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Unrelaxed unit cell crystal structures of, (a) C 7 B, (b) C 3 B (or C 6 B 2 ), (c) C 5 B 3 and (d) CB (or C 4 B 4 ).
Source publication
A number of potentially ultra-hard materials are examined using ab-initio methods. Compound phases of varying lattice stoichiometry in the B-C-N-O quaternary system, in the forms, C8−xBx (x = 1, 2, 3, 4), C7−xBNx (x = 1, 2, 3) and C6−xBNOx (x = 1, 2) are proposed as possible ultra-hard materials with useful applications. Cell structures and elastic...
Contexts in source publication
Context 1
... ultra-hard materials. Crystal structure diagrams were constructed for all the materials, before a relaxation process was carried out, using the crystalline structure visualization and analyzer software package, Xcrysden [32]. Unrelaxed unit cells of C 7 B, C 3 B (or C 6 B 2 ), C 5 B 3 and CB (or C 4 B 4 ) as simulated by Xcrysden are shown in Fig. ...
Context 2
... formula in the form, C 8-x B x for a particular value of x is obtainable from the unit cell diagrams in Fig. 1, considering that the atoms at the corners and faces contribute 1/8 and 1/2 of their volume to the cell, respectively. A relaxation operation was carried out on each of the unit cell structures using Quantum Espresso. In this way the atomic positions were allowed to self-adjust according to the interatomic forces until equilibrium of the system was ...
Citations
... The predominant atomic binding mechanism in super-hard materials is covalent bonding. The constituent atomic elements in these materials are often light, like C, B, O, and N [6] which are chemically suited for covalent bonding [7]. Since covalent bonds are generally directional and short, the light elements are able to form highly shear resistant threedimentional networks. ...
We have used Particle Swarm Optimization (PSO) crystal lattice structure searching and first-principles structural optimization to explore polymorphs of BC5, possessing sp³ hybridization, under a varying applied hydrostatic pressure from 0 to 1400 kbars. Three low Gibbs free energy structures were identified. The first had a body-centred orthorhombic structure with the Space Group, Imm2. The second had a body-centred tetragonal structure with the Space Group, I4¯m2 and thirdly a structure with a primitive trigonal Space Group, P3m1. Dynamical and mechanical stabilities were established for the Imm2, orthorhombic BC5 (o-BC5) structure using its phonon dispersions and elastic constants. The bulk modulus of this predicted BC5 phase was 374.30, which is high enough to indicate a super-hard compound. The material is brittle with a B/G ratio of 1.002 and a low degree of elastic anisotropy with a Universal Elastic Anisotropy Index of 2.946 %. Our electronic structure study shows that o-BC5 presents metallicity with a likely increase in electron-type conductivity with increased applied pressure.
