The amount of data collected during synchrotron X-ray diffraction (XRD) experiments is constantly increasing. Most of the time, the data are collected with image detectors, which necessitates the use ...of image reduction/integration routines to extract structural information from measured XRD patterns. This step turns out to be a bottleneck in the data processing procedure due to a lack of suitable software packages. In particular, fast-running synchrotron experiments require online data reduction and analysis in real time so that experimental parameters can be adjusted interactively. Dioptas is a Python-based program for on-the-fly data processing and exploration of two-dimensional X-ray diffraction area detector data, specifically designed for the large amount of data collected at XRD beamlines at synchrotrons. Its fast data reduction algorithm and graphical data exploration capabilities make it ideal for online data processing during XRD experiments and batch post-processing of large numbers of images.
We measure the electrical resistivity of hcp iron up to ∼ 170 GPa and ∼ 3000 K using a four-probe van der Pauw method coupled with homogeneous flattop laser heating in a DAC, and compute its ...electrical and thermal conductivity by first-principles molecular dynamics including electron-phonon and electron-electron scattering. We find that the measured resistivity of hcp iron increases almost linearly with temperature, and is consistent with our computations. The results constrain the resistivity and thermal conductivity of hcp iron to ∼ 80 ± 5 μ Ω cm and ∼ 100 ± 10 W m−1 K−1, respectively, at conditions near the core-mantle boundary. Our results indicate an adiabatic heat flow of ∼ 10 ± 1 TW out of the core, supporting a present-day geodynamo driven by thermal and compositional convection.
WN_{6} phase discovered at 126-165 GPa after heating of W in nitrogen. XRD refinements reveal a unit cell in space group R3over ¯m which is consistent with the WN_{6} structure with armchairlike ...hexazine (N_{6}) rings, while strong A_{1g} Raman mode confirms its N─N single bonds. Density functional theory (DFT) calculations reveal balanced contributions of attractive interactions between W and covalent N_{6} rings, and repulsions between N_{6} rings that make WN_{6} ultrastiff and tough. The WN_{6} phase displays long bond lengths in the nearest N-N and pressure-enhanced electronic band gap, which pave the way for finding novel nitrides.
The discovery of superconducting H
S with a critical temperature T
∼200 K opened a door to room temperature superconductivity and stimulated further extensive studies of hydrogen-rich compounds ...stabilized by high pressure. Here, we report a comprehensive study of the yttrium-hydrogen system with the highest predicted T
s among binary compounds and discuss the contradictions between different theoretical calculations and experimental data. We synthesized yttrium hydrides with the compositions of YH
, YH
, YH
and YH
in a diamond anvil cell and studied their crystal structures, electrical and magnetic transport properties, and isotopic effects. We found superconductivity in the Im-3m YH
and P6
/mmc YH
phases with maximal T
s of ∼220 K at 183 GPa and ∼243 K at 201 GPa, respectively. Fm-3m YH
with the highest predicted T
> 300 K was not observed in our experiments, and instead, YH
was found to be the hydrogen-richest yttrium hydride in the studied pressure and temperature range up to record 410 GPa and 2250 K.
Polymorphism, which describes the occurrence of different lattice structures in a crystalline material, is a critical phenomenon in materials science and condensed matter physics. Recently, ...configuration disorder was compositionally engineered into single lattices, leading to the discovery of high-entropy alloys and high-entropy oxides. For these novel entropy-stabilized forms of crystalline matter with extremely high structural stability, is polymorphism still possible? Here by employing in situ high-pressure synchrotron radiation X-ray diffraction, we reveal a polymorphic transition from face-centred-cubic (fcc) structure to hexagonal-close-packing (hcp) structure in the prototype CoCrFeMnNi high-entropy alloy. The transition is irreversible, and our in situ high-temperature synchrotron radiation X-ray diffraction experiments at different pressures of the retained hcp high-entropy alloy reveal that the fcc phase is a stable polymorph at high temperatures, while the hcp structure is more thermodynamically favourable at lower temperatures. As pressure is increased, the critical temperature for the hcp-to-fcc transformation also rises.
Since invention of the diamond anvil cell technique in the late 1950s for studying materials at extreme conditions, the maximum static pressure generated so far at room temperature was reported to be ...about 400 GPa. Here we show that use of micro-semi-balls made of nanodiamond as second-stage anvils in conventional diamond anvil cells drastically extends the achievable pressure range in static compression experiments to above 600 GPa. Micro-anvils (10-50 μm in diameter) of superhard nanodiamond (with a grain size below ∼50 nm) were synthesized in a large volume press using a newly developed technique. In our pilot experiments on rhenium and gold we have studied the equation of state of rhenium at pressures up to 640 GPa and demonstrated the feasibility and crucial necessity of the in situ ultra high-pressure measurements for accurate determination of material properties at extreme conditions.
Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth's mantle. ...One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ∼ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.
Pressure‐stabilized hydrides are a new rapidly growing class of high‐temperature superconductors, which is believed to be described within the conventional phonon‐mediated mechanism of coupling. ...Here, the synthesis of one of the best‐known high‐TC superconductors—yttrium hexahydride Im3¯m‐YH6 is reported, which displays a superconducting transition at ≈224 K at 166 GPa. The extrapolated upper critical magnetic field Bc2(0) of YH6 is surprisingly high: 116–158 T, which is 2–2.5 times larger than the calculated value. A pronounced shift of TC in yttrium deuteride YD6 with the isotope coefficient 0.4 supports the phonon‐assisted superconductivity. Current–voltage measurements show that the critical current IC and its density JC may exceed 1.75 A and 3500 A mm−2 at 4 K, respectively, which is higher than that of the commercial superconductors, such as NbTi and YBCO. The results of superconducting density functional theory (SCDFT) and anharmonic calculations, together with anomalously high critical magnetic field, suggest notable departures of the superconducting properties from the conventional Migdal–Eliashberg and Bardeen–Cooper–Schrieffer theories, and presence of an additional mechanism of superconductivity.
Novel yttrium hexahydride YH6 is synthesized, an outstanding high‐TC superconductor with critical temperature of 224–226 K and unexpectedly large upper critical magnetic field ≈116–158 T. YH6 demonstrates high critical current density of ≈3500 A mm−2 at 4 K, which is above that of NbTi and YBCO. This study points to a possible additional nonconventional contribution to superconductivity in YH6.
The discovery of superconductivity in H3S at 203 K marked an advance towards room‐temperature superconductivity and demonstrated the potential of H‐dominated compounds to possess a high critical ...temperature (Tc). There have been numerous reports of the H‐S system over the last five years, but important questions remain unanswered. It is crucial to verify whether the Tc was determined correctly for samples prepared from compressed H2S, since they are inevitably contaminated with H‐depleted byproducts. Here, we prepare stoichiometric H3S by direct in situ synthesis from elemental S and excess H2. The Im3‾
m phase of D3S samples exhibits a Tc significantly higher than previously reported values (ca. 150 K), reaching a maximum Tc of 166 K at 157 GPa. Furthermore, we confirm that the sharp decrease in Tc below 150 GPa is accompanied by continuous rhombohedral structural distortions and demonstrate that the Cccm phase is non‐metallic, with molecular H2 units in the crystal structure.
The Im3‾m
phase of stoichiometric D3S, synthesized from elemental S and excess D2 in a diamond anvil cell, exhibits superconductivity with Tc of 166 K at 157 GPa. This is significantly higher than previously reported circa 150 K for samples prepared from disproportionated D2S.
Unexpected Stable Stoichiometries of Sodium Chlorides Zhang, Weiwei; Oganov, Artem R.; Goncharov, Alexander F. ...
Science (American Association for the Advancement of Science),
12/2013, Letnik:
342, Številka:
6165
Journal Article
Recenzirano
Odprti dostop
Sodium chloride (NaCl), or rocksalt, is well characterized at ambient pressure. As a result of the large electronegativity difference between Na and Cl atoms, it has highly ionic chemical bonding ...(with 1:1 stoichiometry dictated by charge balance) and B1-type crystal structure. By combining theoretical predictions and diamond anvil cell experiments, we found that new materials with different stoichiometries emerge at high pressures. Compounds such as Na₃Cl, Na₂Cl, Na₃Cl₂, NaCl₃, and NaCl₇ are theoretically stable and have unusual bonding and electronic properties. To test this prediction, we synthesized cubic and orthorhombic NaCl₃ and two-dimensional metallic tetragonal Na₃Cl. These experiments establish that compounds violating chemical intuition can be thermodynamically stable even in simple systems at nonambient conditions.
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