Preparation of boron microcrystals via high-pressure, high-temperature pyrolysis of decaborane, B10H14

Екимов, Е. А.; Зибров, И. П.; Zoteev, A. V.

doi:10.1134/s0020168511110069

Cited by 18 publications

(21 citation statements)

References 12 publications

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“…Similar B−H−B bridge structures were reported before for hydrogen in α-R boron [33]. The distance from an (8i) site to an apex atom of nearest B 12 figure 3) is short of three electrons to completely fill up the valence band and eight empty states (four bands) appear in the band gap [19]. The character of two of these in-gap bands corresponds to p-orbitals of (2b)-site B atoms that are oriented along the c-axis.…”

Section: Properties Of Hydrogenated α-T Boron 31 Bonding and Vibratsupporting

confidence: 82%

“…However, Hayami and Otani theoretically showed that α-T boron can be stabilized if the boron content is changed to B 52 [10]. At the same time several experimental works, mostly employing high-pressure high-temperature (HPHT) methods, reported the synthesis of α-T B 52 [11][12][13][14][15][16][17]. The HPHT synthesis was not used in the early days, and it is therefore likely that α-T boron is thermodynamically stable at high pressure and high temperature [18].…”

Section: Introductionmentioning

confidence: 99%

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Hydrogenation, dehydrogenation of α-tetragonal boron and its transition to δ-orthorhombic boron

Uemura¹,

Shirai²,

Kunstmann³

et al. 2019

J. Phys. Mater.

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Boron bulk crystals are marked by exceptional structural complexity and unusual related physical phenomena. Recent reports of hydrogenated α-tetragonal and a new δ-orthorhombic boron B 52 phase have raised many fundamental questions. Using density functional theory calculations it is shown that hydrogenated α-tetragonal boron has at least two stable stoichiometric compositions, B 51 H 7 and B 51 H 3 . Thermodynamic modeling was used to qualitatively reproduce the two-step phase transition reported by (Ekimov et al 2016 J. Mater. Res. 31, 2773) upon annealing, which corresponds to successive transitions from B 51 H 7 to B 51 H 3 to pure B 52 . The so obtained δ-orthorhombic boron is an ordered, low-temperature phase and α-tetragonal boron is a disordered, high-temperature phase of B 52 . The two phases are connected by an order-disorder transition, that is associated with the migration of interstitial boron atoms. Atom migration is usually suppressed in strongly bound, covalent crystals. It is shown that the migration of boron atoms is likely to be assisted by the migration of hydrogen atoms upon annealing. These results are in excellent agreement with the above mentioned experiment and they represent an important step forward for the understanding of boron and hydrogenated boron crystals. They further open a new avenue to control or remove the intrinsic defects of covalently bound crystals by utilizing volatile, foreign atoms.

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Section: Properties Of Hydrogenated α-T Boron 31 Bonding and Vibratsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Hydrogenation, dehydrogenation of α-tetragonal boron and its transition to δ-orthorhombic boron

Uemura¹,

Shirai²,

Kunstmann³

et al. 2019

J. Phys. Mater.

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“…Recrystallization of α-B 12 from β-B 106 was experimentally observed at much higher temperatures at both ambient (from melts containing Pt45) and high (during solid-state transformation12) pressures. Finally, t-B 52 has been recently obtained at ambient12 and high121314 pressures, and even recovered as a single phase1214. Although this tetragonal allotrope has been interpreted as a metastable one as compared to mysterious "HPHT t-B 192 ", our recent results showed that the latter has a crystal structure related in many aspects to t-B 52 phase, rather than to t-B 192 46.…”

mentioning

confidence: 68%

“…β'- and β″-B4, t-B 50 5, "HP form" of Wentorf6, "HPHT form" of t-B 192 7, etc. At present time only five allotropes are generally accepted: rhombohedral α-B 12 (α-phase)8 and β-B 106 (β-phase)9, orthorhombic γ-B 28 (γ-phase)10, tetragonal t-B 192 11 and t-B 52 (t-phase in this paper)5121314. t-B 52 has been proved to exist only very recently and its crystal structure has not been unambiguously established so far.…”

mentioning

confidence: 92%

Equilibrium p-T Phase Diagram of Boron: Experimental Study and Thermodynamic Analysis

Solozhenko

Kurakevych

2013

Sci Rep

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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). The positions of two triple points have been experimentally estimated, i.e. β–t'–L at ~ 8.0 GPa and ~ 2490 K; and β–γ–t' at ~ 9.6 GPa and ~ 2230 K. Finally, the proposed phase diagram explains all thermodynamic aspects of boron allotropy and significantly improves our understanding of the fifth element.

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“…The deviation from stoichiometry is expressed as B 52+δ , with a small fractional number δ. Incidentally, several articles reporting the synthesis of pure α-T boron have been published. [16][17][18][19][20][21] These newly discovered α-T forms should be seen as distinct from the traditional boron, because in most actually a series of crystals containing a C coagent ranging from 0 to 5 at.%. 19 Hyodo analyzed Kirihara's samples, reporting a slight non-stoichiometry (δ=+0.2).…”

Section: Theoretical Background and Experimental Factsmentioning

confidence: 99%

Structure, nonstoichiometry, and geometrical frustration ofα-tetragonal boron

et al. 2016

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Recent discoveries of supposedly pure α-tetragonal boron require to revisit its structure. The system is also interesting with respect to a new type of geometrical frustration in elemental crystals, which was found in β-rhombohedral boron. Based on density functional theory calculations, the present study has resolved the structural and thermodynamic characteristics of pure α-tetragonal boron. Different from β-rhombohedral boron, the conditions for stable covalent bonding (a band gap and completely filled valence bands) are almost fulfilled at a composition B 52 with two 4c interstitial sites occupied. This indicates that the ground state of pure α-tetragonal boron is stoichiometric. However, the covalent condition is not perfectly fulfilled because non-bonding ingap states exist that cannot be eliminated. The half occupation of the 4c sites yields a macroscopic amount of residual entropy, which is as large as that of β-rhombohedral boron. Therefore, α-tetragonal boron can be classified as an elemental crystal with geometrical frustration. Deviations from stoichiometry can occur only at finite temperatures. Thermodynamic considerations show that deviations δ from the stoichiometric composition (B 52+δ ) are small and positive. For reported high-pressure syntheses conditions δ is predicted to be about 0.1 to 0.2. An important difference between pure and C-or N-containing α-tetragonal boron is found in the occupation of interstitial sites: the pure form prefers to occupy the 4c sites, whereas in C-or N-containing forms a mixture of 2a, 8h, and 8i sites are occupied. The present article provides relations of site occupation, δ values, and lattice parameters, which enable us to identify pure α-tetragonal and distinguish the pure form from other ones.

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Preparation of boron microcrystals via high-pressure, high-temperature pyrolysis of decaborane, B10H14

Cited by 18 publications

References 12 publications

Hydrogenation, dehydrogenation of α-tetragonal boron and its transition to δ-orthorhombic boron

Hydrogenation, dehydrogenation of α-tetragonal boron and its transition to δ-orthorhombic boron

Equilibrium p-T Phase Diagram of Boron: Experimental Study and Thermodynamic Analysis

Structure, nonstoichiometry, and geometrical frustration ofα-tetragonal boron

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