Structural, Electronic and Optical Properties of the Zintl-Phases NaXSb (X= Sr, Ba)

Theoretical investigations are conducted on the structural characteristics, electronic properties, and optical behaviors of NaSrSb and NaBaSb compounds, which are hexagonal ternary zintl phases. In this research, the plane-wave ultra-soft pseudopotential approach is utilized under the principles of density functional theory, incorporating generalized gradient approximation. Calculated equilibrium structural parameters closely match experimental data, supporting the reliability of the findings. Examination of the energy bands indicates that both substances, NaSrSb and NaBaSb, function as semiconductors with direct band gaps measured at 0.88 e V and 0.60 eV, respectively. Through the density of states analysis, it becomes evident how each elemental atom contributes to the electronic configuration within the energy bands. Notably, the upper valence sub-band is predominantly composed of (s,p)-Sb states, while the lower conduction band primarily features d-X and s-Sb states. Examination of the charge density underscores a primarily covalent character between Sr and Sb atoms, contrasting with the ionic bonding between N a and Sr\Zn atoms. Furthermore, the study extensively investigates the optical characteristics, analyzing frequency-dependent linear optical parameters, including the dielectric function, refractive index, extinction coefficient, reflectivity, and absorption coefficient. Notable absorption characteristics are observed in visible and ultraviolet ranges for both N aSrSb and N aBaSb compounds under [100] and [001] polarizations.