Deheng Shi

Theoretical study of the elastic properties of titanium nitride

The equilibrium lattice parameter, relative volume V/V0, elastic constants Cij, and bulk modulus of titanium nitride are successfully obtained using the ab initio plane-wave pseudopotential (PW-PP) method within the framework of density functional theory. The quasi-harmonic Debye model, using a set of total energy vs molar volume obtained with the PW-PP method, is applied to the study of the elastic properties and vibrational effiects. We analyze the relationship between the bulk modulus and temperature up to 2000 K and obtain the relationship between bulk modulus B and pressure at diffierent temperatures. It is found that the bulk modulus B increases monotonously with increasing pressure and decreases with increasing temperature. Moreover, the Debye temperature is determined from the non-equilibrium Gibbs functions.

First-principles calculations of LaNi5-xSnxHy intermetallics and intermediate phase

The crystal and electronic structures of LaNi4:75Sn0.25 intermetallics and LaNi4.5Sn0.5Hy (y=2.0, 2.5) intermediate phase have been investigated by the full-potential linearized augmented plane wave (FP-LAPW) method. Hydrogen occupation sites in LaNi4.5Sn0.5Hy have been determined based on Westlakes criterions: (1) the minimum hole radius is 0.04 nm; (2) the minimum H-H distance is 0.21 nm; as well as geometry optimizations and internal coordinates optimizations. We find that hydrogen atoms prefer to occupy the 12n*, 6m, 12o, 6m* sites in LaNi4.5Sn0.5H2.0 and the 6m*, 4h, 6m, 12o, 12n* sites in LaNi4.5Sn0.5H2.5. The specific coordinates of hydrogen atoms in LaNi4.5Sn0.5Hy are also determined. The results show that hydrogen atoms tend to keep away from tin atoms. The maximum hydrogen content decreases compared with LaNi5. The interactions between Sn and Ni with H play a dominate role in the stability of LaNi4.5Sn0.5-H system. Lattice expansion and increment of Fermi energy EF show that both Sn and H atoms decrease structural stability of these alloys.