First Principle Study of Structural, Electronic, and Optical Properties of XIn2S4 (X = Zn, Cd, Hg)

The spinel oxides are one of the prime candidates for their use in thermoelectric and optoelectronic applications. This particular article mainly deals with the thermodynamic and mechanical stabilities of spinel sulfides confirmed by formation energy and Born-mechanical stability criteria. The ductile behavior is achieved through Poisson’s and Pugh's ratios. The indirect band gaps of 1.9 eV, 1.7 eV and direct band gap of 1.3 eV for ZnIn2S4, CdIn2S4 and HgIn2S4 spinel sulfides, respectively, are estimated by employing modified Becke-Johnson (mBJ) potential in the Wien2k computational program. The calculated optical characteristics such as dielectric coefficient, refractive index, absorption, reflection, energy loss coefficient and other related parametric quantities are explored to observe optoelectronic applications from UV to visible energy range as we move from Zn to Hg. Moreover, the ratios of thermal conductivity to electrical conductivity, Seebeck coefficient along with the figure of merits (ZT) are discussed to acknowledge the thermoelectric behavior of all three materials. The high values of ZT 0.84/0.74/0.79 are observed for Zn/Cd/HgIn2S4 spinel sulfides which ensure their prospective use in thermal energy conversion devices, especially in thermoelectric generators.