Mechanical properties of icosahedral boron carbide explained from first principles

Raucoules, Roman; Vast, Nathalie; Betranhandy, Emmanuel; Sjakste, Jelena

doi:10.1103/physrevb.84.014112

Cited by 32 publications

(44 citation statements)

References 33 publications

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“…The lattice parameters (angles) of B 2.5 C, as shown in Table II, are significantly smaller (larger) than those of B 4 C by approximately 5.4% (4%), corresponding to a decrease of unit-cell volume in B 2.5 C by 11.6%, as compared to that of B 4 C. Such a volume contraction in B 2.5 C is mainly due to the formation of diatomic carbon chains, instead of three-atom chains, commonly formed for boron carbides with at.% 20 [86]. For this reason, the existence of the carbon-richer phase B 2.5 C may be investigated by conventional diffraction techniques.…”

Section: E Synthesis Route Of B 25 C and Fingerprint For Its Characmentioning

confidence: 94%

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: E Synthesis Route Of B 25 C and Fingerprint For Its Characmentioning

confidence: 94%

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

2016

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“…Therefore, shear deformation preferentially takes place along this plane by the deformation and debonding of the three-atom chains when regular dislocation slip cannot be activated due to high Peierls stress at low temperatures. The occurrence of shearing along this plane may also be stimulated by the accumulation of thermal equilibrium point defects in the atomic chains 28 , which leads to the weakening of the chain structure. Likewise, multiple polyhedra of the chain structure (C-B-C, C-C-C, C-C-B and so on) 20 , together with the point defects (vacancies) in the chains, make this slip plane not have good long-range translational symmetry, and, hence, favourably form structure disorder when slip takes place.…”

Section: Discussionmentioning

confidence: 99%

Atomic structure of amorphous shear bands in boron carbide

et al. 2013

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Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

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“…The mechanism to produce the orientationally ordered monoclinic structure from the rotationally disordered rhombohedral structure might be concerted B-C exchanges [24] whose energy barriers must be of order 1eV, and hence are kinetically suppressed at temperatures substantially below melting. This may be why the monoclinic distortion has not been observed in diffraction experiments.…”

Section: Discussionmentioning

confidence: 99%

“…Configurations containing the well-known structure elements of B 12 , B 11 C 1 , and B 10 C 2 icosahedra, and containing C-B-C and C-B-B chains prove reasonably low in energy. The combination of a B 10 C 2 icosahedron with a B 12 icosahedron forms the bipolar defect [24]. All possible positions of carbon atoms within each icosahedron and chain are considered.…”

Section: First Principles Total Energy Calculationsmentioning

confidence: 99%

Prediction of orientational phase transition in boron carbide

Widom

Huhn

2012

Solid State Sciences

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The assessed binary phase diagram of boron-carbon exhibits a single intrinsically disordered alloy phase designated "B 4 C" with rhombohedral symmetry occupying a broad composition range that falls just short of the nominal carbon content of 20%. As this composition range is nearly temperature independent, the phase diagram suggests a violation of the third law of thermodynamics, which typically requires compounds to achieve a definite stoichiometry at low temperatures. By means of first principles total energy calculations we predict the existence of two stoichiometric phases at T=0K: one of composition B 4 C with monoclinic symmetry; the other of composition B 13 C 2 with rhombohedral symmetry. Using statistical mechanics to extend to finite temperatures, we demonstrate that the monoclinic phase reverts to the observed disordered nonstoichiometric rhombohedral phase above T=600K, along with a slight reduction on carbon content.

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Mechanical properties of icosahedral boron carbide explained from first principles

Cited by 32 publications

References 33 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

Atomic structure of amorphous shear bands in boron carbide

Prediction of orientational phase transition in boron carbide

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