Novel Superhard Boron Nitrides, BN and BN: Crystal Chemistry and First-Principles Studies.

Tetragonal and hexagonal hybrid sp/sp carbon allotropes C were proposed based on crystal chemistry and subsequently used as template structures to identify new binary phases of the B-N system, specifically tetragonal and hexagonal boron nitrides, BN and BN. The ground structures and energy-dependent quantities of the new phases were computed within the framework of quantum density functional theory (DFT). All four new boron nitrides were found to be cohesive and mechanically (elastic constants) stable.

High-Pressure Synthesis of Cubic ZnO and Its Solid Solutions with MgO Doped with Li, Na, and K.

The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgZnO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction.

Local structure, thermodynamics, and melting of boron phosphide at high pressures by deep learning-driven ab initio simulations.

Boron phosphide (BP) is a (super)hard semiconductor constituted of light elements, which is promising for high demand applications at extreme conditions. The behavior of BP at high temperatures and pressures is of special interest but is also poorly understood because both experimental and conventional ab initio methods are restricted to studying refractory covalent materials. The use of machine learning interatomic potentials is a revolutionary trend that gives a unique opportunity for high-temperature study of materials with ab initio accuracy.

Prediction of Novel Ultrahard Phases in the B-C-N System from First Principles: Progress and Problems.

The modern synthesis of superhard and, especially, ultrahard phases is a fascinating area of research that could lead to the design of new, industrially important materials. Computational methods built within the well-established quantum mechanics framework of density functional theory (DFT) play an important role in the search for these advanced materials and the prediction of their properties. The close relationship between the physical properties of carbon and boron nitride has led to particular interest in the B-C-N ternary system, characterized by the small radii of the elements, resulting in short interatomic distances and reduced volumes-the parameters being 'recipes' for very high hardness in three-dimensional structures.

Computational prediction of new magnetic materials.

The discovery of new magnetic materials is a big challenge in the field of modern materials science. We report the development of a new extension of the evolutionary algorithm USPEX, enabling the search for half-metals (materials that are metallic only in one spin channel) and hard magnetic materials. First, we enabled the simultaneous optimization of stoichiometries, crystal structures, and magnetic structures of stable phases.

Discovery of new boron-rich chalcogenides: orthorhombic BX (X=S, Se).

New boron-rich sulfide BS and selenide BSe have been discovered by combination of high pressure - high temperature synthesis and ab initio evolutionary crystal structure prediction, and studied by synchrotron X-ray diffraction and Raman spectroscopy at ambient conditions. As it follows from Rietveld refinement of powder X-ray diffraction data, both chalcogenides have orthorhombic symmetry and belong to Pmna space group. All experimentally observed Raman bands have been attributed to the theoretically calculated phonon modes, and the mode assignment has been performed.

High-Pressure Design of Advanced BN-Based Materials.

The aim of the present review is to highlight the state of the art in high-pressure design of new advanced materials based on boron nitride. Recent experimental achievements on the governing phase transformation, nanostructuring and chemical synthesis in the systems containing boron nitride at high pressures and high temperatures are presented. All these developments allowed discovering new materials, e.

Ultra-fast mechanochemical synthesis of boron phosphides, BP and B12P2.

Here we propose a new approach to the synthesis of single-phase boron phosphides (BP and B12P2) by mechanochemical reactions between boron phosphate and magnesium/magnesium diboride in the presence of an inert diluent (sodium chloride). The proposed method is characterized by the simplicity of implementation, high efficiency, low cost of the product, and good perspectives for large-scale production.

A novel phase of beryllium fluoride at high pressure.

A previously unknown thermodynamically stable high-pressure phase of BeF2 has been predicted using the evolutionary algorithm USPEX. This phase occurs in the pressure range 18-27 GPa. Its structure has C2/c space group symmetry and contains 18 atoms in the primitive unit cell.

Equilibrium p-T phase diagram of boron: experimental study and thermodynamic analysis.

Solid-state phase transformations and melting of high-purity crystalline boron have been in situ and ex situ studied at pressures to 20 GPa in the 1500-2500 K temperature range where diffusion processes become fast and lead to formation of thermodynamically stable phases. The equilibrium phase diagram of boron has been constructed based on thermodynamic analysis of experimental and literature data. The high-temperature part of the diagram contains p-T domains of thermodynamic stability of rhombohedral β-B106, orthorhombic γ-B28, pseudo-cubic (tetragonal) t'-B52, and liquid boron (L).

Creation of nanostuctures by extreme conditions: high-pressure synthesis of ultrahard nanocrystalline cubic boron nitride.

The synthesis of high-purity bulk nanostructured cubic boron nitride (cBN) at 20 GPa and 1770 K by direct phase transformation of graphite-like BN with an "ideal random layer" structure is reported. The two-times increase of hardness of nano-cBN (H(V) = 85 GPa) with respect to conventional polycrystalline cBN (H(V) ∼ 45 GPa) is evidently a result of nanosize effects.

Kinetics of the wurtzite-to-rock-salt phase transformation in ZnO at high pressure.

Kinetics of the wurtzite-to-rock-salt transformation in ZnO has been studied in the 5-7 GPa pressure range at temperatures below the activation of diffusion processes. The detailed analysis of non-isothermal experimental data using the general evolution equation describing the kinetics of direct phase transformations in solids allowed us to study the kinetic particularities of both nucleation and growth of the rock-salt phase in parent wurtzite ZnO. The main rate-limiting processes are thermally activated nucleation (E(N) = 383 kJ mol(-1) at 6.

Phase diagram of the B-BN system at 5 GPa.

The chemical interaction and phase relations in the B-BN system have been in situ studied at 5 GPa and temperatures up to 2800 K using X-ray diffraction with synchrotron radiation. The thermodynamic analysis of the B-BN system based on experimental data allowed us to construct equilibrium and metastable phase diagrams of the system at 5 GPa. The only thermodynamically stable boron subnitride, B(13)N(2), melts incongruently at 2600 K and forms eutectic equilibrium with boron at 2300 K and 4 at.

Portable multi-anvil device for in situ angle-dispersive synchrotron diffraction measurements at high pressure and temperature.

A recently developed portable multi-anvil device for in situ angle-dispersive synchrotron diffraction studies at pressures up to 25 GPa and temperatures up to 2000 K is described. The system consists of a 450 ton V7 Paris-Edinburgh press combined with a Stony Brook ;T-cup' multi-anvil stage. Technical developments of the various modifications that were made to the initial device in order to adapt the latter to angular-dispersive X-ray diffraction experiments are fully described, followed by a presentation of some results obtained for various systems, which demonstrate the power of this technique and its potential for crystallographic studies.

Ultimate metastable solubility of boron in diamond: synthesis of superhard diamondlike BC5.

Here, we report the synthesis of cubic BC5 (c-BC5), the diamondlike B-C phase with the highest boron content ever achieved, at 24 GPa and about 2200 K, using both a laser-heated diamond anvil cell and large-volume multianvil apparatus. The synthesized phase is low compressible (bulk modulus of 335 GPa), conductive, and exhibits extreme Vickers hardness (71 GPa), unusually high for superhard materials fracture toughness (9.5 MPa m;{0.

Ionic high-pressure form of elemental boron.

Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new 'element' turned out to be a compound containing less than 60-70% of boron, and it was not until 1909 that 99% pure boron was obtained. And although we now know of at least 16 polymorphs, the stable phase of boron is not yet experimentally established even at ambient conditions.

Phase diagram of the B-B2O3 system at 5 GPa: experimental and theoretical studies.

X-ray diffraction with synchrotron radiation has been used to study in situ the chemical interaction of beta-rhombohedral boron with boron (III) oxide and phase relations in the B-B2O3 system at pressures up to 6 GPa in the temperature range from 300 to 2800 K. The B-B2O3 system has been thermodynamically analyzed, and its equilibrium phase diagram at 5 GPa has been constructed. Only one thermodynamically stable boron suboxide, B6O, exists in the system.

Comment on "Synthesis of ultra-incompressible superhard rhenium diboride at ambient pressure".

Chung et al. (Reports, 20 April 2007, p. 436) reported the synthesis of superhard rhenium diboride (ReB2) at ambient pressure.

Rhombohedral boron subnitride, B13N2, by X-ray powder diffraction.

The structure of the title compound consists of distorted B12 icosahedra linked by N-B-N chains. The compound crystallizes in the rhombohedral space group R3m (No. 166).

Reversible pressure-induced structure changes in turbostratic BN-C solid solutions.

The results obtained by Rietveld analysis and numerical modeling of B-C-N layered clusters with various types of lattice defects explain the evolution of diffraction patterns of turbostratic graphite-like BN-C solid solutions which are experimentally observed at room temperature at pressures up to 30 GPa. Above 20 GPa a reversible diffusionless transformation of the initial turbostratic structure takes place, giving a high-pressure phase formed by close-packed buckled layers having a diamond-like structure.

Identification of the diamond-like B-C phase by confocal Raman spectroscopy.

The new diamond-like B-C phase was obtained from the graphite-like BC phase in a laser-heated diamond anvil cell at high temperature 2230+/-140 K and high pressure 45 GPa. Raman spectra of the new phase measured at ambient conditions revealed a peak at 1315 cm(-1), which was attributed to longitudinal-optical (LO) mode. The X-Y Raman mapping was used to investigate spatial distribution of the diamond-like phases and was shown to be a powerful tool in studying the sp(2)-to-sp(3) phase transformations occurring in the diamond cell under high temperature and high pressure.