From ScPd3 to ScPt3: Evolution of band dispersion, Dirac crossings, and optical constants in ScPtxPd3−x alloys

The structural, mechanical, electronic, and optical properties of ScPt x Pd 3-x (x = 0-3) alloys were investigated using first‑principles DFT within the full‑potential linearized augmented plane wave (FP‑LAPW) method in WIEN2k. Structural and elastic parameters were evaluated using GGA, while GGA‑mBJ was employed for accurate electronic and optical descriptions. All alloys are nonmagnetic, dynamically stable, and crystallize in the cubic F‑43 m (L1 2 ) structure with nearly identical lattice parameters, consistent with the similar atomic radii of Pt and Pd. The bulk modulus increases steadily with Pt concentration, whereas the shear and Young’s moduli peak at x = 2, indicating maximum bond stiffness at intermediate compositions. Electronic‑structure analysis shows strong Pd 4d-Sc 3d hybridization in ScPd 3 and increasing Sc 3d-Pt 5d coupling with Pt substitution, leading to broadening of bands and reduced DOS at the Fermi level. The alloys exhibit metallic behavior with Dirac‑like crossings along W-K and a small SOC‑induced gap (~0.05 eV) in ScPt 3 . Optical spectra reveal two principal peaks in the imaginary dielectric function near 0.2 eV and 2.3 eV, corresponding to interband transitions, and a major optical‑conductivity peak in the visible range. The static dielectric constant and refractive index rise with Pt content, reflecting enhanced optical polarizability. Overall, Pt/Pd substitution effectively tunes bond strength, electronic hybridization, and optical response, offering composition‑driven control of dielectric, refractive, and reflectivity properties. The intermediate alloys ScPtPd 2 and ScPt 2 Pd are reported here for the first time, providing theoretical benchmarks for future studies and applications in optoelectronic, photonic, and coating materials.