Phononic and thermodynamic properties of the sulvanite compounds: A first-principles study

Abstract

We have calculated the phononic and thermodynamic properties of the sulvanite family: Cu3TMX4 (TM=V, Nb, Ta; X=S, Se) using first-principles phonon calculations within the Density Functional Theory and the quasi-harmonic approximation. General trends in the phonon dispersion relation, the partial density of states, the thermal expansion and the heat capacity at constant pressure are discussed for these compounds. Our calculated frequencies at Γ are in good agreement with the available experimental Raman spectra, especially for the high-frequency A1 and F2d modes. Finally, at low-temperature when Se replaces S, it is observed that the broad peak of the heat capacity is almost a factor of two larger.