Prediction of New Superhard Boron-Rich Compounds

Abstract

Boron solids exhibit a fascinating geometric and electronic structure. The properties of alpha-rhombohedral boron can be significantly changed by the addition of other atomic constituents. It is found that Pauling's bond valence principle plays an important role in designing boron-rich semiconductors. We have designed the novel boron-rich phases B12N2X (X = Zn, Cd, Be) with the boron carbide type structure by combining Pauling's bond valence principle with first-principles techniques. Their energy gaps, bulk moduli, microhardnesses, and total energies have been calculated. The results show that they are new superhard materials and potential semiconductors. It has been elucidated why B12N2 is metallic but B12N2Be is a semiconductor. This should open up new potential areas for predicting novel boron-rich compounds for industrial applications.

Hardness Prediction and First Principle Study of Re-123(Re = Y, Eu, Pr, Gd) Superconductors

“…[8][9][10][11] Recently, a new definition of the hardness of covalent crystals has been presented. [12][13][14][15] This paper gives a theoretical prediction of hardness values of these crystals by using the chemical bond theory of complex crystals and hardness theory. It helps to understand further the other mechanical properties.…”

First‐principles calculations of the mechanical properties of boron‐rich compounds B12N2X (X = Be, Zn, Cd)

“…The k-points of 6 × 6 × 6 were generated using the Monkhorst-Pack scheme [13] with a grid of 0.04 Å -1 . The compounds B 12 N 2 X, where X = Be, Zn, Cd, with the boron carbide (B 13 C 2 )-type structure, are built up of B 12 icosahedra linked together by N-X-N chains [8,9]. The zero-pressure single elastic constants of B 12 N 2 X (X = Be, Zn, Cd) were calculated from stress (σ) changes caused by very small strain (ε) through the relation C ij = σ i /ε j [14], as presented in Table 1.…”

“…Recently boron-rich compounds B 12 N 2 X (X = Be, Zn, Cd) with the boron carbide-type structure have been theoretically designed and predicted to be potential superhard semiconducting materials [8,9]. Moreover, the band gap changes with the introduction of the different metal atoms.…”

Microscopic models of hardness

“…Thus, α-boron has 4 bond types. B 12 can be decomposed into the sum of pseudobinary crystals as follows [77,78]:…”