Crystal structure and physical properties of Ti2B5 predicted by first principles calculations.

[Display omitted] Applying the advanced CALYPSO structure searching method and first principles calculations, we predict a novel superhard structure for Ti 2 B 5 , which belongs to the monoclinic C 2/ m space group. The previously known Hf 2 B 5 , W 2 B 5 , and δ -V 2 O 5 -type structures are also selected as the potential structures for Ti 2 B 5. It is shown that the predicted C 2/ m structure is the most stable phase among these considered structures within the range of 0-100GPa. The calculations of the phonon dispersion and elastic constants affirm that the predicted C 2/ m phase is dynamically and mechanically stable. The predicted high shear modulus (249 GPa) and large hardness (46.9 GPa) show that it should be an underlying superhard material. In addition, the elastic anisotropy of Ti 2 B 5 is also explored by investigating the directional dependence of the Young's modulus, shear modulus, and Poisson's ratio as well as some well anisotropy indices. The particular analyses of the density of states and electron charge density distribution verify that the strong B-B and Ti-B covalent bonds in the predicted C 2/ m- Ti 2 B 5 phase play an important part in its hardness and structural stability. [ABSTRACT FROM AUTHOR]