Explorations on TiOsX (X=B, C, N, O and Si) alloys for potential superhard materials from first-principle calculation

Using the first-principle calculations, we gained a deep insight of the structural, mechanical, electronic and thermal properties of the TiOs and TiOs-X (X=B, C, N, O and Si) compounds. The calculated results of formation enthalpy Hform and ternary transfer energy EXOs→Ti illustrate that O element exhibits strong Os site preference and all the compounds here are structurally stable. The results of mechanical properties confirm that there is no superhard character in those intermetallics which are mechanically stable. It is noted that the Ti7Os8Si possesses the best mechanical properties. All the compounds here show elastic anisotropy, and the Ti8Os7O exhibits the strongest elastic anisotropy, while the Ti8Os7Si strongly tends to be isotropic. There exists a mixture of covalent, ionic and metallic characters in these compounds. The covalent bond strength of Ti7Os8X is supposed to be better than that of the corresponding Ti8Os7X. Moreover, the minimum thermal conductivity kmin of these compounds are comparatively small and show dependence of directions, and they have potential thermal-insulating application in engineering.