Investigation of osmium carbides with various stoichiometries: First-principles calculations

Abstract

Using first-principles calculations, we have investigated osmium carbides with various stoichiometries (i.e., OsC, Os2C3, and OsC2). It is found that the predicted cubic OsC is of about 0.29 eV/(formula unit) lower in energy than previously proposed NiAs–OsC at ambient conditions. The plot of the computed enthalpy as a function of pressure indicates that cubic OsC is more stable than NiAs–OsC up to about 33 GPa. Moreover, cubic OsC shows a semiconductor character with a narrow gap of about 0.5 eV. The hypothetical P-4c2 and Pbcn Os2C3 show large incompressibility with their bulk moduli being about 360 GPa. P-4c2 Os2C3 exhibits the semiconductor character, while Pbcn Os2C3 metallic. Among the considered osmium carbides, the two hexagonal OsC2 have larger shear moduli, which indicates that they are potential superhard materials, and the total density of states suggest they are metallic. We have also discussed the dependence of shear modulus on carbon content. It was found that the shear modulus increases with the increased carbon content, and that the strong C–C bond in OsC2 is helpful to its high shear modulus. It is also found that a sublinear relationship exists between the Debye temperature and shear modulus.

Energetic, mechanical, and vibrational stability of metastable OsC phase

“…The first one is WC-OsC, which is claimed to be the experimentally observed crystal structure of OsC by Kempter and Nadler. 23 This FeSi structure is in cu-bic symmetry, which is, however, not consistent with the hexagonal x-ray characterization of the experimental observations. The third one is CoSn-structured OsC ͑CoSn-OsC͒, the elastic constants of which are all positive according to Guo et al's calculation.…”

Электронная структура, механическая и динамическая стабильность гексагональных субкарбидов M-=SUB=-2-=/SUB=-C (M = Tc, Ru, Rh, Pd, Re, Os, Ir, Pt): ab initio расчеты

“…Расчетные температуры Дебая субкарбидов изменя-ются в интервале от 289 K (для Pt 2 C) до ∼ 530 K для Tc 2 C и Ru 2 C. Эти значения в целом сопоставимы с θ D для моно-и дикарбидов тяжелых 4d-, 5d-металлов, см, например, [23,26]. Мы обнаружили (табл.…”

“…Гораздо меньше информации имеется о сверх-(C/M > 1) и субстехиометрических (C/M < 1) карбидах тяжелых 4d-, 5d-металлов [21][22][23][24][25][26][27][28]. Одним из наиболее интересных результатов является тот факт, что для некоторых субкарбидов M 4 C энергия формирования E form < 0 [24] и, таким образом, в отличие от монокар-бидов МС с E form > 0, углеродная стехиометрия может являться основным фактором, определяющим успешный синтез этих материалов.…”

Theoretical calculations on the structural, electronic, and optical properties of bulk silver nitrides

“…It is well‐known now that late transition‐metal nitrides (TMNs) usually possess interesting properties leading to a variety of potential technological applications . Hence, a significant number of quantum mechanical ab initio calculations of the structural and physical properties of this family of materials have appeared in the literature.…”