The study of structural, elastic, electronic and optical properties of CsYx I(1-x) (Y = F, Cl, Br) using density functional theory

The structural, electronic, elastic and optical properties of CsYx I(1-x) (Y = F, Cl, Br) are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA). The ground state properties such as lattice constant (a(o)) and bulk modulus (K) have been calculated. The mechanical properties including Poisson's ratio (sigma), Young's modulus (E), anisotropy factor (A) and shear modulus (G) were also calculated. The results of these calculations are comparable with the reported experimental and theoretical values. The ductility of CsYx I(1-x) was analyzed using Pugh's rule (B/G ratio) and Cauchy's pressure (C-12-C-44). Our results revealed that CsF is the most ductile among the CsYxI(1-x) (Y = F, Cl, Br) compounds. The incremental addition of lighter halogens (Y-x) slightly weakens the strength of ionic bond in CsYxI(1-x). Moreover, the optical transitions were found to be direct for binary and ternary CsYxI(1-x). We hope that this study will be helpful in designing binary and ternary Cs halides for optoelectronic applications.