Tuning properties of In ₂ HgX ₄ (X = O, S) spinels via anion substitution: A first-principles study

This study employs first-principles density functional theory (DFT) to investigate the structural, electronic, optical, elastic and thermoelectric properties of indium–mercury chalcogenide spinels, In 2 HgX 4 (X [Formula: see text] O, S). Calculations using the WIEN2K package with the Perdew–Burke–Ernzerhof modified Becke–Johnson (PBE-mBJ) functional and IRelast module reveal that anion substitution (O [Formula: see text] S) strongly influences bonding, lattice parameters and mechanical properties. In 2 HgO 4 forms a denser and stiffer lattice with a wide band gap (1.13[Formula: see text]eV), high refractive index and superior thermal stability, making it suitable for optical coatings. In contrast, In 2 HgS 4 exhibits a larger lattice, narrower band gap (0.84[Formula: see text]eV), stronger light absorption in the UV–visible region, enhanced dielectric response and promising thermoelectric performance ([Formula: see text]) due to its low thermal conductivity and high-power factor. Phonon spectra confirm the dynamical stability of both compounds. These results establish clear structure–property relationships and demonstrate that targeted anion substitution can tailor spinel chalcogenides for applications ranging from high-temperature coatings (oxides) to photovoltaic and energy-harvesting devices (sulfides).