First-principles investigation of structural, electronic, optical, and mechanical properties of novel metallic ternary halides K3XBr6 (X = Sc, Y)

Abstract

This study investigates the structural, electronic, optical, and mechanical properties of novel ternary halide compounds K₃XBr₆ (X = Sc, Y) using the FP-LAPW method within the WIEN2k framework. Structural analysis confirms their cubic symmetry, with optimized lattice parameters obtained via the Birch-Murnaghan equation of state, indicating greater structural stability for K₃YBr₆ compared to K₃ScBr₆. The calculated formation energies of − 1.325  eV/atom for K₃ScBr₆ and − 2.012  eV/atom for K₃YBr₆ confirm their thermodynamic stability. Furthermore, the absence of imaginary frequencies in the phonon dispersion spectra verifies their dynamic (phonon) stability. Electronic calculations reveal that both compounds exhibit metallic behavior, with overlapping valence and conduction bands. K₃ScBr₆ demonstrates higher carrier mobility, while K₃YBr₆ offers a better overall balance of physical and electronic characteristics. The valence band structure is predominantly shaped by bromine p-orbital contributions, which play a central role in the electronic behavior. Optical analysis highlights their potential in optoelectronic applications such as lasers, solar cells, and plasmonic devices, with K₃ScBr₆ optimized for ultraviolet response and K₃YBr₆ covering both ultraviolet and visible regions. Mechanical evaluation shows that K₃ScBr₆ is harder, stiffer, and more brittle, whereas K₃YBr₆ is softer, more ductile, and exhibits higher metallicity. These results position K₃XBr₆ (X = Sc, Y) as promising candidates for next-generation electronic, optoelectronic, and photonic technologies.