Ab initio study of structural, optoelectronic, magnetic, and mechanical properties of Cs2KXBr6 (X = Mo, W): HDPs for spintronic and energy applications

The structural, optoelectronic, magnetic, and mechanical investigations of Cs2KXBr6 (X = Mo & W); halide double perovskites (HDPs), in the Fm-3m space group, have been conducted via an ab initio study. The formation energies per atom (eV) of Cs2KMoBr6 and Cs2KWBr6 are found to be − 1.72 and − 1.81, respectively. To reveal the accurate energy band gaps of the materials, the TB-mBJ potential is utilized. The electronic analysis reveals that both materials exhibit semiconducting behavior in both spin channels. The energy band gaps of Cs2KMoBr6 are 1.7 eV (up-spin) and 2.8 eV (down-spin), and Cs2KWBr6 are 1.6 eV (up-spin) and 3.3 eV (down-spin). The Phonon dispersion analysis and ab initio molecular dynamics simulations reveal the dynamical stability of the materials. The ferromagnetic (FM) and antiferromagnetic (AFM) natures of Cs2KWBr6 and Cs2KMoBr6 have been predicted, respectively. The net magnetic moment (µB) of the ground state of Cs2KWBr6 and Cs2KMoBr6 is 3 and 0, respectively. The mechanical analysis reveals that Cs2KWBr6 exhibits higher structural stability compared to the Cs2KMoBr6 material. The computed optical properties indicate that the materials have high absorption with a maximum of 140 cm−1 at 13.5 eV, a peak refractive index of 1.9 between 4.5 and 5.8 eV, and a maximum reflectivity of about 0.40 at high energy, which makes them promising candidates for high-energy region and moderate refractive indices, suggesting potential relevance for optoelectronic applications. In addition, the spin-dependent electronic structure and magnetic ordering indicate possible applicability in spin-dependent electronic systems. However, further device-level investigations are required to fully assess their technological performance.