Computational Investigation of Ternary Na-V-VI₂ Chalcogenides and Their Thermoelectric Properties

Ternary chalcogenides have been of recent investigation for applications such as solar cells and thermoelectrics. We have computed the structural, energetic, electronic, optical, and thermoelectric properties of nine ternary Na-V-VI₂ chalcogenides, NaAX₂, where A represents As, Sb, Bi and where X represents S, Se, Te, using first principles methods based on density functional theory and beyond. Optimized lattice parameters have been computed using the generalized gradient approximation (GGA). Phonon density of states computed at zero-temperature shows that only four of the nine compounds, NaAsS₂, NaAsTe₂, NaSbS₂, and NaSbSe₂, are dynamically stable. Our computations for these structures show that their electronic and optical properties are highly anisotropic. In addition, thermoelectric properties such as Seebeck coefficient (S) and power factor were computed using Boltzmann statistics. The compounds are predicted to have promising thermoelectric properties at 300 K, indicating that these materials are desirable for thermoelectric applications. Particularly, NaAsTe₂ is predicted to have S = 425 μV/K. Experimental verification is suggested.