Fundamental properties of Ti6Si2B-a new ternary phase in the Ti-Si-B system

Density functional theory studies combined with the method of quasi-harmonic phonons have been undertaken to describe structural, bonding, elastic, vibrational and thermal properties of Ti6Si2B, which is a new ternary phase in the Ti-Si-B system. Analysis of the results is performed in relation to selected compounds from the Ti-Si and Ti-B systems as well as available experimental data. Titanium borosilicide exhibits covalent-type bonds of different strength as indicated by the calculated electron localization functions and the Bader charges. Its elastic and thermal properties are anisotropic due to higher out-of-plane than in-plane lattice compressibility and thermal expansivity. Polycrystalline Ti6Si2B is predicted to be a brittle material with quite high Vicker's hardness. It is shown that on one hand Ti6Si2B shares many common features with titanium silicides and borides, but on the other hand its mechanical, vibrational and thermal properties are distinct from those of compounds forming the Ti-Si and Ti-B systems. Theoretical phonon and Raman spectra, which are simulated at conditions close to experimental ones, may serve as a guide for interpretation and refinement of experimental spectra as well as symmetry mode assignment. The present work can be considered as a prediction study, still awaiting an experimental verification.