Phase stability and physical properties ofTa5Si3compounds from first-principles calculations

Abstract

We present a study of the thermodynamic and physical properties of Ta 5 Si 3 compounds by means of density functional theory based calculations. Among the three different structures (D8 m , D8 l , D8 8 ), the D8 l structure (Cr 5 B 3 -prototype) is the low temperature phase with a high formation enthalpy of -449.20kJ/mol, the D8 m structure (W 5 Si 3 -prototype) is the high temperature phase with a formation enthalpy of -419.36kJ/mol, and the D8 8 structure (Mn 5 Si 3 -prototype) is a metastable phase. The optimized lattice constants of the different Ta 5 Si 3 compounds are also in good agreement with the experimental data. The electronic density of states (DOS) and the bonding charge density have also been calculated to elucidate the bonding mechanism in these compounds and the results indicate that bonding is mostly of covalent nature.The elastic constants of the D8 m and D8 l structures have been calculated together with the different moduli. Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion and the Grüneisen parameter have also been obtained in the present work. The transformation temperature (2303.7K) between the D8 m and the D8 l structures has been predicted by means of the Gibbs energy, and this predicted temperature (2303.7K) is close to the experimental value (2433.5K).

Elasticity and magnetocaloric effect inMnFe4Si3

“…Direct calculation of the averaged sound velocity in the sample is not possible due to the hexagonal structure. However, a lower and upper boundary can be obtained within Reuss and Voigt approximations, respectively [34,35]. The sound velocities obtained at different temperatures are depicted in figure 10 and compared with the sound velocities obtained by NIS.…”

“…The starting values for the fitting procedure were taken from the literature on the related Ta 5 Si 3 compound [34]. The resonances were extracted for every temperature step individually.…”

Elastic and thermodynamic properties of Mo2C polymorphs from first principles calculations

“…Here, elastic constants were calculated using a stress-strain approach based on the generalized Hooker's law. Moreover, the bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (σ) are obtained using Voigt-Reuss-Hill (VRH) approximation [22]. The results of elastic constants C ij , B, G, E and σ are shown in Table 2.…”

Physical properties of thermoelectric zinc antimonide using first-principles calculations

“…We have determined the bulk modulus from the fit of the E=f(V) data using the Vinet equation, as we have done for other materials previously [37]. With this method, we find a bulk modulus B EOS of 47.18 GPa and a pressure derivative B EOS 'of 5.35.…”

“…With this method, we find a bulk modulus B EOS of 47.18 GPa and a pressure derivative B EOS 'of 5.35. We have also determined all the elastic constants of ZnSb using the method described in detail in [37]. The strains used for the calculations together with the induced stresses are shown in Table 2.…”