Abstract
We present a study of the thermodynamic and physical properties of Ta5Si3 compounds by means of density-functional theory based calculations. Among the three different structures (D8(m), D8(l), D8(8)), the D8(l) structure (Cr5B3 prototype) is the low-temperature phase with a high formation enthalpy of -449.20 kJ/mol, the D8(m) structure (W5Si3 prototype) is the high-temperature phase with a formation enthalpy of -419.36 kJ/mol, and the D8(8) structure (Mn5Si3 prototype) is a metastable phase. The optimized lattice constants of the different Ta5Si3 compounds are also in good agreement with the experimental data. The electronic density of states 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 Gruneisen parameter have also been obtained in the present work. The transformation temperature (2303.7 K) between the D8(m) and the D8(l) structures has been predicted by means of the Gibbs energy, and this predicted temperature (2303.7 K) is close to the experimental value (2433.5 K).