Unveiling the Multifunctional Behavior of NaXTe2 (X = Al, Ga, In) Ternary Tellurides: A First-Principles Perspective

Abstract

This work presents a novel and in-depth first-principles investigation of the ternary telluride compounds NaXTe₂ (X = Al, Ga, In) with the aim to systematically uncover their structural, electronic, elastic, and optical characteristics. Using density functional theory calculations, we report for the first time, within a unified framework, a comparative analysis of these compounds crystallizing in the tetragonal I_4/mcm space group. Structural optimization yields lattice parameters in excellent agreement with experimental data, confirming the validity of the computational approach. A key finding of this study is the identification of direct band gaps at the Z point for all the investigated compounds, with significantly different values (1.28 eV for NaAlTe₂, 0.23 eV for NaGaTe₂, and 0.58 eV for NaInTe₂), which have not been consistently reported in the literature. The projected density of states reveals pronounced hybridization between the X and Te orbitals, shedding new light on the nature of covalent bonding in the lattice. From a mechanical standpoint, the full elastic tensor, including directional-dependent moduli, demonstrates the mechanical stability and ductility of these compounds, while also quantifying their moderate hardness — a desirable feature for practical integration in devices. Notably, optical analyses reveal a strong absorption in the ultraviolet range, accompanied by favorable dielectric responses and refractive indices, indicating high potential for these materials in ultraviolet-optoelectronic and photovoltaic applications. Overall, this study introduces new insights into the multifunctional behavior of NaXTe₂ compounds, establishes a reference dataset for future experimental validation, and highlights these materials as promising candidates for the development of next-generation semiconductors and optical devices.