High pressure chemical reactivity and structural study of the Na-P and Li-P systems

Pressure enables the synthesis of (Na/Li)3P compounds at RT bypassing established chemical methods while at higher pressure, both undergo a pressure-induced phase transition.</p

High pressure chemical reactivity and structural study of the Na-P and Li-P systems

Pressure enables the synthesis of (Na/Li)3P compounds at RT bypassing established chemical methods while at higher pressure, both undergo a pressure-induced phase transition.</p

Single crystal elasticity of majoritic garnets: Stagnant slabs and thermal anomalies at the base of the transition zone

The elastic properties of two single crystals of majoritic garnet (Mg3.24Al1.53Si3.23O12 and Mg3.01Fe0.17Al1.68Si3.15O12), have been measured using simultaneously single-crystal X-ray diffraction and Brillouin spectroscopy in an externally heated diamond anvil cell with Ne as pressure transmitting medium at conditions up to ∼30 GPa and ∼600 K. This combination of techniques makes it possible to use the bulk modulus and unit-cell volume at each condition to calculate the absolute pressure, independently of secondary pressure calibrants. Substitution of the majorite component into pyrope garnet lowers both the bulk (Ks) and shear modulus (G). The substitution of Fe was found to cause a small but resolvable increase in Ks that was accompanied by a decrease in ∂Ks/∂P, the first pressure derivative of the bulk modulus. Fe substitution had no influence on either the shear modulus or its pressure derivative. The obtained elasticity data were used to derive a thermo-elastic model to describe Vs and Vp of complex garnet solid solutions. Using further elasticity data from the literature and thermodynamic models for mantle phase relations, velocities for mafic, harzburgitic and lherzolitic bulk compositions at the base of Earth's transition zone were calculated. The results show that Vs predicted by seismic reference models are faster than those calculated for all three types of lithologies along a typical mantle adiabat within the bottom 150 km of the transition zone. The anomalously fast seismic shear velocities might be explained if laterally extensive sections of subducted harzburgite-rich slabs pile up at the base of the transition zone and lower average mantle temperatures within this depth range

Size-dependent pressure-induced amorphization in nanoscale TiO2

We investigated the size-dependent high-pressure phase transition behavior of nanocrystalline anatase TiO2 with synchrotron x-ray diffraction and Raman spectroscopy to 45 GPa at ambient temperature. Pressure-induced amorphization results in a high-density amorphous (HDA) form when the starting crystallite size is <10nm. The HDA-TiO2 transforms to a low-density amorphous form at lower pressures. Harnessing the nanometer length scale thus provides a new window for experimental investigation of amorphization in poor glass formers and a synthesis route for new amorphous materials. © 2006 The American Physical Society

Compression behavior of VC0:85 up to 53 GPa

Samples of VC0:85 sandwiched between aluminum disks were compressed in a diamond anvil cell and X-ray diffraction patterns recorded at high pressures up to 53 GPa using synchrotron radiation. The presence of aluminum in the cell rendered the sample pressure nearly hydrostatic and also served as the pressure standard. No phase transformation was observed up to the highest pressure. The measured unit cell volume versus pressure data gave 258 xB1; 11 GPa and 4.5 xB1; 0.6 for the bulk modulus and the pressure derivative, respectively

Phase stability of iron germanate, FeGeO3, to 127&nbsp;GPa

The high-pressure behavior of germanates is of interest as these compounds serve as analogs for silicates of the deep Earth. Current theoretical and experimental studies of iron germanate, FeGeO3, are limited. Here, we have examined the behavior of FeGeO3 to 127 GPa using the laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. Upon compression at room temperature, the ambient-pressure clinopyroxene phase transforms to a disordered triclinic phase [FeGeO3 (II)] at ~ 18 GPa in agreement with earlier studies. An additional phase transition to FeGeO3 (III) occurs above 54 GPa at room temperature. Laser-heating experiments (~ 1200–2200&nbsp;K) were conducted at three pressures (33, 54, and 123&nbsp;GPa) chosen to cover the stability regions of different GeO2 polymorphs. In all cases, we observe that FeGeO3 dissociates into GeO2 + FeO at high pressure and temperature conditions. Neither the perovskite nor the post-perovskite phase was observed up to 127&nbsp;GPa at ambient or high temperatures. The results are consistent with the behavior of FeSiO3, which also dissociates into a mixture of the oxides (FeO + SiO2) at least up to 149&nbsp;GPa

Liebermannite, KAlSi3O8, a new shock-metamorphic, high-pressure mineral from the Zagami Martian meteorite

In this paper, we discuss the occurrence of liebermannite (IMA 2013-128), KAlSi3O8, a new, shock-generated, high-pressure tetragonal hollandite-type structure silicate mineral, in the Zagami basaltic shergottite meteorite. Liebermannite crystallizes in space group I4/m with Z&nbsp;=&nbsp;2, cell dimensions of a&nbsp;=&nbsp;9.15&nbsp;±&nbsp;0.14 (1σ)&nbsp;Å, c&nbsp;=&nbsp;2.74&nbsp;±&nbsp;0.13&nbsp;Å, and a cell volume of 229&nbsp;±&nbsp;19&nbsp;Å3 (for the type material), as revealed by synchrotron diffraction. In Zagami, liebermannite likely formed via solid-state transformation of primary igneous K-feldspar during an impact event that achieved pressures of ~20&nbsp;GPa or more. The mineral name is in honor of Robert C. Liebermann, a high-pressure mineral physicist at Stony Brook University, New York, USA

Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms

Although the crystal structure of the high-pressure SiO2 polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser-heated diamond anvil cell and compressed the stishovite aggregate up to 38&nbsp;GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation and find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip

Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms

Although the crystal structure of the high-pressure SiO2 polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser-heated diamond anvil cell and compressed the stishovite aggregate up to 38&nbsp;GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation and find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip