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Changes in the bonding of carbon under high pressure leads to unusual crystal chemistry and can dramatically alter the properties of transition metal carbides. In this work, the new orthorhombic polymorph of yttrium carbide, $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Y}}_{4}{\mathrm{C}}_{5}$, was synthesized from yttrium and paraffin oil in a laser-heated diamond anvil cell at $\ensuremath{\sim}50\text{ }\text{ }\mathrm{GPa}$. The structure of $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Y}}_{4}{\mathrm{C}}_{5}$ was solved and refined using in situ synchrotron single-crystal x-ray diffraction. It includes two carbon groups: [${\mathrm{C}}_{2}$] dimers and nonlinear [${\mathrm{C}}_{3}$] trimers. Crystal chemical analysis and density functional theory calculations revealed unusually high noninteger charges (${[{\mathrm{C}}_{2}]}^{5.2\ensuremath{-}}$ and ${[{\mathrm{C}}_{3}]}^{6.8\ensuremath{-}}$) and unique bond orders ($l1.5$). Our results extend the list of possible carbon states at extreme conditions.

Here, we present a method to study the equation of state of opaque amorphous and crystalline materials in diamond anvil cells. The approach is based on measurements of sample dimensions using high-resolution optical microscopy. Data on the volumetric strain as a function of pressure allow deriving the isothermal equation of state of the studied material. The analysis of optical images is fully automatized and allows measuring the sample dimensions with the precision of about 60 nm. The methodology was validated by studying isothermal compression of ω-Ti up to 30 GPa in a Ne pressure transmitting medium. Within the accuracy of the measurements, the bulk modulus of ω-Ti determined using optical microscopy was similar to that obtained from x-ray diffraction. For glassy carbon compressed to ∼30 GPa, the previously unknown bulk modulus was found to be equal to K0 = 28 (2) GPa [K′ = 5.5(5)].

Minerals 11(5), 516 (2021). doi:10.3390/min11050516, We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni$_3$C). It was synthesized in a diamond anvil cell at 184(5) GPa through a direct reaction of a nickel powder with carbon from the diamond anvils upon heating at 3500 (200) K. Ni$_3$C has the cementite-type structure (Pnma space group, a = 4.519(2) Å, b = 5.801(2) Å, c = 4.009(3) Å), which was solved and refined based on in-situ synchrotron single-crystal X-ray diffraction. The pressure-volume data of Ni$_3$C was obtained on decompression at room temperature and fitted to the 3rd order Burch-Murnaghan equation of state with the following parameters: V$_0$ = 147.7(8) Å$^3$, K$_0$ = 157(10) GPa, and K$_0$ ' = 7.8(6). Our results contribute to the understanding of the phase composition and properties of Earth's outer core., Published by MDPI, Basel

Physical review letters 124(21), 216001 (2020). doi:10.1103/PhysRevLett.124.216001, Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal x-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities., Published by APS, College Park, Md.

High pressure Nuclear Magnetic Resonance (NMR) is known to uncover behavior of matter at extreme conditions. However, significant maintenance demands, space requirements and high costs of superconducting magnets render its application unfeasible for regular modern high pressure laboratories. Here, we present a table-top NMR system based on permanent Halbach magnet arrays with dimensions of 25 cm diameter and 4 cm height. At the highest field of 1013 mT, 1H-NMR spectra of Ice VII have been recorded at 25 GPa and ambient temperature. The table-top NMR system can be used together with double sided laser heating set-ups. Feasibility of high-pressure high-temperature NMR was demonstrated by collecting 1H-NMR spectra of H2O at 25 GPa and 1063(50) K. We found that the change in signal intensity in laser-heated NMR diamond anvil cell yields a convenient way for temperature measurements.

This study is devoted to the detailed in situ Raman spectroscopy investigation of propane C3H8 in laser-heated diamond anvil cells in the range of pressures from 3 to 22 GPa and temperatures from 900 to 3000 K. We show that propane, while being exposed to particular thermobaric conditions, could react, leading to the formation of hydrocarbons, both saturated and unsaturated as well as soot. Our results suggest that propane could be a precursor of heavy hydrocarbons and will produce more than just sooty material when subjected to extreme conditions. These results could clarify the issue of the presence of heavy hydrocarbons in the Earth’s upper mantle.

Thermal decomposition of (NH4)2[OsxPt1-xCl6] as single-source precursors for Os–Pt binary alloys has been investigated under ambient and high pressure up to 40 GPa. Thermal decomposition of mixed-metal (NH4)2[OsxPt1-xCl6] precursors in hydrogen atmosphere (reductive environment) under ambient pressure results in formation of β-trans-[Pt(NH3)2Cl2] and α-trans-[Pt(NH3)2Cl2] crystalline intermediates as well as single and two-phase Os–Pt binary alloys. For the first time, direct thermal decomposition of coordination compound under pressure has been investigated. A formation of pure metallic alloys from single-source precursors under pressure has been shown. Miscibility between fcc- and hcp-structured alloys has been probed up to 50 GPa by in situ high-pressure X-ray diffraction. Miscibility gap between fcc- and hcp-structured alloys does not change its positions with pressure up to at least 50 GPa.

Physical review / B 102(16), 165109 (1-8) (2020). doi:10.1103/PhysRevB.102.165109, The atomic and electronic structures of Cu$_2$H and CuH have been investigated by high-pressure nuclear magnetic resonance spectroscopy up to 96 GPa, X-ray diffraction up to 160 GPa, and density functional theory-based calculations. Metallic Cu$_2$H was synthesized at a pressure of 40 GPa, and semimetallic CuH at 90 GPa, found stable up to 160 GPa. For Cu$_2$H, experiments and computations show an anomalous increase in the electronic density of state at the Fermi level for the hydrogen 1s states and the formation of a hydrogen network in the pressure range 43–58 GPa, together with high 1H mobility of ∼10$^{−7}$cm$^2$/s. A comparison of these observations with results on FeH suggests that they could be common features in metal hydrides., Published by Inst., Woodbury, NY

Materialia 14, 100920 (2020). doi:10.1016/j.mtla.2020.100920, Hcp-Ir$_{0.24}$Ru$_{0.36}$Os$_{0.40}$ and fcc-Ir$_{0.84}$Ru$_{0.06}$Os$_{0.10}$ ternary alloys as well as binary hcp-Ir$_{0.33}$Ru$_{0.67}$ and fcc-Ir$_{0.75}$Ru$_{0.25}$ ones were prepared using thermal decomposition of [Ir$_x$Ru$_{1-x}$(NH$_3$)($_5$)Cl][OsyIr$_{(1-y)}$Cl$_6$] single-source precursors in hydrogen flow below 1070 K. These single-phase alloys correspond to ternary and binary peritectic phase diagrams and can be used as synthetic models for rare iridosmine minerals. Thermal decomposition of parent bimetallic precursor [Ir(NH$_3$)($_5$)Cl][OsCl$_6$] has been investigated using in situ powder X-ray diffraction in inert and reductive atmospheres. In reductive atmosphere, [Ir(NH$_3$)($_5$)Cl][OsCl$_6$] forms (NH$_4$)($_2$) [OsCl$_6$] as crystalline intermediate; Ir from its cationic part is reduced by hydrogen with a formation of defect fcc-structured metallic particles; the final product is a metastable hcp-Ir$_{0.5}$Os$_{0.5}$ alloy. In inert atmosphere, the salt decomposes at higher temperature without a formation of any detectable crystalline intermediates; two-phase fcc+hcp mixture forms directly above 800 K. Room temperature compressibility up to 50 GPa has been studied for all prepared alloys in diamond anvil cells. Investigated ternary and binary alloys do not show any phase transitions upon compression at room temperature. In contrast with other investigated ultra-incompressible refractory alloys with osmium and iridium, hcp-Ir$_{0.33}$Ru$_{0.67}$, fcc-Ir$_{0.75}$Ru$_{0.25}$ binary and fcc-Ir$_{0.84}$Ru$_{0.06}$Os$_{0.10}$ ternary alloys show higher compressibility in comparison with pure metals. Fcc-Ir0.75Ru0.25 alloy shows several magnetic phase transitions (at approx. 3.4 K, 135 K and 233 K) that could be related to different magnetic phases., Published by Elsevier, Amsterdam

Minerals 10(6), 542 (2020). doi:10.3390/min10060542, It is widely accepted that the lower mantle consists of mainly three major minerals—ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16–20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg$_{0.76}$Fe$_{0.24}$O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)$_3$O$_4$ phase with CaTi$_2$O$_4$-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone., Published by MDPI, Basel

Angewandte Chemie / International edition 57(29), 9048 - 9053 (2018). doi:10.1002/anie.201805152, A nitrogen‐rich compound, $ReN_{8}·xN_{2}$, was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser‐heated diamond anvil cell. Single‐crystal X‐ray diffraction revealed that the crystal structure, which is based on the ReN8 framework, has rectangular‐shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, $ReN_{8}·xN_{2}$ is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [−N=N−]$_∞$ that constitute the framework have not been previously observed in any compound. Ab initio calculations on $ReN_{8}·xN_{2}$ provide strong support for the experimental results and conclusions., Published by Wiley-VCH, Weinheim

Knowledge of the behavior of hydrogen in metal hydrides is the key for understanding their electronic properties. Here, we present an 1H−NMR study of cubic FeH up to 202 GPa. 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 result, 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., Physical Review X, 9 (3), ISSN:2160-3308

Journal of alloys and compounds 788, 212 - 218 (2019). doi:10.1016/j.jallcom.2019.02.206, Knowledge of the compressional and thermal behaviour of metals and alloys is of a high fundamental and applied value. In this work, we studied the behaviour of Ir, Rh, and their fcc-structured alloys, Ir$_{0.42}$Rh$_{0.58}>$ and Ir$_{0.26}$Os$_{0.05}$Pt$_{0.31}$Rh$_{0.23}$Ru$_{0.15}$, up to 70 GPa using the diamond anvil cell technique with synchrotron X-ray diffraction. We found that all these materials are structurally stable upon room-temperature hydrostatic compression in the whole pressure interval, as well as upon heating to 2273 K both at ambient and high pressure. Rh, Ir$_{0.42}$Rh$_{0.58}$ and Ir$_{0.26}$Os$_{0.05}$Pt$_{0.31}$Rh$_{0.23}$Ru$_{0.15}$ were investigated under static compression for the first time. According to our data, the compressibility of Ir, Rh, fcc–Ir$_{0.42}$Rh$_{0.58}$, and fcc–Ir$_{0.26}$Os$_{0.05}$Pt$_{0.31}$Rh$_{0.23}$Ru$_{0.15}$, can be described with the 3rd order Birch-Murnaghan equation of state with the following parameters: V$_0$ = 14.14(6) Å$^3$·atom$^1 {−1}$, B$_0$ = 341(10) GPa, and B0' = 4.7(3); V$_0$ = 13.73(7) Å$^3$·atom$^{−1}$, B$_0$ = 301(9) GPa, and B$_0$' = 3.1(2); V$_0$ = 13.90(8) Å$^3$·atom$^{−1}$, B$_0$ = 317(17) GPa, and B$_0$' = 6.0(5); V$_0$ = 14.16(9) Å$^3$·atom$^{−1}$, B$_0$ = 300(22) GPa, B$_0$' = 6(1), where V$_0$ is the unit cell volume, B$_0$ and B$_0$' – are the bulk modulus and its pressure derivative., Published by ScienceDirect, Amsterdam [u.a.]

Journal of applied physics 125(9), 095901 (2019). doi:10.1063/1.5067268, Laser heating in a diamond anvil cell (DAC) is a common method for studying material behavior at high-pressure and high-temperature conditions. It has been previously proven that during continuous wave (CW) laser heating of a sample, carbon of the diamond anvils is mobilized, and its diffusion into the sample can lead to undesirable chemical reactions, which, if not detected, may cause misinterpretations of the results of the experiment. Minimizing the heating time with the use of a pulsed laser (PL) is thought to reduce the risk of possible carbon contamination of the sample; however, this has not been proven experimentally. Here, we report the results of our comparative study of the effect of pulsed and continuous wave (CW) laser heating on the mobilization of carbon and its chemical interaction with iron in a diamond anvil cell. Using X-ray absorption near edge structure spectroscopy, Synchrotron Mössbauer Source spectroscopy, and Synchrotron X-ray diffraction, we examined iron samples that were laser heated in DACs in various pressure transmitting media (neon, argon, and potassium chloride). According to our results, the use of the PL heating does not prevent the sample from carbon contamination. A reaction between carbon and iron happens within a few seconds even at moderate temperatures. We found that one analytical technique was generally insufficient to fully characterize the phase composition of the laser-heated samples., Published by American Inst. of Physics, Melville, NY

The diamond anvil cell (DAC) technique is a powerful method for the synthesis and studying of novel materials at extreme conditions. In this work we report on high-pressure high-temperature (HPHT) synthesis of palladium carbides (PdCx) and palladium hydride (PdH) in a laser heated diamond anvil cell. Formation of PdCx with a face-centered cubic (fcc) structure resulted from a chemical reaction of Pd with carbon from the diamond anvils at a pressure of about 50 GPa and temperature of 2500–3000 K. The samples were analyzed in situ using synchrotron X-ray diffraction. The compressional behavior of PdC0.19(3) and PdC0.17(3), was studied on decompression. The fit of the pressure-volume data using the 3rd order Birch-Murnaghan equation of state gave the following parameters: V0 = 65.1 (1) A3, K 0 = 241 (9) GPa and K 0 ’ = 2.1 (3) for PdC0.19(3), and V0 = 64.51 (5) A3, K 0 = 189 (8) GPa and K 0 ’ = 4.5 (4) for PdC0.17(3). The palladium hydride PdH was synthesized at P = 39 (2) GPa and T = 1500 (200) K through a direct reaction of Pd with paraffin oil.

The diamond anvil cell (DAC) technique combined with laser heating is one of the major methods for studying materials at high pressure and high temperature conditions. In this work, we present a transferable double-sided laser heating setup for DACs with in situ temperature determination. The setup allows precise heating of samples inside a DAC at pressures above 200 GPa and could be combined with synchrotron beamline equipment. It can be applied to X-ray diffraction and X-ray transmission microscopy experiments. In the setup, we use high-magnification and low working distance infinity corrected laser focusing objectives that enable us to decrease the size of the laser beam to less than 5 µm and achieve the maximum optical magnification of 320 times. All optical components of the setup were chosen to minimize chromatic and spatial aberrations for accurate in situ temperature determination by multiwavelength spectroscopy in the 570–830 nm spectral range. Flexible design of our setup allows simple interchange of laser sources and focusing optics for application in different types of studies. The setup was successfully tested in house and at the high-pressure diffraction beamline ID15B at the European Synchrotron Radiation Facility. We demonstrate an example of application of the setup for the high pressure–high temperature powder diffraction study of PdH and X-ray transmission microscopy of platinum at 22(1) GPa as a novel method of melting detection in DACs.