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We conducted an in-situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite,... more
We conducted an in-situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe2, was studied under high pressures up to 46 GPa and low temperatures, down to 50 K using single-crystal microdiffraction techniques. High pressure and low temperatures were generated using a diamond anvil cell and a cryostat. We found no evidences of structural instability in the explored P-T space. The deformation of the orthorhombic lattice is slightly anisotropic. As expected, the compressibility of the Se-Se dumbbell, the longer bond in the structure, is larger than that of the Fe-Se bonds. Less obvious is the behavior of the octahedral bonds, the shorter bond is the most compressible determining a small increase in the octahedron distortion with pressure. We also achieved a robust structural analysis of ferroselite at low t...
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We report real-time observations of a phase transition in the ionic solid CaF_{2}, a model AB_{2} structure in high-pressure physics. Synchrotron x-ray diffraction coupled with dynamic loading to 27.7 GPa, and separately with static... more
We report real-time observations of a phase transition in the ionic solid CaF_{2}, a model AB_{2} structure in high-pressure physics. Synchrotron x-ray diffraction coupled with dynamic loading to 27.7 GPa, and separately with static compression, follows, in situ, the fluorite to cotunnite structural phase transition, both on nanosecond and on minute time scales. Using Rietveld refinement techniques, we examine the kinetics and hysteresis of the transition. Our results give insight into the kinetic time scale of the fluorite-cotunnite phase transition under shock compression, which is relevant to a number of isomorphic compounds.
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We have designed and constructed a new system for micro-machining parts and sample assemblies used for diamond anvil cells and general user operations at the High Pressure Collaborative Access Team, sector 16 of the Advanced Photon... more
We have designed and constructed a new system for micro-machining parts and sample assemblies used for diamond anvil cells and general user operations at the High Pressure Collaborative Access Team, sector 16 of the Advanced Photon Source. The new micro-machining system uses a pulsed laser of 400 ps pulse duration, ablating various materials without thermal melting, thus leaving a clean edge. With optics designed for a tight focus, the system can machine holes any size larger than 3 μm in diameter. Unlike a standard electrical discharge machining drill, the new laser system allows micro-machining of non-conductive materials such as: amorphous boron and silicon carbide gaskets, diamond, oxides, and other materials including organic materials such as polyimide films (i.e., Kapton). An important feature of the new system is the use of gas-tight or gas-flow environmental chambers which allow the laser micro-machining to be done in a controlled (e.g., inert gas) atmosphere to prevent oxi...
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Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The... more
Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not...
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Physical properties of lithium under extreme pressures continuously reveal unexpected features. These include a sequence of structural transitions to lower symmetry phases, metal-insulator-metal transition, superconductivity with one of... more
Physical properties of lithium under extreme pressures continuously reveal unexpected features. These include a sequence of structural transitions to lower symmetry phases, metal-insulator-metal transition, superconductivity with one of the highest elemental transition temperatures, and a maximum followed by a minimum in its melting line. The instability of the bcc structure of lithium is well established by the presence of a temperature-driven martensitic phase transition. The boundaries of this phase, however, have not been previously explored above 3 GPa. All higher pressure phase boundaries are either extrapolations or inferred based on indirect evidence. Here we explore the pressure dependence of the martensitic transition of lithium up to 7 GPa using a combination of neutron and X-ray scattering. We find a rather unexpected deviation from the extrapolated boundaries of the hR3 phase of lithium. Furthermore, there is evidence that, above ∼3 GPa, once in fcc phase, lithium does ...
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Complementary advances in high pressure research apparatus and techniques make it possible to carry out time-resolved high pressure research using what would customarily be considered static high pressure apparatus. This work specifically... more
Complementary advances in high pressure research apparatus and techniques make it possible to carry out time-resolved high pressure research using what would customarily be considered static high pressure apparatus. This work specifically explores time-resolved high pressure x-ray diffraction with rapid compression and/or decompression of a sample in a diamond anvil cell. Key aspects of the synchrotron beamline and ancillary equipment are presented, including source considerations, rapid (de)compression apparatus, high frequency imaging detectors, and software suitable for processing large volumes of data. A number of examples are presented, including fast equation of state measurements, compression rate dependent synthesis of metastable states in silicon and germanium, and ultrahigh compression rates using a piezoelectric driven diamond anvil cell.
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The ability to remotely control pressure in diamond anvil cells (DACs) in accurate and consistent manner at room temperature, as well as at cryogenic and elevated temperatures, is crucial for effective and reliable operation of a... more
The ability to remotely control pressure in diamond anvil cells (DACs) in accurate and consistent manner at room temperature, as well as at cryogenic and elevated temperatures, is crucial for effective and reliable operation of a high-pressure synchrotron facility such as High Pressure Collaborative Access Team (HPCAT). Over the last several years, a considerable effort has been made to develop instrumentation for remote and automated pressure control in DACs during synchrotron experiments. We have designed and implemented an array of modular pneumatic (double-diaphragm), mechanical (gearboxes), and piezoelectric devices and their combinations for controlling pressure and compression/decompression rate at various temperature conditions from 4 K in cryostats to several thousand Kelvin in laser-heated DACs. Because HPCAT is a user facility and diamond cells for user experiments are typically provided by users, our development effort has been focused on creating different loading mecha...
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Naturally oxidized uranium has been compressed using a diamond anvil cell. Although X-ray diffraction shows the anisotropic nature in the pressure dependent changes to the lattice parameters of pure uranium as previously recorded, uranium... more
Naturally oxidized uranium has been compressed using a diamond anvil cell. Although X-ray diffraction shows the anisotropic nature in the pressure dependent changes to the lattice parameters of pure uranium as previously recorded, uranium oxide appears stable at high pressure in the fluorite structure with no clear evidence of a phase transition observed above the transition pressure previously measured for
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ABSTRACT The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon. In... more
ABSTRACT The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon. In this study, these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambient pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of . These data were used to construct diagrams of the metastability regimes of the polymorphs formed in a DAC and may prove useful for potential technological applications of these metastable polymorphs.
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Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations... more
Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations undergo same pressure-induced phase transitions but at progressively lower pressures as the cation radii increases. However, we discovered that this conventional law reverses in the structural transitions in 122-type iron-based superconductors. In this report, a combined low temperature and high pressure X-ray diffraction (XRD) measurement has identified the phase transition curves among the tetragonal (T), orthorhombic (O) and the collapsed-tetragonal (cT) phases in the structural phase diagram of the iron-based superconductor AFe2As2 (A = Ca, Sr, Eu, and Ba). The cation radii dependence of the phase transition pressure (T → cT) shows an opposite trend in which the compounds with larger ambient radii cations have a higher transition pressure.
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We present a new design of a universal diamond anvil cell, suitable for different kinds of experimental studies under high pressures. Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability,... more
We present a new design of a universal diamond anvil cell, suitable for different kinds of experimental studies under high pressures. Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability, making the presented cell design suitable for a whole range of techniques from optical absorption to single-crystal X-ray diffraction studies, also in combination with external resistive or double-side laser heating. Three examples of the cell applications are provided: a Brillouin scattering of neon, single-crystal X-ray diffraction of α-Cr2O3, and resistivity measurements on the (Mg0.60Fe0.40)(Si0.63Al0.37)O3 silicate perovskite.
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... [2] CS Zha, RJ Hemley, HK Mao, TS Duffy and C. Meade. Phys. Rev. B, 50 (1994), p. 13105. [3] M. Grimsditch. Phys. Rev. Lett., 52 (1984), p. 2379. [4] M. Grimsditch, R. Bhadra and Y. Meng. Phys. Rev. B, 38 (1988), p. 7836. [5] O.... more
... [2] CS Zha, RJ Hemley, HK Mao, TS Duffy and C. Meade. Phys. Rev. B, 50 (1994), p. 13105. [3] M. Grimsditch. Phys. Rev. Lett., 52 (1984), p. 2379. [4] M. Grimsditch, R. Bhadra and Y. Meng. Phys. Rev. B, 38 (1988), p. 7836. [5] O. Mishima, LD Calvert and E. Whalley. ...
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ABSTRACT Quantitative high pressure neutron-diffraction measurements have traditionally required large sample volumes of at least ∼25 mm3 due to limited neutron flux. Therefore, pressures in these experiments have been limited to below 25... more
ABSTRACT Quantitative high pressure neutron-diffraction measurements have traditionally required large sample volumes of at least ∼25 mm3 due to limited neutron flux. Therefore, pressures in these experiments have been limited to below 25 GPa. In comparison, for X-ray diffraction, sample volumes in conventional diamond cells for pressures up to 100 GPa have been less than 1×10−4 mm3. Here, we report a new design of strongly supported conical diamond anvils for neutron diffraction that has reached 94 GPa with a sample volume of ∼2×10−2 mm3, a 100-fold increase. This sample volume is sufficient to measure full neutron-diffraction patterns of D2O–ice to this pressure at the high flux Spallation Neutrons and Pressure beamline at the Oak Ridge National Laboratory. This provides an almost fourfold extension of the previous pressure regime for such measurements.
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High‐pressure safety valves with set pressures of more than 200 bar are required in industry, e.g. for polyethylene and synthesis gas applications. They are presently sized according to ISO 4126‐1. Only equations for ideal gases are... more
High‐pressure safety valves with set pressures of more than 200 bar are required in industry, e.g. for polyethylene and synthesis gas applications. They are presently sized according to ISO 4126‐1. Only equations for ideal gases are presented there, and there are no indications as to how the real gas factor and the adiabatic exponent for real gases are to be calculated. For this reason, an equation for the critical mass flow rate of a real gas through a nozzle was derived and compared with the model according to EN‐ISO 4126‐1 and with experimental data. It is recommended that the current ISO‐standard be supplemented by the nozzle flow model for real gases. The first numerical calculations (ANSYS‐CFX) show that the discharge coefficient for a high pressure safety valve measured at moderate pressures can be extrapolated to very high pressures if it is used in conjunction with the nozzle flow model for real gases. However, this numerical result must yet be validated for further valve t...
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Abstract We report here the pressure dependence of the electrical resistivity and magnetic susceptibility of polycrystalline Ce 0.6 Y 0.4 FeAsO 0.8 F 0.2 superconductor in the temperature range 4 K to 300 K up to 8 GPa. In-situ high... more
Abstract We report here the pressure dependence of the electrical resistivity and magnetic susceptibility of polycrystalline Ce 0.6 Y 0.4 FeAsO 0.8 F 0.2 superconductor in the temperature range 4 K to 300 K up to 8 GPa. In-situ high pressure-low temperature x-ray ...
Research Interests: Engineering, Physics, Condensed Matter Physics, Materials Science, High Pressure, and 14 moreSuperconductivity, Applied Physics, X Rays, Synchrotron, Physical sciences, Superconductors, Electrical Resistance, Magnetic Susceptibility, Iron, X ray diffraction, Structural Properties, Low Temperature, Electric Conductivity, and Transition Temperature
We report an in situ Raman study of KClO4 irradiated with x-rays in a diamond anvil cell. Decomposition via KClO4 + hv → KCl + 2O2 was monitored via the O2 vibron at 2 GPa, 6 GPa, and 9 GPa. For all pressures, the vibron grew in intensity... more
We report an in situ Raman study of KClO4 irradiated with x-rays in a diamond anvil cell. Decomposition via KClO4 + hv → KCl + 2O2 was monitored via the O2 vibron at 2 GPa, 6 GPa, and 9 GPa. For all pressures, the vibron grew in intensity and then diminished after successive irradiation suggesting that O2 was diffusing away from the irradiated region. Surprisingly, the diffusion rate accelerated with pressure increase, indicating that the nonhydrostatic pressure gradient was likely driving molecular diffusion of oxygen. At 9 GPa, the vibron bifurcated suggesting that O2 exists as two forms: interstitial and bulk solid. This method can be employed to study molecular diffusion under extreme conditions.
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The superconducting CeFe1−xCoxAsO (Co=0.1) oxyarsenide with a transition temperature (Tc) 11.4 K has been investigated by in situ high pressure synchrotron x-ray diffraction, magnetization, and resistivity measurements. The experiments... more
The superconducting CeFe1−xCoxAsO (Co=0.1) oxyarsenide with a transition temperature (Tc) 11.4 K has been investigated by in situ high pressure synchrotron x-ray diffraction, magnetization, and resistivity measurements. The experiments performed at 10 K up to 6 GPa and at room temperature (RT) up to 55 GPa indicate large anisotropic lattice compression. A pressure induced structural change to a collapsed tetragonal structure is observed above 10 GPa at RT. We report here the enhancement of Tc from 11.4 to 12.3 K with a small increase in pressure up to 0.4 GPa and is first observed in an electron doped Ce-1111 system.