arXiv subjects

Vladimir L. Solozhenko

Publications and source records attributed to Vladimir L. Solozhenko.

At least 55 records · Page 3Linked to original sources

arXiv2015

Boron phosphide under pressure: in situ study by Raman scattering and X-ray diffraction

Cubic boron phosphide BP has been studied in situ by X-ray diffraction and Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk modulus of B0 = 174(2) GPa has been established, which is in excellent agreement with our ab initio calculations. The data on Raman shift as a function of pressure, combined with equation-of-state data, allowed us to estimate the Grüneisen parameters of the TO and LO modes of zinc-blende structure, γGTO = 1.16 and γGLO = 1.04, just like in the case of other AIIIBV diamond-like phases, for which γGTO > γGLO = 1. We also established that the pressure dependence of the effective electro-optical constant α is responsible for a strong change in relative intensities of the TO and LO modes from ITO/ILO ~0.25 at 0.1 MPa to ITO/ILO ~2.5 at 45 GPa, for which we also find excellent agreement between experiment and theory.

cond-mat.mtrl-sci↗

arXiv2015

Phonon study of rhombohedral BS under high pressure

Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under pressures up to 34 GPa at room temperature. No pressure-induced structural phase transition was observed, while strong pressure shift of Raman bands towards higher wavenumbers has been revealed. IR spectroscopy as a complementary technique has been used in order to completely describe the phonon modes of r-BS. All experimentally observed bands have been compared with theoretically calculated ones and modes assignment has been performed. r-BS enriched by 10B isotope was synthesized, and the effect of boron isotopic substitution on Raman spectra was observed and analyzed.

cond-mat.mtrl-sci↗

arXiv2014

Thermodynamic calculation of the B-C system at pressures to 24 GPa

The evolution of topology of the B-C phase diagram has been studied at pressures up to 24 GPa using models of phenomenological thermodynamics with interaction parameters derived from experimental data on phase equilibria at high pressures and high temperatures.

cond-mat.mtrl-sci↗

arXiv2014

Equation of state of single-crystal cubic boron phosphide

The 300 K equation of state of cubic (zinc-blende) boron phosphide BP has been studied by in situ single-crystal X-ray diffraction with synchrotron radiation up to 55 GPa. The measurements have been performed under quasi-hydrostatic conditions using a Ne pressure medium in a diamond anvil cell. A fit of the experimental p-V data to the Vinet equation of state yields the bulk modulus B0 of 179(1) GPa with its pressure derivative of 3.3(1). These values are in a good agreement with previous elastic measurements, as well as with semiempirical estimations.

cond-mat.mtrl-sci↗

arXiv2014

Thermoelastic Equation of State of Boron Suboxide B6O up to 6 GPa and 2700 K: Simplified Anderson-Grüneisen Model and Thermodynamic Consistency

p-V-T equation of state of superhard boron suboxide B6O has been measured up to 6 GPa and 2700 K using multianvil technique and synchrotron X-ray diffraction. To fit the experimental data, the theoretical p-V-T equation of state has been derived in approximation of the constant value of the Anderson-Grüneisen parameter δT. The model includes bulk modulus B0 =181 GPa and its first pressure derivative B0' = 6 at 300 K; two parameters describing thermal expansion at 0.1 MPa, i.e. a = 1.4x10-5 K-1 and b = 5x10-9 K-2, as well as δT = 6. The good agreement between fitted and experimental isobars has been achieved to the absolute volume changes up to 5% as compared to volume at standard conditions, V0. The fitted thermal expansion at 0.1 MPa is well consistent with the experimental data, as well as with ambient-pressure heat capacity cp, bulk modulus B0 and δT describing its evolution with volume and temperature. The fitted value of Grüneisen parameter γ = 0.85 is in agreement with previous empiric estimations for B6O and experimental values for other boron-rich solids.

cond-mat.mtrl-sci↗

arXiv2014

Self-propagating high-temperature synthesis of boron subphosphide, B12P2

Two new methods to produce nanopowders of B12P2 boron subphosphide by self-propagating high-temperature synthesis have been proposed. Bulk polycrystalline B12P2 with microhardness of HV = 35(3) GPa and stability in air up to 1300 K has been prepared by sintering these powders at 5.2 GPa and 2500 K.

cond-mat.mtrl-sci↗

arXiv2014

Self-propagating high-temperature synthesis of boron phosphide

A new method of producing boron phosphide (BP) submicron powders by self-propagating high-temperature reaction between boron phosphate and magnesium in the presence of an inert diluent (sodium chloride) has been proposed. Bulk polycrystalline BP with microhardness of HV = 28(2) GPa has been prepared by sintering the above powders at 7.7 GPa and 2600 K.

cond-mat.mtrl-sci↗

arXiv2013

Comment on "Thermodynamic properties of rock-salt ZnO" by Leitner et al. [Thermochimica Acta 572 (2013) 1-5]

Very recently Leitner et al. [Thermochimica Acta 572 (2013) 1-5] have tried to extract the thermodynamic data of rock-salt ZnO from ab initio and experimental data available in the literature. In this Comment we show that neglecting (i) the strongly pronounced kinetic features of the pressure-induced phase transition in ZnO at room temperature and (ii) results of calorimetric measurements available in the literature [Russ. Chem. Bull. 59 (2010) 325-328] makes the proposed set of thermodynamic functions completely incorrect.

cond-mat.mtrl-sci↗

arXiv2013

Low-temperature thermal expansion of rock-salt ZnO

Lattice parameter of metastable high-pressure phase of zinc oxide, rock-salt ZnO was measured in the 10-300 K temperature range using synchrotron X-ray powder diffraction. No phase transition was observed down to 10 K. The lattice parameter of rock-salt ZnO was found to increase from 4.266 Å in the 10-80 K range up to 4.2752(3) Å at 298 K, while the volume thermal expansion coefficient increases from slight negative values below 40 K up to 4.77\times10^-5 K^-1 at 298 K.

cond-mat.mtrl-sci↗

arXiv2013

Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction

During past years, a number of reports have been published on synthesis of tetragonal allotrope of boron, t-B52 phase. However, no unambiguous characterization of the crystal structure has been performed to the present time, while remarkable variation of the a/c lattice-parameter ratio raises strong doubts about its uniqueness. Here the Rietveld refinement of the crystal structure of the high pressure - high temperature boron phase synthesized by a direct solid-state transformation of rhombohedral beta-B106 at 20 GPa and 2500 K has been reported for the first time. Although this boron allotrope belongs to the t-B52 type, its structure can be considered as pseudo-cubic with the a/c ratio of sqr(2).

cond-mat.mtrl-sci↗

arXiv2012

On melting of silicon carbide under pressure

The melting of silicon carbide has been studied at pressures 5-8 GPa and temperatures up to 3300 K. It has been found that SiC melts congruently, and its melting curve has negative slope of -44 +/- 4 K/GPa.

cond-mat.mtrl-sci↗

arXiv2012

On melting of B4C boron carbide under pressure

The pressure dependence of melting temperatures for boron carbide and B4C-carbon eutectic has been studied up to 8 GPa, and it was found that in both cases the melting curves exhibit negative slope (-13\pm6 K/GPa), that is indicative of higher density of the melt as compared to the solid phase.

cond-mat.mtrl-sci↗

arXiv2011

Experimental study and critical review of structural, thermodynamic and mechanical properties of superhard refractory boron suboxide, B6O

In the present paper we performed the analysis of available data on structural, thermodynamic and mechanical properties of B6O. Although the compound is known for half a century and has been extensively studied, many properties of this boron-rich solid remain unknown or doubtful. Semi-empirical analysis of our experimental and literature data allowed us to choose the best values of main thermodynamic and mechanical characteristics among previously reported data, to predict the thermoelastic equation of state of B6O, and dependence of its hardness on non-stoichiometry and temperature.

cond-mat.mtrl-sci↗

arXiv2011

Comment on Zarechnaya et al. Pressure-induced isostructural phase transformation in gamma-B28. Phys. Rev. B 82, 184111 (2010)

Zarechnaya et al. claimed an isostructural transformation in gamma-B28 at about 40 GPa; below which the phase is more compressible (B0=227 GPa) and above which less compressible (B0=281 GPa) than in previous experiments or theory. Here we wish to point out some interesting questions related to these claims. Summarizing briefly our points, the suggestion of an isostructural transformation is inconsistent with ab initio calculations and experiment, we see no physical mechanism that could be responsible for such a transformation, and the evidence for it is self-contradictory.

cond-mat.mtrl-sci↗

arXiv2011

The high-pressure phase of boron, γ-B28: disputes and conclusions of 5 years after discovery

γ-B28 is a recently established high-pressure phase of boron. Its structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type arrangement (B2)δ+(B12)δ- and displays a significant charge transfer δ~0.5- 0.6. The discovery of this phase proved essential for the understanding and construction of the phase diagram of boron. γ-B28 was first experimentally obtained as a pure boron allotrope in early 2004 and its structure was discovered in 2006. This paper reviews recent results and in particular deals with the contentious issues related to the equation of state, hardness, putative isostructural phase transformation at ~40 GPa, and debates on the nature of chemical bonding in this phase. Our analysis confirms that (a) calculations based on density functional theory give an accurate description of its equation of state, (b) the reported isostructural phase transformation in γ-B28 is an artifact rather than a fact, (c) the best estimate of hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a significant degree of ionicity. Apart from presenting an overview of previous results within a consistent view grounded in experiment, thermodynamics and quantum mechanics, we present new results on Bader charges in γ-B28 using different levels of quantum-mechanical theory (GGA, exact exchange, and HSE06 hybrid functional), and show that the earlier conclusion about significant degree of partial ionicity in this phase is very robust.

cond-mat.mtrl-sci↗

arXiv2011

Thermodynamic aspects of materials' hardness: prediction of novel superhard high-pressure phases

In the present work we have proposed the method that allows one to easily estimate hardness and bulk modulus of known or hypothetical solid phases from the data on Gibbs energy of atomization of the elements and corresponding covalent radii. It has been shown that hardness and bulk moduli of compounds strongly correlate with their thermodynamic and structural properties. The proposed method may be used for a large number of compounds with various types of chemical bonding and structures; moreover, the temperature dependence of hardness may be calculated, that has been performed for diamond and cubic boron nitride. The correctness of this approach has been shown for the recently synthesized superhard diamond-like BC5. It has been predicted that the hypothetical forms of B2O3, diamond-like boron, BCx and COx, which could be synthesized at high pressures and temperatures, should have extreme hardness.

cond-mat.mtrl-sci↗

arXiv2010

New high-pressure form of boron is significantly ionic

The comment of Dubrovinskaia et al. is scientifically flawed. The high-pressure form of boron, discovered by Oganov et al., is indeed new and its bonding has a significant ionic character, as demonstrated in Ref. 1.

cond-mat.mtrl-sci↗

arXiv2009

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 percent of boron, and it was not until 1909 that 99-percent 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. Boron's complexities arise from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high-pressure experiments and ab initio evolutionary crystal structure predictions that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B12 clusters and the resultant charge transfer between them.

cond-mat.mtrl-sci↗