Bismuth-based halide double perovskites for optoelectronic and photocatalytic applications

This study demonstrates the structural, mechanical, acoustic and thermal, electronic and optical properties of K 2 LiBiX 6 (X[Formula: see text]Cl, Br, I) bismuth-based halide double perovskites. The density functional theory (DFT)-based Full-potential linearized augmented plane wave (FP-LAPW) scheme is used, with the WIEN2k simulation code. These compounds possess a face-centered cubic crystal structure and satisfy the Goldschmidt tolerance and octahedral factor ([Formula: see text] and [Formula: see text] criteria. Negative formation enthalpy ([Formula: see text] confirms their thermodynamic stability. Elastic and mechanical investigations affirm their mechanical stability, brittleness and anisotropy, as indicated by Pugh’s ratio ([Formula: see text]), Poisson ratio ([Formula: see text], Cauchy pressure ([Formula: see text] and anisotropic factor ([Formula: see text]. Acoustic and thermal analyses based on sound velocities, Debye and melting temperatures and thermal expansion coefficient are reported. The electronic properties reveal indirect band gap semiconducting nature with band gaps of 4.67, 3.74 and 2.62[Formula: see text]eV for K 2 LiBiCl 6 , K 2 LiBiBr 6 and K 2 LiBiI 6 , respectively. Band gap tuning follows halogen ionic radius variation. Optical features, including the imaginary part of the dielectric constant and absorption coefficient, show peaks in the ultraviolet (UV) region, indicating potential in UV optoelectronics. Favorable band edge alignments with redox potential suggest these materials are promising for photocatalytic water splitting.