Al, Cr)(2)O-5] at higher pressures, thus placing an approximate maximum depth for chromite crystallization and/or metamorphism. This depth corresponds to the top of the mantle transition zone (MTZ) at 410 km. The ludwigite-structured post-chromite phase has significant implications for understanding phase transformations and Cr incorporation/partitioning of minerals in the MTZ. On the basis of our results, we propose a multi-stage model for the formation of podiform chromitites that incorporates the geochemical, textural and mineralogical features of these bodies. (C) 2015 Elsevier B.V. All rights reserved.