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High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the Zn-N system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: β-Zn3N2, α-ZnN4, and β-ZnN4, formed at 35.0, 63.5, and 81.7 GPa, respectively. Whereas β-Zn3N2 contains the N3- nitride, both ZnN4 solids are found to be composed of polyacetylene-like [N4]∞2- chains. Upon the decompression of β-ZnN4 below 72.7 GPa, a first-order displacive phase transition is observed from β-ZnN4 to α-ZnN4. The α-ZnN4 phase is detected down to 11.0 GPa, at lower pressures decomposing into the known α-Zn3N2 (space group Ia3) and N2. The equations of states of β-ZnN4 and α-ZnN4 are also determined, and their bulk moduli are found to be K0 = 126(9) GPa and K0 = 76(12) GPa, respectively. Density functional theory calculations were also performed and provide further insight into the Zn-N system. Moreover, comparing the Mg-N and Zn-N systems underlines the importance of minute chemical differences between metal cations in the resulting synthesized phases.

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)].

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe2O3 and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites. © 2021 American Physical Society. We acknowledge the Deutsches Elektronen-Synchrotron (DESY, PETRA III), the European Synchrotron Radiation Facility (ESRF), and the Advance Photon Source (APS) for provision of beamtime. N. D. and L. D. thank the Federal Ministry of Education and Research, Germany (BMBF, Grant No. 05K19WC1) and the Deutsche Forschungsgemeinschaft (DFG Projects No. DU 954–11/1, No. DU 393–9/2, and No. DU 393–13/1) for financial support. N. D. and I. A. A. thank the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971). Electronic structure calculations were supported by the Russian Science Foundation (Project No. 18-12-00492). Theoretical analysis of chemical bonding was supported by the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISIS” (No. K2-2019-001) implemented by a governmental decree, No. 211. Support from the Knut and Alice Wallenberg Foundation (Wallenberg Scholar Grant No. KAW-2018.0194), the Swedish Government Strategic Research Areas and SeRC, and the Swedish Research Council (VR) Grant No. 2019-05600 is gratefully acknowledged.

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.

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

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.