Hypothetically superhard boron carbide structures with a B<sub>11</sub>C icosahedron and three‐atom chain

Aydın, Sezgin; Şi̇mşek, Mehmet

doi:10.1002/pssb.200844328

Cited by 35 publications

(38 citation statements)

References 43 publications

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“…Demonstrated by several experimental and theoretical studies [1,11,[80][81][82], boron carbides can be superhard materials, with Vickers hardness exceeding 40 GPa. Considering that B 2.5 C has even higher values of elastic moduli than those of B 4 C, together with the experimental fact that hardness of boron carbide increases with the carbon content [83,84], one can expect the carbon-rich B 2.5 C to be a superhard material, likely even harder than B 4 C.…”

Section: B Configurational Disorder In B 25 Cmentioning

confidence: 99%

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

2016

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We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B 4 C to B 2 C, using first-principles calculations. Apart from B 4 C, generally addressed in the literature, B 2.5 C, represented by B 10 C p 2 (C-C), where C p and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B 4 C as well as pure boron and carbon phases. The thermodynamic stability of B 2.5 C is determined by the Gibbs free energy G as a function of pressure p and temperature T , in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B 2.5 C is then illustrated through the p-T phase diagrams. Depending on the temperatures, the stability range of B 2.5 C is predicted to be within the range between 40 and 67 GPa. At T 500 K, the icosahedral C p atoms in B 2.5 C configurationally disorder at the polar sites. By investigating the properties of B 2.5 C, e.g., elastic constants and phonon and electronic density of states, we demonstrate that B 2.5 C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B 2.5 C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

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Section: B Configurational Disorder In B 25 Cmentioning

confidence: 99%

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

2016

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“…Due to the the idealized carbon rich B 4 C (or B 12 C 3 ) stoichiometry, one would presume that boron atoms would be found in the icosahedra and the carbon atoms in the triatomic linker chains. Electronic structure calculations, primarily based upon density functional theory (DFT), [11][12][13][14][15][16][17][18] have shown the most stable atomic arrangement is where one of the boron atoms prefers to be located in the center of the three atom chain, the phase written as (B 11 C)CBC.…”

Section: Introductionmentioning

confidence: 99%

Equation of state, adiabatic sound speed, and Grüneisen coefficient of boron carbide along the principal Hugoniot to 700 GPa

et al. 2016

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A new equation of state (EOS) experimental technique that enables the study of thermodynamic derivatives into the TPa regime is described and applied to boron carbide (B 4 C). Data presented here are the first principal Hugoniot sound speed measurements reported using a laser-driven shock platform, providing a new means to explore the high-pressure off-Hugoniot response of opaque materials. The extended B 4 C Hugoniot suggests the presence of a new high-pressure phase, as recently predicted by molecular dynamics simulations, adding to the complexity of the existing phase diagram.

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“…Later it was shown by nuclear magnetic resonance (NMR) studies [35][36][37], x-ray [1,38] and neutron [39] diffractions that rather than B 12 (CCC), the structure unit of B 4 C should be represented by B 11 C(CBC), in which one of the boron atoms in the icosahedron is substituted by the chain-center carbon atom, yielding a B 11 C icosahedron linking to a (CBC) chain. Demonstrated by first-principles-based theoretical calculations [40][41][42][43][44], the B 11 C p (CBC) unit is most energetically favorable over the other B 4 C units, i.e. B 11 C e (CBC), B 12 (CCC), and B 11 C(CCB), where the superscript p and e denote the polar and equatorial sites of the icosahedron, respectively.…”

Section: Boron Carbidementioning

confidence: 99%

“…To visualize the relevant energy scale, rather than the ground-state energy, which depending on the definition can vary with thousands of eV, the formation energy with respect to pure phases is used, when plotting a convex hull. In the case of boron carbide, the ground state of B 13 C 2 , determined by the first-principles-based energy minimization, can be given by B 12 (CBC) [46][47][48], meanwhile it is B 11 C p (CBC) for B 4 C [ [40][41][42][43][44]. The convex hull of boron carbide, constructed based only on the two mentioned stoichiometries, is shown in Fig.4.1.…”

Section: Convex Hull and Formation Energymentioning

confidence: 99%

First-principles study of configurational disorder in icosahedral boron-rich solids

Ektarawong¹

2015

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This thesis is a theoretical study of configurationally disordered icosahedral boronrich solids, in particular boron carbides, using density functional theory and alloy theory. The goal is to resolve discrepancies, regarding the properties of boron carbides, between experiments and previous theoretical calculations which have been a controversial issue in the field of icosahedral boron-rich solids. For instance, B 13 C 2 is observed experimentally to be a semiconductor, meanwhile electronic band structure calculations reveal a metallic character of B 13 C 2 due to its electron deficiency. In B 4 C, on the other hand, the experimentally observed band gap is unexpectedly smaller, not the usual larger, than that of standard DFT calculations. Another example is given by the existence of a small structural distortion in B 4 C, as predicted in theoretical calculations, which reduces the crystal symmetry from the experimentally observed rhombohedral (R3m) to the based-centered monoclinic (Cm). Since boron carbide is stable as a single-phase over a broad composition range (∼8-20 at.% C), substitution of boron and carbon atoms for one another is conceivable. For this reason, the discrepancies have been speculated in the literature, without a proof, to originate from configurational disorder induced by substitutional defects. However, owing to its complex atomic structure, represented by 12-atom icosahedra and 3-atom intericosahedral chains, a practical alloy theory method for direct calculations of the properties of the relevant configurations of disordered boron carbides, as well as for a thermodynamic assessment of their stability has been missing.In this thesis, a new approach, the superatom-special quasirandom structure (SA-SQS), has been developed. The approach allows one to model configurational disorder in boron carbide, induced by high concentrations of low-energy B/C substitutional defects. B 13 C 2 and B 4 C are the two stoichiometries, mainly considered in this study, as they are of particular importance and have been in focus in the literature. The results demonstrate that, from thermodynamic considerations, both B 13 C 2 and B 4 C configurationally disorder at high temperature. In the case of B 13 C 2 , the configurational disorder splits off some valence states into the band gap that in turn compensates the electron deficiency in ordered B 13 C 2 , thus resulting in a semiconducting character. As for B 4 C, the configurational disorder eliminates the monoclinic distortion, thus resulting in the restoration of the higher rhombohedral symmetry. Configurational disorder can also account for an exceliii iv lent agreement on elastic moduli of boron carbide between theory and experiment. Thus, several of the previous discrepancies between theory and experiments are resolved.Inspired by attempts to enhance the mechanical properties of boron suboxide by fabricating boron suboxide-boron carbide composites, as recently suggested in the literature, the SA-SQS approach is used for modeling mixtures of boron sub...

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Hypothetically superhard boron carbide structures with a B₁₁C icosahedron and three‐atom chain

Cited by 35 publications

References 43 publications

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

Equation of state, adiabatic sound speed, and Grüneisen coefficient of boron carbide along the principal Hugoniot to 700 GPa

First-principles study of configurational disorder in icosahedral boron-rich solids

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Hypothetically superhard boron carbide structures with a B11C icosahedron and three‐atom chain

Cited by 35 publications

References 43 publications

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

Carbon-rich icosahedral boron carbides beyondB4Cand their thermodynamic stabilities at high temperature and pressure from first principles

Equation of state, adiabatic sound speed, and Grüneisen coefficient of boron carbide along the principal Hugoniot to 700 GPa

First-principles study of configurational disorder in icosahedral boron-rich solids

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Hypothetically superhard boron carbide structures with a B₁₁C icosahedron and three‐atom chain