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Paper about high pressure behavior of pyrope garnet by Yi Hu et al. published in JGR

Pyrope is an Mg end-member garnet, which constitutes up to ~15% of the upper mantle. Thermodynamic and thermoelastic properties of garnet at high pressure and high temperature are important for understanding the composition and structure of the Earth. Here we report the first-principles calculations of vibrational properties, thermodynamic properties, and elasticity of pyrope over a wide pressure and temperature range. The calculated results exhibit good consistency with the available experimental results and provide values up to the pressure and temperature range that are challenging for experiments to achieve and measure. Pyrope is almost isotropic at high pressure. The elastic moduli, especially the shear modulus of pyrope, exhibit nonlinear pressure and temperature dependences. Density and seismic velocities of pyrope along with piclogite, pyrolite, and eclogite are compared with seismic models along the normal upper mantle and the cold subducting lithospheric plate geotherms. Pyrope has the highest density and seismic velocities among the major minerals of the upper mantle along these geotherms. Eclogite with 30% pyrope and 70% clinopyroxene is denser than the surrounding mantle even along the normal upper mantle geotherm and becomes still denser along the cold slab geotherm. Seismic velocities of eclogite with 30% pyrope along the normal upper mantle geotherm are slower than the surrounding mantle but along the cold slab geotherm are faster than the surrounding mantle.
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Paper about high pressure behavior of fayalite Fa100 by Jin Zhang et al. published in PCM

Olivine is widely believed to be the most abundant mineral in the Earth’s upper mantle. Here, we report structural refinement results for the Fe-end-member olivine, Fe2SiO4 fayalite, up to 31 GPa in diamond-anvil cell, using single-crystal synchrotron X-ray diffraction. Unit-cell parameters a, b, c and V, average Si–O Fe–O bond lengths, as well as Si–O Fe–O polyhedral volumes continuously decrease with increasing pressure. The pressure derivative of isothermal bulk modulus K′ T0 is determined to be 4.0 (2) using third-order Birch–Murnaghan equation of state with ambient isothermal bulk modulus fixed to 135 GPa on the basis of previous Brillouin measurements. The Si–O tetrahedron is stiffer than the Fe–O octahedra, and the compression mechanism is dominated by Fe–O bond and Fe–O octahedral compression. Densities of olivine along 1600 and 900 K adiabats are calculated based on this study. The existence of metastable olivine inside the cold subduction slab could cause large positive buoyancy force against subduction, slow down the subduction and possibly affect the slab geometry.
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Paper about pressure-induced changes in optical properties of hybrid organic-inorganic perovskite photovoltaic by Kong et al. published in PNAS

Organic–inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley–Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (70% to 100% increase) under mild pressures at ~0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon–electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance.
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Paper about high pressure bevavior of omphacite to 47 GPa by Dongzhou Zhang et al. published in PCM

Omphacite is an important mineral component of eclogite. Single-crystal synchrotron X-ray diffraction data on natural (Ca, Na) (Mg, Fe, Al)Si2O6 omphacite have been collected at the Advanced Photon Source beamlines 13-BM-C and 13-ID-D up to 47 GPa at ambient temperature. Unit cell parameter and crystal structure refinements were carried out to constrain the isothermal equation of state and compression mechanism. The third-order Birch– Murnaghan equation of state (BM3) fit of all data gives V0 = 423.9(3) Å3, KT0 = 116(2) GPa and KT0′ = 4.3(2). These elastic parameters are consistent with the general trend of the diopside–jadeite join. The eight-coordinated polyhedra (M2 and M21) are the most compressible and contribute to majority of the unit cell compression, while the SiO4 tetrahedra (Si1 and Si2) behave as rigid structural units and are the most incompressible. Axial compressibilities are determined by fitting linearized BM3 equation of state to pressure dependences of unit cell parameters. Throughout the investigated pressure range, the b-axis is more compressible than the c-axis. The axial compressibility of the a-axis is the largest among the three axes at
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X-ray Atlas instrument installed at HIGP

X-ray Atlas advanced diffractometer system, funded by the NSF EAR instrumetation grant has been installed in HIG room 154. The system consists of Bruker D8 Venture single crystal diffractometer and D8 Advance powder diffractometer. Both instruments are equipped with variable temperature devices. D8 Venture features innovative components such as PHOTON II CPAD detector and Incoatec ImS 3.0 Ag microfocus source with Helios focusing optics, and is being further customized for high-pressure experiements, including online ruby fluorescence measurments, heavy duty sample platform and membrane-driven pressure control system. Both instruments will be available for both collaborative as well as service work startin in September 2016.

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Paper about new high pressure phase of Be(OH)2 and its relation to SiO2 cristobalite by Hannah Shelton et al. published in PCM

Three isotypic crystals, SiO2 (α-cristobalite), ε-Zn(OH)2 (wülfingite) and Be(OH)2 (β-behoite), with topologically identical frameworks of corner-connected tetrahedra, undergo displacive compression-driven phase transitions at similar pressures (1.5-2.0 GPa), but each transition is characterized by a different mechanism resulting in different structural modifications. In this study, we report the crystal structure of the high-pressure γ-phase of beryllium hydroxide and compare it with the high-pressure structures of the other two minerals. In Be(OH)2, the transition from the ambient β-behoite phase with the orthorhombic space group P212121 and ambient unit cell parameters a = 4.5403(4) Å, b = 4.6253(5) Å, c = 7.0599(7) Å, to the high-pressure orthorhombic γ-polymorph with space group Fdd2 and unit cell parameters (at 5.3(1) GPa) a = 5.738(2) Å, b = 6.260(3) Å, c = 7.200(4) Å takes place between 1.7 and 3.6 GPa. This transition is essentially second order, is accompanied by a negligible volume discontinuity, and exhibits both displacive and reversible character. The mechanism of the phase transition results in a change to the hydrogen bond connectivities and rotation of the BeO4 tetrahedra.
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Paper about pressure-induced change in optical properties of B4.3C by Hushur et al. published in J. of Physics

Single-crystal B4.3C boron carbide is investigated through the pressure-dependence and inter-relation of atomic distances, optical properties and Raman-active phonons up to ~70GPa. The anomalous pressure evolution of the gap width to higher energies is striking. This is obtained from observations of transparency, which most rapidly increases around 55GPa. Full visible optical transparency is approached at pressures of>60GPa indicating that the band gap reaches ~3.5eV; at high pressure, boron carbide is a wide-gap semiconductor. The reason is that the high concentration of structural defects controlling the electronic properties of boron carbide at ambient conditions initially decreases and finally vanishes at high pressures. The structural parameters and Raman-active phonons indicate a pressure-dependent phase transition in single-crystal natB4.3C boron carbide near 40GPa, likely related to structural changes in the C–B–C chains, while the basic icosahedral structure appears to be less affected.
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CDAC approves funding for our group for 2016-2017 academic year

The CDAC-supported project at the University of Hawaii started on September 1, 2013. This proposal request renewal of funding for the fourth year. Currently two Ph.D. students are supported by this project, each at 50%: Yi Hu (B.Sc. from University of Science and Technology of China, major in geophysics, started the Ph.D. program at UH in August 2013) and Hanna Shelton (B.Sc. from University of Hawaii, major in chemistry, started the Ph.D. program on September 1, 2014). Since the beginning of the project our efforts have been focused on training the students in high-pressure techniques, sample preparation, principles of high-pressure X-ray crystallography and data analysis and crystallographic computations.
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NSF awards grant to develop X-ray Atlas instrument

X-ray Atlas instrument, being developed within the NSF EAR Instrumentation and Facilities project through acquisition of Bruker D8 Venture/D8 Advance system and further customization, will create a novel state of the art solution for in situ laboratory-based single-crystal and powder X-ray diffraction experiments at the University of Hawaii. The new instrument system will be capable of exploring pressure-temperature conditions relevant for the Earth upper mantle, transition zone and some of the lower mantle. X-ray Atlas will create new and very exciting opportunities for lab-based mineralogy, petrology and mineral physics undergraduate and graduate research and education, and will serve as personnel training and new technology prototyping site for HIGP-lead projects at Argonne National Laboratory.
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Yi Hu passess Comprehensive Exam

On February 1, 2016 Yi Hu successfully passed her PhD Comprehensive Exam. Congratulations Yi!!!
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Dalton Transactions paper about spin transition in Co2+ metalorganic by Miller et al. published

The application of pressure on CoII(dpzca)2, which at ambient pressure undergoes abrupt spin crossover(SCO) with thermal hysteresis, gives unique insights into SCO. It reversibly separates the crystallographicphase transition (I41/a↔P21/c) and associated abrupt SCO from the underlying gradual SCO, as shownby detailed room temperature (RT) X-ray crystallography and temperature dependent magnetic suscepti-bility studies, both under a range of 10 different pressures. The pressure effects are shown to be reversible.The crystal structure of the pressure-induced low-spin state is determined at RT at 0.42(2) and 1.78(9)GPa. At the highest pressure of 1.78(9) GPa the Co–N bond lengths are consistent with the complex beingfully LS, and the conjugated terdentate ligands are significantly distorted out of plane. The abrupt SCOevent can be shifted up to RT by application of a hydrostatic pressure of 0.4 GPa. These magnetic sus-ceptibility (vs.temperature) and X-ray crystallography (at RT) studies, under a range of pressures, showthat the SCO can be tuned over a wide range of temperature and pressure space, including RT SCO.
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Paper about hydrous wadsleyite and ringwoodite in the transition zone by Yin-Yuan Chang et al. published in JGR

Review of recent mineral physics literature shows consistent trends for the influence of Fe and H2O on the bulk modulus (K0) of wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410–660km). However, there is little consensus on the first pressure derivative, K0′=(dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0′ in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H2O on K0′ for wadsleyite and ringwoodite by conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 wadsleyite containing 2.0 and 0.25 wt% H2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4 wt% H2O. By measuring their pressure-volume evolution simultaneously up to 32GPa, we constrain the difference in K0′ independent of the pressure scale, finding that H2O has no effect on K0′, whereas the effect of H2O on K0 is significant. The fitted K0′ values of hydrous wadsleyite (0.25 and 2.0 wt% H2O) and hydrous ringwoodite (1.4 wt% H2O) examined in this study were found to be identical within uncertainty, with K0′ ~3.7(2). New secondary-ion mass spectrometry measurements of the H2O content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7.0(5) GPa/wt% H2O, independent of Fe content for upper mantle compositions. Because K0′ is unaffected by H2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high-resolution, regional seismology studies.
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Paper about thermal equation of state of bridgmanite by Aaron Wolf et al. published in JGR

The high-pressure/high-temperature equation of state (EOS) of synthetic 13% Fe-bearing bridgmanite (Mg silicate perovskite) is measured using powder X-ray diffraction in a laser-heated diamond anvil cell with a quasi-hydrostatic neon pressure medium. We compare these results, which are consistent with previous 300 K sound speed and compression studies, with a reanalysis of Fe-free Mg end-member data from Tange et al. (2012) to determine the effect of iron on bridgmanite's thermoelastic properties. EOS parameters are incorporated into an ideal lattice mixing model to probe the behavior of bridgmanite at deep mantle conditions. With this model, a nearly pure bridgmanite mantle composition is shown to be inconsistent with density and compressibility profiles of the lower mantle. We also explore the buoyant stability of bridgmanite over a range of temperatures and compositions expected for Large Low-Shear Velocity Provinces, concluding that bridgmanite-dominated thermochemical piles are more likely to be passive dense layers externally supported by convection, rather than internally supported metastable domes. The metastable dome scenario is estimated to have a relative likelihood of only 4–7%, given the narrow range of compositions and temperatures consistent with seismic constraints. If buoyantly supported, such structures could not have remained stable with greater thermal contrast early in Earth's history, ruling out formation scenarios involving a large concentration of heat producing elements.
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