First-principles calculation of the electronic, optical, and photo-electrochemical properties of CaM2S4 (M = Sc, Y) compounds

Abstract

The orthorhombic CaM2S4 (M = Sc, Y) structures were investigated in the present work by first-principles calculations. CaM2S4 (M = Sc, Y) compounds are found to be mechanically stable with the anisotropic elastic constants that make them to be stable with respect to uniaxial deformation (Young’s moduli are 73.724 and 57.441 GPa for CaSc2S4 and CaY2S4, respectively) but easy to be undergone to shear deformation (Poisson’s ratios are 0.352 and 0.371 for CaSc2S4 and CaY2S4, respectively). Due to their relatively small direct energy band gaps (1.89 eV for CaSc2S4 and 2.26 eV for CaY2S4), the two compounds are intriguing candidates for long-wave transparency applications. The high hybridization degree of Ca-d, Y/Sc-d and S-p orbitals results in a wide energy range between the valence highest band and the conduction lowest band enabling these compounds to interact actively with visible and ultra-violet waves. The high absorption rate of 12–18 × 105 cm−1 and good hole-electron separation make CaM2S4 (M = Sc, Y) compounds to consider them good candidates for optoelectronic materials. Moreover, CaM2S4 (M = Sc, Y) compounds show good ability in the process of photo-driven photocatalyst water splitting.