Structural, electronic, and elastic properties of Y-diamonds and their BN analogues

The structural, elastic, and electronic properties of yne-diamonds a new group of covalent frameworks formed by sp(1) and sp(3) C atoms as well as their BN analogues are studied within the density-functional tight-binding method. The presence of very anisotropic non-equivalent covalent bonds (sp(1)-sp(3))/(sp(1)-sp(1)) in diamond-like skeletons of these materials leads to drastic changes in their properties as compared with the parent phases: diamond and c-BN. The most surprising finding concerns "pseudo-metallic" mechanical properties of examined yne-diamond-like C, BN crystals, since these wide-band-gap semiconductors behave as very soft, high-compressible, and ductile materials, showing a positive Cauchy pressure, quite high Poisson's ratio, and very small bulk moduli typical of metals. (C) 2013 Elsevier B.V. All rights reserved.