Maxim Bykov

University of Cologne | UOC · Department of Chemistry

A novel nitrogen‐rich compound, ReN8·xN2, was synthesized via 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...

Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds...

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K0 = 428(10) GPa), and very hard (nanoindentation hardn...

The synthesis of polynitrogen compounds is of great importance due to their potential as high energy density materials (HEDM), but because of the intrinsic instability of these compounds, their synthesis and stabilization is a fundamental challenge. Polymeric nitrogen units which may be stabilized in compounds with metals at high pressure are now r...

High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN4. A triclinic phase of beryllium tetranitride tr−BeN4 was synthesized from elements at ∼85 GPa. Upon decompression to ambient...

We studied chemical interaction of Sn with H2 by X-ray diffraction methods at pressures of 180-210 GPa. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below Tc = 72 K was obtained; the formation of a high molecular C2/m-SnH14 superhydride and several lower hydrides, fcc SnH2 and C2-Sn12H18,...

We applied single-crystal X-ray diffraction and Raman spectroscopy in a diamond anvil cell up to 36 GPa and first principles theoretical calculations to study the molecular dissociation of solid iodine at high pressure. Unlike previously reported, we find that the familiar Cmce molecular phase transforms to a Cmc21 molecular structure at 16 GPa, an...

We synthesized single and polycrystals of an iron oxide with an unconventional Fe4O5 stoichiometry under high-pressure high-temperature (HP-HT) conditions. The crystals of Fe4O5 adopted a CaFe3O5-type structure composed of linear...

Chemical stability of the alkali halides NaCl and KCl has allowed for their use as inert media in high-pressure high-temperature experiments. Here we demonstrate the unexpected reactivity of the halides with metals (Y, Dy, and Re) and iron oxide (FeO) in a laser-heated diamond anvil cell, thus providing a synthetic route for halogen-containing bina...

Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3...

Tungsten tetraboride has been known so far as a non-stoichiometric compound with a variable composition (e.g. WB4−x, WB4+x). Its mechanical properties could exceed those of hard tungsten carbide, which is widely used nowadays in science and technology. The existence of stoichiometric WB4 has not been proven yet, and its structure and crystal chemis...

Polynitrogen molecules are attractive for high-energy-density materials due to energy stored in nitrogen–nitrogen bonds; however, it remains challenging to find energy-efficient synthetic routes and stabilization mechanisms for these compounds. Direct synthesis from molecular dinitrogen requires overcoming large activation barriers and the reaction...

The high-pressure structural and vibrational properties of a layered transition metal dichalcogenide 2H−NbSe2 were investigated using single-crystal x-ray diffraction and Raman spectroscopy, demonstrating its structural stability up to 35 GPa. The lattice compressibility changes character from being highly anisotropic at low pressures to largely is...

The pressure-induced Mott insulator-to-metal transitions are often accompanied by a collapse of magnetic interactions associated with delocalization of 3d electrons and high-spin to low-spin (HS-LS) state transition. Here, we address a long-standing controversy regarding the high-pressure behavior of an archetypal Mott insulator FeBO3 and show the...

The metal-insulator transition driven by electronic correlations is one of the most fundamental concepts in condensed matter. In mixed-valence compounds, this transition is often accompanied by charge ordering (CO), resulting in the emergence of complex phases and unusual behaviors. The famous example is the archetypal mixed-valence mineral magneti...

Magnetic order is frustrated on the orthorhombic lattice of van der Waals layered FeOCl. Antiferromagnetic (AFM) order is attained at ambient pressure upon cooling through TN=81 K, due to an accompanying monoclinic lattice distortion lifting the magnetic frustration. Within the paramagnetic state at 293 K, an incommensurate structural modulation ap...

Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions1,2. Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials anal...

The success of high-pressure research relies on the inventive design of pressure-generating instruments and materials used for their construction. In this study, the anvils of conical frustum or disk shapes with flat or modified culet profiles (toroidal or beveled) were prepared by milling an Ia-type diamond plate made of a (100)-oriented single cr...

Charged molecular species, such as [N2]x–, [O2]x–, [C2]x–, and [S2]x–, follow the paradigm of carrying integer values of electrons. Here, the Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3 compounds were produced and characterized <70 GPa and evidenced to be composed of paradigm-breaking [N2]x– dimers with noninteger charges of −0.75, −1.5, −1.5, and −0...

Understanding of recently reported putative close-to-room-temperature superconductivity in C–S–H compounds at 267 GPa demands a reproducible synthesis protocol as well as knowledge of the compounds' structure and composition. We synthesized C–S–H compounds with various carbon compositions at high pressures from elemental carbon C and methane CH4, s...

Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions. Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials analysi...

Single-crystal synchrotron x-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of the high-pressure (HP) phase of molecular methane above 20 GPa up to 71 GPa at room temperature. The structure of the HP phase is trigonal R3, which can be represented as a distortion of the cubic phase B,...

The high-pressure synthesis of rhenium nitride pernitride with a crystal structure that is unusual for transition metal dinitrides and high values of hardness and bulk modulus attracted significant attention to this system. We investigate the thermodynamic and electronic properties of the P21/c phase of ReN2 and compare them with two other polytype...

Single-crystal synchrotron X-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of the high-pressure (HP) phase of molecular methane above 20 GPa up to 71 GPa. The structure of HP phase is trigonal R3, which can be represented as a distortion of the cubic phase B, previously documented at...

Understanding of recently reported putative close-to-room-temperature superconductivity in C-S-H compounds at 267 GPa demands reproducible synthesis protocol as well as knowledge of its structure and composition. We synthesized C-S-H compounds with various carbon composition at high pressures from elemental C and methane CH4, sulfur S, and molecula...

High pressure synthesis of rhenium nitride pernitride ReN$_2$ with crystal structure unusual for transition metal dinitrides and high values of hardness and bulk modulus attracted significant attention to this system. We investigate the thermodynamic and electronic properties of the P2$_1$/c phase of ReN$_2$ and compare them with two other polytype...

Most of the studied two-dimensional (2D) materials are based on highly symmetric hexagonal structural motifs. In contrast, lower-symmetry structures may have exciting anisotropic properties leading to various applications in nanoelectronics. In this work we report the synthesis of nickel diazenide NiN2 which possesses atomic-thick layers comprised...

The Front Cover shows a possible deep oxygen cycle in early Earth. FeOOH (“rust”), produced by anoxygenic photosynthesis and accumulated on the ocean floor, was transferred to the lower mantle by subducting slabs. At high pressures and temperatures, FeOOH decomposes into a mixture of complex iron oxides, water, and oxygen. Oxidizing fluids rising t...

Goethite, α‐FeOOH, is a major phase among oxidized iron species, commonly called rust. We studied the behavior of iron (III) oxyhydroxide up to 81 GPa and 2100 K using in situ synchrotron single‐crystal X‐ray diffraction. At high pressure‐temperature conditions FeOOH decomposes forming oxygen‐rich fluid and different mixed valence iron oxides (prev...

Nitrogen and water are very abundant in nature; however, the way they chemically react at extreme pressure–temperature conditions is unknown. Below 6 GPa, they have been reported to form clathrate compounds. Here, we present Raman spectroscopy and x-ray diffraction studies in the H2O–N2 system at high pressures up to 140 GPa. We find that clathrate...

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(...

The high-precision X-ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X-ray Free-Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X-...

Synthesis and characterization of nitrogen-rich materials is important for the design of novel high energy density materials due to extremely energetic low-order nitrogen–nitrogen bonds. The balance between the energy output and stability may be achieved if polynitrogen units are stabilized by resonance as in cyclo-N5− pentazolate salts. Here we de...

We synthesized two C-S-H compounds from a mixture of carbon and sulfur in hydrogen—C:(H2S)2H2 and from sulfur in mixed methane-hydrogen fluids—(CH4)x(H2S)(2−x)H2 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...

The ultrafast synthesis of ε-Fe3N1+x in a diamond-anvil cell (DAC) from Fe and N2 under pressure was observed using serial exposures of an X-ray free electron laser (XFEL). When the sample at 5 GPa was irradiated by a pulse train separated by 443 ns, the estimated sample temperature at the delay time was above 1400 K, confirmed by in situ transform...

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...

Alkaline earth metal peroxides are typical examples of ionic compounds containing polyanions. We herein report a stable BaO2 phase at high pressure up to 130 GPa found via a first-principles computational structure search and high-pressure experimental investigations. The identified monoclinic structure (space group C2/m) can be derived by sublatti...

Direct reaction between nitrogen and tantalum at approximately 100 GPa results in the energetic nitrogen‐rich compounds TaN4 and TaN5, which feature N4 chains and unprecedented branched single‐bonded polymeric nitrogen chains in the crystal structures, respectively. TaN5 possesses an extraordinary volumetric energy density of 18 kJ cm⁻³, exceeding...

The structure and properties of metal-hydrides at extreme conditions is key to the understanding of hydrogen-storage technologies, high-temperature superconductivity, and the dynamics of planetary cores. Here we investigate the phase relations and magnetic properties of iron hydrides, including two novel FeH x compounds, up to 63 GPa and 1800 K by...

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 t...

A structure and equation of the state of δ-AlOOH has been studied at room temperature, up to 29.35 GPa, by means of single crystal X-ray diffraction in a diamond anvil cell using synchrotron radiation. Above ~10 GPa, we observed a phase transition with symmetry changes from P21nm to Pnnm. Pressure-volume data were fitted with the second order Birch...

High pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. However, the application of pressure is counterintuitive for the synthesis of layered van der Waals bonded compounds, and consequently, in a search for novel two-dimensional materials. Here we report the synthesis at ~90 GPa...

Polynitrogen molecules represent the ultimate high energy-density materials as they have a huge potential chemical energy originating from their high enthalpy. However, synthesis and storage of such compounds remain a big challenge because of difficulties to find energy efficient synthetic routes and stabilization mechanisms. Compounds of metals wi...

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. F...

Hcp–Ir0.24Ru0.36Os0.40 and fcc–Ir0.84Ru0.06Os0.10 ternary alloys as well as binary hcp–Ir0.33Ru0.67 and fcc–Ir0.75Ru0.25 ones were prepared using thermal decomposition of [IrxRu1-x(NH3)5Cl][OsyIr(1-y)Сl6] single-source precursors in hydrogen flow below 1070 K. These single-phase alloys correspond to ternary and binary peritectic phase diagrams and...

With the exception of lithium, alkali metals do not react with elemental nitrogen either at ambient conditions or at elevated temperatures, requiring the search for alternative synthetic routes to their nitrogen-containing compounds. Here using a controlled decomposition of sodium azide (NaN3) at high pressure conditions, we synthesize two novel co...

X-ray synchrotron diffraction (XRD) measurements of single-crystal and powder molybdenum disulfide MoS2 are performed at pressures (P) up to 78 GPa and temperatures (T) of 20 to 298 K in diamond-anvil cells. The results on single crystals demonstrate a sharp pressure induced isosymmetric phase transition of 2Hc to 2Ha modification at 23 GPa at 40 a...

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 hi...

Feldspars are rock-forming minerals that make up most of the Earth’s crust. Along the mantle geotherm, feldspars are stable at pressures up to 3 GPa and may persist metastably at higher pressures under cold conditions. Previous structural studies of feldspars are limited to ~10 GPa, and have shown that the dominant mechanism of pressure-induced def...

The crystal structure of MgCO 3 -II has long been discussed in the literature where DFT-based model calculations predict a pressure-induced transition of the carbon atom from the sp² to the sp³ type of bonding. We have now determined the crystal structure of iron-bearing MgCO 3 -II based on single-crystal X-ray diffraction measurements using synchr...

Laser heating of rhenium in a diamond anvil cell to 3000±300 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 shortest C–C distances [1.758(3) Å at 219(5) GPa and 1.850(4) Å at 180(7) GPa] found in honeycomb‐like carbon nets in the s...

Metal–inorganic frameworks Hf4N20⋅N2, WN8⋅N2 and Os5N28⋅N2 built of transition metals and polymeric nitrogen linkers were synthesized by M. Bykov et al. in a one‐step synthesis from elements at high‐pressure conditions (DOI: 10.1002/anie.202002487). The channel‐type pores are filled with ordered one‐dimensional arrays of nitrogen molecules. Due to...

Metall‐anorganische Gerüstverbindungen Hf4N20⋅N2, WN8⋅N2 und Os5N28⋅N2, die aus Übergangsmetallen und polymeren Stickstofflinkern aufgebaut sind, wurden von M. Bykov et al. in einer einstufigen Synthese aus den Elementen unter Hochdruckbedingungen hergestellt (DOI: 10.1002/ange.202002487). Die kanalartigen Poren sind mit eindimensionalen Anordnunge...

The synthesis of various polynitrogen compounds have been actively pursued for the past hundred years due to their potential as high energy density materials. Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Here we report one-step synthesis of metal-inorganic frameworks Hf4N...

A one‐step high‐pressure synthetic route is used to complex metal–inorganicframeworks built of transition metals(Hf, Os, and W) that are connected via polymeric nitrogen linkers. The pores are filled with ordered one‐dimensional arrays of nitrogen molecules. Owing to the conjugated π‐systems, these inorganic polymers are conductive materials. Abst...

Three binary fcc-structured alloys (fcc–Ir0.50Pt0.50, fcc–Rh0.66Pt0.33 and fcc–Rh0.50Pd0.50) were prepared from [Ir(NH3)5Cl][PtCl6], [Ir(NH3)5Cl][PtBr6], [Rh(NH3)5Cl]2[PtCl6]Cl2 and [Rh(NH3)5Cl][PdCl4]·H2O, respectively, as single-source precursors. All alloys were prepared by thermal decomposition in gaseous hydrogen flow below 800 °C. Fcc–Ir0.50P...

Ein gemischtvalentes Eisenoxid mit ungewöhnlicher Fe5O6‐Stöchiometrie wurde synthetisiert, wie S. V. Ovsyannikov et al. in ihrer Zuschrift (DOI: 10.1002/ange.201914988) beschreiben. Nahe 275 K durchläuft das Material einen Ladungsordnungsübergang des Verwey‐Typs, der einhergeht mit einer Dimerisierung in den Eisenketten und der Bildung neuer Fe‐Fe‐...

A novel mixed‐valent iron oxide with an unconventional Fe5O6 stoichiometry was synthesized by S. V. Ovsyannikov et al., as reported in their Communication (DOI: 10.1002/anie.201914988). Near 275 K, the material undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and the formation of new Fe−Fe...

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...

Functional oxides whose physicochemical properties may be reversibly changed at normal conditions are perspective candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in s...

Functional oxides whose physicochemical properties may be reversibly changed at normal conditions are perspective candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in s...