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Knowledge of the thermal conductivity of Ar under conditions of high pressures and temperatures (P-T) is important for model calculations of heat transfer in the laser heated diamond anvil cell (DAC) as it is commonly used as a pressure transmitting medium and for thermal insulation. We used a modified transient heating technique utilizing microsecond laser pulses in a symmetric DAC to determine the P-T dependent thermal conductivity of solid Ar up to 50 GPa and 2500 K. The temperature dependent thermal conductivity of Ar was obtained by fitting the results of finite element calculations to the experimentally determined time dependent temperature of a thin Ir foil surrounded by Ar. Our data for the thermal conductivity of Ar are larger than that theoretically calculated using the Green-Kubo formalism, but they agree well with those based on kinetic theory. These results are important for ongoing studies of the thermal transport properties of minerals at pressures and temperatures native to the mantle and core. [ABSTRACT FROM AUTHOR]

Melting of boron subphosphide (B12P2) to 26 GPa has been studied byin situsynchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and by quenching and electrical resistance measurements in a toroid-type high pressure apparatus. B12P2melts congruently, and the melting curve has a positive slope of 23(6) K/GPa. No solid-state phase transition was observed up to the melting in the whole pressure range under study. [ABSTRACT FROM PUBLISHER]

Series of high-pressure x-ray diffraction patterns of iron and its high-pressure polymorphs were collected with 0.1-0.2-s exposure time utilizing a membrane diamond anvil cell (DAC) for compression at various loading and unloading rates to a maximum pressure of 70 GPa. Strain rates of 10-2s-1 at a maximum pressurization rate of 4.1 GPa/s were achieved in non-hydrostatic compression of hcp Fe. Linewidth analysis was used to retrieve strain and uniaxial stress of Fe as a function of pressure upon both compression and decompression. Analysis of the lattice parameters ratio c/a of hcp Fe indicates the presence of complex non-hydrostatic stress states, which developed as a function of strain rate, relaxation time, and various levels of hydrostaticity. Our results emphasize the importance of a controlled pressurization in DACs because the experimental loading rate strongly influences the stress state of the sample, particularly on decompression. Our time-resolved x-ray diffraction of the phase transition from bcc Fe to hcp Fe reveals residual grains of bcc Fe capable of surviving to very high pressures (>35 GPa) for a few minutes after the transition. [ABSTRACT FROM AUTHOR]

We investigated the properties of Al-bearing SiO2 (with 4 or 6 wt% Al2O3) at pressures and temperatures corresponding to the lowermost mantle, using laser-heated diamond-anvil cell coupled with synchrotron-based in situ X-ray diffraction. The phase transition from CaCl2-structured to α-PbO2- structured (seifertite) polymorphs occurs between 113 and 119 GPa at 2500 K. The range of pressure where the two phases coexist is small. There is a slight decrease of the transition pressure with increasing Al-content. We propose a tentative phase diagram reporting the minerals composition as a function of pressure in the SiO2-Al2O3 system. We also refine the P-V-T equation of state of Al-bearing seifertite based on volume measurements up to more than 160 GPa and 4000 K [V0 = 92.73(10) Å3, K0 = 304.2(3.0) GPa, K'0 = 4.59 (fixed), ɵD0 = 1130 K (fixed), γ0 = 1.61(3)]. At 300 K, the volume decrease at the CaCl2 to α-PbO2 transition is 0.5(1)%, a value slightly lower than the 0.6% reported previously for Al-free samples. At high temperature, the Grüneisen parameter of seifertite is found to be similar to that of stishovite. Nevertheless, the ▵ V/V across the CaCl2-form to seifertite transition is found to increase slightly with increasing temperature. Across the phase transition, volume changes can be translated into density changes only when the Al substitution mechanisms in both CaCl2-form and seifertite are defined. The analysis of all available data sets suggests different substitution mechanisms for the two SiO2 polymorphs. Al-substitution could occur via O-vacancies in the CaCl2-form and via extra interstitial Al in seifertite. This would result in a density increase of 2.2(3)% at 300 K for SiO2 in basaltic lithologies. Alternatively, the same Alsubstitution mechanism in both of the SiO2-dominated phases would yield a density increase of 0.5(1)%. [ABSTRACT FROM AUTHOR]

A novel high pressure polymorph of iron sesquioxide,m-Fe2O3, has been identified by means of single-crystal synchrotron X-ray diffraction (XRD). Upon compression of a single crystal of hematite, α-Fe2O3, in a diamond anvil cell, the transition occurs at pressure of about 54 GPa and results in ∼10% volume reduction. The crystal structure of the new phase was solved by the direct method (monoclinic space groupP21/n, a=4.588(3),b=4.945(2),c=6.679(7) Å and β=91.31(9)°) and refined toR1∼11%. It belongs to the cryolite double-perovskite structure type and consists of corner-linked FeO6octahedra and FeO6trigonal prisms filling the free space between the octahedra. Upon compression up to ∼71 GPa at ambient temperature no further phase transitions were observed. Laser heating to ∼ 2100±100 K promotes a transition to theCmcmCaIrO3-type (post-perovskite (PPv)) phase. The PPv-Fe2O3crystal structure was refined by means of single-crystal XRD at ∼65 GPa. On decompression the PPv-Fe2O3phase fully transforms back to hematite at pressures between ∼25 and 15 GPa. [ABSTRACT FROM PUBLISHER]

The cubic diamond (Fd 3 ‾ m) group IVA element Si has been the material driver of the electronics industry since its inception. We report synthesis of a new cubic (Im 3 ‾ m) group IVA material, a GeSn solid solution, upon heating Ge and Sn at pressures from 13 to 28 GPa using double-sided diamond anvil laser-heating and large volume press methods. Both methods were coupled with in situ angle dispersive X-ray diffraction characterization. The new material substantially enriches the seminal group IVA alloy materials landscape by introducing an eightfold coordinated cubic symmetry, which markedly expands on the conventional tetrahedrally coordinated cubic one. This cubic solid solution is formed, despite Ge never adopting the Im 3 ‾ m symmetry, melting inhibiting subsequent Im 3 ‾ m formation and reactant Ge and Sn having unlike crystal structures and atomic radii at all these pressures. This is hence achieved without adherence to conventional formation criteria and routes to synthesis. This advance creates fertile avenues for new materials development., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)