First-principles investigation on the electronic, mechanical and lattice dynamical properties of novel AlNiX (X = As and Sb) half-Heusler alloys

Abstract

First-principles calculation is performed to study the structural stabilities, elastic, mechanical, and lattice dynamical properties for AlNiAs and AlNiSb novel half Heusler alloys. The LiAlSi (C1b-type) structure of AlNiX has been explored in three atomic arrangements (AlNiX-type1, AlNiX-type II, AlNiX-type III) and found that type III is energetically more favorable for both AlNiAs and AlNiSb. Also, the computed ferromagnetic (FM), non-magnetic (NM), and anti-ferromagnetic (AFM) states for AlNiAs and AlNiSb advocates NM states. The calculated formation energy indicates they possess thermodynamical stability. The calculated electronic properties indicate that both half Heusler alloys are metallic. The computed elastic constants follow the requirements of mechanical stability. The calculated mechanical properties predict that AlNiAs is more ductile than AlNiSb. The mechanical anisotropy is also predicted for both AlNiAs and AlNiSb by Zener anisotropic factor. The bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio are computed to discuss their elastic properties. The calculated positive phonon frequencies for both alloys indicate their stability in the LiAlSi-type phase. Raman and infrared phonon modes have also been identified for both the alloys.