Y.H. Duan

Anisotropic elastic properties of MB (M = Cr, Mo, W) monoborides: a first-principles investigation

Abstract First principles calculations were performed to systematically investigate structure properties, phase stability and mechanical properties of MB (M = Cr, Mo, W) monoborides in orthorhombic and tetragonal structures. The results of equilibrium structures are in good agreement with other available theoretical and experimental data. The elastic properties, including bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν were calculated by the Voigt-Reuss-Hill approximation. All considered monoborides are mechanically stable. The results of elastic anisotropies show that elastic anisotropy of orthorhombic structure is larger than that of tetragonal structure. Moreover, the minimum thermal conductivities were also estimated using the Cahill’s model, and the results indicate that the minimum thermal conductivities show a dependence on directions.

Structural properties, phase stability, elastic properties and electronic structures of Cu–Ti intermetallics

The structural properties, phase stabilities, anisotropic elastic properties and electronic structures of Cu–Ti intermetallics have been systematically investigated using first principles based on the density functional theory. The calculated equilibrium structural parameters agree well with available experimental data. The ground-state convex hull of formation enthalpies as a function of Cu content is slightly symmetrical at CuTi with a minimal formation enthalpy (–13.861 kJ/mol of atoms), which indicates that CuTi is the most stable phase. The mechanical properties, including elastic constants, polycrystalline moduli and anisotropic indexes, were evaluated. G/B is more pertinent to hardness than to the shear modulus G due to the high power indexes of 1.137 for G/B. The mechanical anisotropy was also characterized by describing the three-dimensional (3D) surface constructions. The order of elastic anisotropy is Cu4Ti3 > Cu3Ti2 > α-Cu4Ti > Cu2Ti > CuTi > β-Cu4Ti > CuTi2. Finally, the electronic structures were discussed and Cu2Ti is a semiconductor.

Phase stability, anisotropic elastic properties and electronic structures of C15-type Laves phases ZrM2 (M = Cr, Mo and W) from first-principles calculations

Abstract Systematic investigations of phase stability and mechanical properties of C15-type ZrM2 (M = Cr, Mo and W) Laves phases were performed using first-principles calculations. The formation enthalpies of ZrM2 are in good agreement with the theoretical and experimental values. The elastic properties, including elastic constants and moduli, Poisson’s ratio and B/G, were discussed. The elastic anisotropy was also investigated via the anisotropy indexes (AU, AZ, Ashear and Acomp), the anisotropy of shear modulus and the 3D construction of bulk and Young’s moduli. The elastic anisotropy of ZrM2 is in order of ZrCr2 < ZrMo2 < ZrW2. The variations in the shear modulus and hardness show similar trends with increasing values from ZrCr2 to ZrW2. The electronic structures for these C15-type Laves phases were analysed to obtain deeper understanding of chemical bonds and phase stabilities. Finally, the sound velocities and Debye temperatures were also investigated.

Structural and anisotropic elastic properties of hexagonal MP (M = Ti, Zr, Hf) monophosphides determined by first-principles calculations

Abstract First-principles calculations were performed to investigate the structural properties, phase stabilities, elastic properties and thermal conductivities of MP (M = Ti, Zr, Hf) monophosphides. These monophosphides are thermodynamically and mechanically stable. Values for the bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν were calculated by Voigt–Reuss–Hill approximation. The mechanical anisotropy was discussed via several anisotropy indices and three-dimensional (3D) surface constructions. The order of elastic anisotropy is ZrP > HfP > TiP. The minimum thermal conductivities of these monophosphides were investigated using Clarke’s model and Cahill’s model. The results revealed that these monophosphides are suitable for use as thermal insulating materials and that their minimum thermal conductivities are anisotropic.

Elastic properties and thermal conductivities of fluor-, chlor- and brom-barium apatites predicted by first-principles simulations

Abstract First-principles calculations based on density functional theory were employed to investigate the anisotropic elastic properties and thermal conductivities of barium apatite Ba10(PO4)6X2 (X = F, Cl and Br). The bulk, Young’s and shear moduli were predicted. The results of anisotropic indexes and 3-D figures of bulk modulus and Young’s modulus show that the order of degree of elastic anisotropy is Ba10(PO4)6F2 < Ba10(PO4)6Cl2 < Ba10(PO4)6Br2. The thermal conductivities obtained from the Clarke’s model and Cahill’s model reveal that Ba10(PO4)6F2 has the largest thermal conductivity, and Ba10(PO4)6Br2 possesses the smallest one. The anisotropy of thermal conductivity indicates that the thermal conductivity in the (0 0 0 1) plane is larger than that in the plane.