Theoretical study of mechanical and thermodynamic properties of titanium oxides TixOy

Abstract

The mechanical and thermodynamic properties of titanium oxides (TiO2, Ti2O3, TiO, Ti2O, Ti3O) are calculated by first-principles using density functional theory. All oxides show anisotropic elasticity in different crystallographic directions, while Ti2O3 is approaching to isotropy structure. The Young's modulus and theoretical hardness of Ti-O compounds decrease in the following order: TiO > Ti2O > TiO2 > Ti2O3 > Ti3O. The hardness of TiO is higher than common iron matrix like pearlite or martensite steels, only slightly lower than zirconia toughened alumina (ZTA) ceramics. The mechanical properties of ZTA/iron composite materials will be benefit from the interfacial TiO phase. The intrinsic ductility of Ti-O binary compounds is evaluated by the B/G ratio. Typically, Ti2O3 and Ti3O show ductile nature. The linear thermal expansion coefficients (LTECs) of the oxides are estimated by quasi-harmonic approximation (QHA). The computed LTECs are 6.55 × 10−6 K−1, 5.36 × 10−6 K−1, 8.22 × 10−6 K−1, 8.01 × 10−6 K−1 and 6.81 × 10−6 K−1 for TiO2, Ti2O3, TiO, Ti2O and Ti3O, respectively. These results of TiO2 and Ti2O3 are similar with the experimental data, whereas the experimental values of other titanium oxides are absent. Other thermodynamic properties such as specific heats (CV and CP) and thermal conductivities are also discussed.