First Principles Study of Electronic, Vibrational, Elastic, and Thermal Properties of ScAlx (X=1, 2, 3) Complexes

The structural, electronic, vibrational, elastic, and thermal properties of ScAl, ScAl₂, and ScAl₃ complexes in the Sc-Al alloy system have been investigated using density functional theory within the framework of QUANTUM ESPRESSO. The computed lattice parameters are in good agreement with previously reported data, affirming the reliability of the adopted computational approach. Cohesive and formation energy calculations reveal that all three complexes exhibit thermodynamic stability. A detailed analysis of the electronic band structure and projected density of states, performed using the PBE functional, confirms their metallic character. Phonon dispersion and density of states analysis further substantiate the dynamic stability of these materials. The elastic constants satisfy the Born criteria, indicating mechanical stability. Additionally, we comprehensively evaluated the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy ratio, sound velocity, and Debye temperature for each complex. Finally, the Debye vibrational energy, free energy, entropy, and heat capacity were analyzed over the temperature range of 0–800 K, providing insights into their thermal behavior. Across all thermodynamic properties, ScAl2 demonstrates the most prominent behavior (highest energy, entropy, and heat capacity), indicating it may have stronger phonon activity and bonding characteristics compared to ScAl and ScAl3.