Electronic properties, high pressure phase stability and elastic anisotropy of BC5

Abstract

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-centered orthorhombic structure with the Space Group, Imm2. The second had a body-centered 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.

Keywords

• High pressure phase stability
• Elastic anisotropy
• Ultra-hard material