Our ability to interpret seismic observations including the seismic discontinuities and the density and velocity profiles in the earth's interior is critically dependent on the accuracy of pressure measurements up to 364 GPa at high temperature. Pressure scales based on the reduced shock-wave equations of state alone may predict pressure variations up to 7% in the megabar pressure range at room temperature and even higher percentage at high temperature, leading to large uncertainties in understanding the nature of the seismic discontinuities and chemical composition of the earth's interior. Here, we report compression data of gold (Au), platinum (Pt), the NaCl-B2 phase, and solid neon (Ne) at 300 K and high temperatures up to megabar pressures. Combined with existing experimental data, the compression data were used to establish internally consistent thermal equations of state of Au, Pt, NaCl-B2, and solid Ne. The internally consistent pressure scales provide a tractable, accurate baseline for comparing high pressuretemperature experimental data with theoretical calculations and the seismic observations, thereby advancing our understanding fundamental high-pressure phenomena and the chemistry and physics of the earth's interior.diamond-anvil cell ͉ high-pressure research ͉ pressure calibration ͉ thermodynamics ͉ x-ray diffraction T he earth has a layered internal structure with distinct boundaries. The boundaries of the five main layers (the upper mantle, the transition zone, the lower mantle, the liquid outer core, and the solid inner core) are well defined by the observed seismic velocity discontinuities at depths of 400, 670, 2,891, and 5,149 km (corresponding to pressures of 13.4, 23.8, 135.8, and 328.9 GPa, respectively) in a global average preliminary reference earth model (PREM) (1). The interpretation of these discontinuities requires experimental investigations of earth materials at high pressure and temperature. The seismic discontinuities near 400 and 670 km depth are commonly associated with the mineralogical phase transformations of (Mg,Fe) 2 SiO 4 from ␣-olivine to ␤-phase (wadsleyite) and from ␥-spinel (ringwoodite) to (Mg,Fe)SiO 3 -perovskite plus (Mg,Fe)O-magnesiowüstite, respectively (2). With the rapid increase in the use of broadband seismometers and seismic arrays, seismologists have been able to determine the depths of the 400-and 670-km discontinuities and their lateral variation with increasingly finer resolutions (3). To correlate the observed seismic variability with the compositional and thermal variations in the mantle, we have to be able to determine mantle phase transitions with high accuracy, better than 1% in pressure determination (i.e., Ϯ0.25 GPa at 25 GPa). Similarly, it is critically dependent on the accuracy in pressure determination whether or not the recently discovered postperovskite transition (4, 5) indeed occurs at the base of the lower mantle and accounts for a number of seismic anomalies observed in the DЉ region. Because the DЉ layer is observed in a narrow depth int...

No abstract

In the last few years, the superconducting transition temperature, Tc, of hydrogen-rich compounds has increased dramatically, and is now approaching room temperature. However, the pressures at which these materials are stable exceed one million atmospheres and limit the number of available experimental probes - superconductivity has been primarily identified based on electrical transport measurements. Here, we report definitive evidence of the Meissner effect – a key feature of superconductivity – in H3S and LaH10. Furthermore, we have determined characteristic superconducting parameters: a lower critical field Hc1 of ∼1.9 and ∼1.0 T, and a London penetration depth λL of ∼13 and ∼21 nm in Im-3m-H3S and Fm-3m-LaH10, respectively. These compounds have low values of the Ginzburg-Landau parameter κ ∼7–14 and belong to the group of “moderate” type II superconductors.

No abstract

Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single-crystal X-ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.

In order to intercalibrate the equations of state (EOSs) of the three widely used pressure standards, gold, platinum, and MgO, we have measured their unit cell volumes together in the laser‐heated diamond anvil cell up to 140 GPa and 2500 K. At 300 K, three standards agree with each other within ±2.5 GPa to 135 GPa if the EOSs measured in quasi‐hydrostatic media are used. We further refined the EOSs at 300 K, making them consistent with each other within ±1 GPa up to 135 GPa. At high temperature (T), the three standards match the best within ±1 GPa between 40 and 140 GPa, when we use the scales by Dorogokupets and Dewaele (2007). However, a 2–3 GPa discrepancy remains at 20–40 GPa and 1500–2000 K, with gold yielding the highest pressure (P). The pressure discrepancy is likely related to steep decreases in the Grüneisen parameter, the anharmonicity, and/or the electronic effects for the standards at the P‐T conditions. Because gold melts near the temperatures expected for the mantle transition zone, severe anharmonic effects expected under premelting conditions make gold unsuitable for determining the phase boundaries in the region. The pressure scales by Dorogokupets and Dewaele (2007) provide tighter constrains on the Clapeyron slopes of the postspinel boundary to −2.0 to −2.7 MPa/K and the postperovskite boundary to 7–10 MPa/K. The data and refined EOSs presented here allow for reliable comparisons among experiments with different pressure standards for the entire P‐T conditions expected for the Earth's lower mantle.

We describe the synthesis of nitrides of iridium and palladium using the laser-heated diamond anvil cell. We have used the in-situ techniques of x-ray powder diffraction and Raman scattering to characterize these compounds and have compared our experimental findings where possible to the results of first-principles theoretical calculations. We suggest that palladium nitride is isostructural with pyrite while iridium nitride has a monoclinic symmetry and may be isostructural with baddeleyite.

What prompted you to investigate this topic/problem? Scientific knowledge and our understanding of nature are built upon collected empirical evidence and regularities found in similar systems. We have been pursuing systematic, high-pressure research on binary non-metal nitrides and found that there is a gap in our understanding of the crystal chemistry of pnictogen group element nitrides; we were missing XN 6 structural units known in high-pressure carbon group elements and chalcogen nitrides (e.g., in SiN 2 , GeN 2 , SnN 2 , and SN 2 ). In our work, with the high-pressure synthesis and the identification of the d-P 3 N 5 and PN 2 compounds, both featuring the desired PN 6 octahedra, the problem was resolved, and the common regularities within the whole group of binary non-metal nitrides were established.