arXiv subjects

Konstantin Glazyrin

Publications and source records attributed to Konstantin Glazyrin.

32 records · Page 2Linked to original sources

arXiv2021

Fe0.79Si0.07B0.14 metallic glass gaskets for high-pressure research beyond 1 Mbar

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for x-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe0.79Si0.07B0.14 in a number of high-pressure x-ray diffraction (XRD) experiments in DACs equipped with conventional and toroidal-shape diamond anvils. The experiments were conducted in either uniaxial or radial geometry with x-ray beams of micron to sub-micron size. We report that the Fe0.79Si0.07B0.14 metallic glass gaskets offered stable sample environment under compression exceeding one megabar in all XRD experiments described here, even in those involving inter- or small-molecule gases (e.g. Ne, H2) used as pressure transmitting media or in those with laser heating in a DAC. These emphasize the material's importance for a great number of delicate experiments conducted under extreme conditions. Our results indicate that the application of Fe0.79Si0.07B0.14 metallic glass gaskets in XRD experiments of both uniaxial and radial geometries substantially improves the signal-to-noise ratio in comparison to that with conventional gaskets made of Re, W, steel or other crystalline metals.

cond-mat.mtrl-sci↗

arXiv2021

High-Pressure Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3 Featuring Nitrogen Dimers with Non-Integer Charges and Anion-Driven Metallicity

Charged nitrogen dimers are ubiquitous in high-pressure binary metal-nitrogen systems. They are known to possess integer formal charges x varying from one through four. Here, we present the investigation of the binary alkali- and alkaline earth metal-nitrogen systems, Na-N, Ca-N, Sr-N, Ba-N to 70 GPa. We report on compounds-Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3-featuring charged nitrogen dimers with paradigm-breaking non-integer charges, x = 0.67, 0.75 and 1.5. The metallic nature of all four compounds is deduced from ab initio calculations. The conduction electrons occupy the pi* antibonding orbitals of the charged nitrogen dimers that results in anion-driven metallicity. Delocalization of these electrons over the pi* antibonding states enables the non-integer electron count of the dinitrogen species. Anion-driven metallicity is expected to be found among a variety of compounds with homoatomic anions (e.g., polynitrides, carbides, and oxides), with the conduction electrons playing a decisive role in their properties.

cond-mat.mtrl-sci↗

arXiv2021

High-pressure synthesis of Dirac materials: layered van der Waals bonded BeN$_4$ polymorph

High pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here we report the synthesis at ~90 GPa of novel beryllium polynitrides, monoclinic and triclinic BeN4. The triclinic phase, upon decompression to ambient conditions, transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds consisting of polyacetylene-like nitrogen chains with conjugated π-systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN4 layer, i.e. beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions.

cond-mat.mtrl-sci↗

arXiv2020

Structure and composition of C-S-H compounds up to 143 GPa

We synthesized two C-S-H compounds from a mixture of carbon and sulfur in hydrogen and from sulfur in mixed methane-hydrogen fluids at 4 GPa. X-ray synchrotron single-crystal diffraction and Raman spectroscopy have been applied to these samples up to 58 and 143 GPa, respectively. Both samples show a similar Al2Cu type I4/mcm basic symmetry, while the hydrogen subsystem evolves with pressure via variously ordered molecular and extended modifications. The methane bearing sample lowers symmetry to an orthorhombic Pnma structure after laser heating to 1400 K at 143 GPa. The results suggest that superconducting C-S-H compounds are structurally different from a common Im-3m H3S.

cond-mat.supr-con↗

arXiv2020

Synthesis and Compression study of orthorhombic $Fe_7(C,Si)_3$: A possible constituent of the Earth's core

The orthorhombic phase of Si-doped Fe carbide is synthesized at high pressures and temperatures using laser-heated diamond anvil cell (LHDAC), followed by its characterization using X-ray diffraction (XRD) measurements, Transmission Electron Microscopy (TEM), and Raman spectroscopy. High-pressure XRD measurements are carried out up to about 104 GPa at room temperature for determination of the equation of state (EOS) parameters of the synthesized sample. No evidence of structural transition is observed, though two anomalies are found in the compression behaviour of our sample at about 28 and 78 GPa, respectively. Pressure evolution of isothermal bulk modulus shows elastic stiffening around 28 GPa followed by softening around 78 GPa. These anomalies are possibly related to two different magnetic transitions driven by pressure-induced anisotropic strain in the unit cell. Extrapolation of the density profile of our study to the inner core conditions agrees very well with PREM data with an uncertainty of about 3-4%. We have estimate bulk modulus value seems to be 8-9% less than that of PREM data in the shown pressure range and is best matched in comparison to other reported values for the non-magnetic phase.

cond-mat.mtrl-sci↗

arXiv2020

Novel hydrogen clathrate hydrate

We report a new hydrogen clathrate hydrate synthesized at 1.2 GPa and 298 K documented by single-crystal X-ray diffraction, Raman spectroscopy, and first-principles calculations. The oxygen sublattice of the new clathrate hydrate matches that of ice II, while hydrogen molecules are in the ring cavities, which results in the trigonal R3c or R-3c space group (proton ordered or disordered, respectively) and the composition of (H2O)6H2. Raman spectroscopy and theoretical calculations reveal a hydrogen disordered nature of the new phase C1', distinct from the well-known ordered C1 clathrate, to which this new structure transforms upon compression and/or cooling. This new clathrate phase can be viewed as a realization of a disordered ice II, unobserved before, in contrast to all other ordered ice structures.

cond-mat.mtrl-sci↗

arXiv2020

Pressure induced lattice expansion and phonon softening in layered $ReS_2$

We report high pressure X-ray diffraction and a detailed systematic Raman measurements on $ReS_2$ sample, which is mechanically exfoliated from a single crystal. A few new Bragg peaks are observed to emerge above 6 GPa indicating a structural transition from distorted $1T$ to distorted $1T$$^{\prime}$ in triclinic structure. The same is corroborated by appearance of new Raman modes in the same pressure range. Softening of the Raman modes corresponding to $Re$ atom vibrations are observed in the distorted $1T$$^{\prime}$ phase in the pressure range 15-25 GPa. In the same pressure range the anomalous change in the volume is found to be induced by the lattice expansion. The volume expansion is related to the sliding of layers leading to octahedral distortion and increase in octahedral volume. The sample is found to be much incompressible above 25 GPa with respect to below 15 GPa data. The same is also reflected in the Raman mode shifts with pressure.

cond-mat.mtrl-sci↗

arXiv2020

Metallic Hydrogen Sublattice and Proton Mobility in Copper Hydride at High Pressure

Atomic and electronic structures of Cu2H and CuH have been investigated by high pressure NMR spectroscopy, X-ray diffraction and ab-initio calculations. Metallic Cu2H was synthesized at a pressure of 40 GPa, and semi-metallic CuH at 90 GPa, found stable up to 160 GPa. Experiments and computations suggest the formation of a metallic 1H-sublattice as well as a high 1H mobility of ~10-7 cm2/s in Cu2H. Comparison of Cu2H and FeH data suggests that deviations from Fermi gas behavior, formation of conductive hydrogen networks, and high 1H mobility could be common features of metal hydrides.

cond-mat.mtrl-sci↗

arXiv2020

Novel rhenium carbides at 200 GPa

Laser heating of rhenium in a diamond anvil cell to 3000 K at about 200 GPa results in formation of two previously unknown rhenium carbides, hexagonal WC-type structured ReC and orthorhombic TiSi2-type structured ReC2. The Re-C slid solution formed at multimegabar pressure has the carbon content of ca. 20 at%. Unexpectedly long C-C distances (ca. 1.76-1.85 A) in 'graphene-like' carbon nets in the structure of ReC2 cannot be explained by a simple covalent bonding between carbon atoms and suggest that at very high pressures the mechanism of interaction between carbon atoms in inorganic compounds may be different from that considered so far.

cond-mat.mtrl-sci↗

arXiv2019

Revisiting spin state crossover in (MgFe)O by means of high resolution X-ray diffraction from a single crystal

(MgFe)O is a solid solution with ferrous iron undergoing the high to low spin state (HS-LS) crossover under high pressure. The exact state of the material in the region of the crossover is still a mystery, as domains with different spin states may coexist over a wide pressure range without changing the crystal structure neither from the symmetry nor from the atomic positions point of view. At the conditions of the crossover, (MgFe)O is a special type of microscopic disorder system. We explore the influences of (a) stress-strain relations in a diamond anvil cell, (b) time relaxation processes, and (c) the crossover itself on the characteristic features of a single crystal (111) Bragg spot before, during and after the transformation. Using high resolution X-ray diffraction as a novel method for studies of unconventional processes at the conditions of suppressed diffusion, we detect and discuss subtle changes of the (111) Bragg spot projections which we measure and analyze as a function of pressure. We report changes of the spot shape which can be correlated with the HS-LS relative abundance. In addition, we report the formation of structural defects as an intrinsic material response. These static defects are accumulated during transformation of the material from HS to LS.

cond-mat.mtrl-sci↗

arXiv2019

B1-B2 phase transition in MgO at ultra-high static pressure

Studies of the behaviour of solids at ultra-high pressures, those beyond 200 GPa, contribute to our fundamental understanding of materials properties and allow an insight into the processes happening at such extreme conditions relevant for terrestrial and extra-terrestrial bodies. The behaviour of magnesium oxide, MgO, is of a particular importance, as it is believed to be a major phase in the Earth lower mantle and the interior of super-Earth planets. Here we report the results of studies of MgO at ultra-high static pressures up to ca. 660 GPa using the double-stage diamond anvil cell technique with synchrotron X-ray diffraction. We observed the B1-B2 phase transition in the pressure interval from 429(10) GPa to 562(10) GPa setting an unambiguous reference mark for the B1-B2 transition in MgO at room temperature. Our observations allow constraining theoretical predictions and results of available so far dynamic compression experiments.

cond-mat.mtrl-sci↗

arXiv2019

Pressure induced Hydrogen-Hydrogen interaction in metallic FeH revealed by NMR

Knowledge of the behavior of hydrogen in metal hydrides is the key for understanding their electronic properties. So far, no experimental methods exist to access these properties beyond 100 GPa, where high-Tc superconductivity emerges. Here, we present an 1H-NMR study of cubic FeH up to 200GPa. We observe a distinct deviation from the ideal metallic behavior between 64 and 110 GPa that suggests pressure-induced H-H interactions. Accompanying ab-initio calculations support this interpretation, as they reveal the formation of an intercalating sublattice of electron density, which enhances the hydrogen contribution to the electronic density of states at the Fermi level. This study shows that pressure induced H-H interactions can occur in metal hydrides at much lower compression and larger H-H distances than previously thought and stimulates an alternative pathway in the search for novel high-temperature superconductors.

cond-mat.mtrl-sci↗

arXiv2017

First non-icosahedral boron allotrope synthesized at high pressure and high temperature

Theoretical predictions of pressure-induced phase transformations often become long-standing enigmas because of limitations of contemporary available experimental possibilities. Hitherto the existence of a non-icosahedral boron allotrope has been one of them. Here we report on the first non-icosahedral boron allotrope, which we denoted as ζ-B, with the orthorhombic α-Ga-type structure (space group Cmce) synthesized in a diamond anvil cell at extreme high-pressure high-temperature conditions (115 GPa and 2100 K). The structure of ζ-B was solved using single-crystal synchrotron X-ray diffraction and its compressional behavior was studied in the range of very high pressures (115 GPa to 135 GPa). Experimental validation of theoretical predictions reveals the degree of our up-to-date comprehension of condensed matter and promotes further development of the solid state physics and chemistry.

cond-mat.mtrl-sci↗

arXiv2011

Detection of melting by in-situ observation of spherical-drop formation in laser-heated diamond-anvil cells

A simple method for detection of melting event in laser-heated diamond anvil cells (DACs) is introduced. The melting is registered optically by the formation of spherical drops of the investigated material as heated in an inert pressure transmitting medium. Feasibility of the method is demonstrated on the examples of metal (iron and gold) and iron oxide (Fe2O3), materials molten at pressures over 40 GPa employing a portable laser heating system.

cond-mat.mtrl-sci↗