Strain induced ductile to brittle transitions of NiNbAl half-Heusler alloy

Abstract

The present work is to explore the effect of strain on NiNbAl, half-Heusler alloy. We have investigated the properties of NiNbAl half-Heusler alloy using Density Functional Theory (DFT). The isotropic strains (tensile and compressive) are applied to examine the occurrence of phase transitions in the alloy. Induction of strain alters the electronic, mechanical and thermodynamic properties of the alloy. On application of strain, the alloy undergoes transition from semimetal to direct band gap semiconductor at 4 % tensile strain and semimetal to metallic transition at −6% compressive strains. This electronic phase transitions occur due to the change in the interatomic distance between the atoms in the alloy. It is found that the energy band gap value increases up to 12 % tensile strain and starts decreasing for the further increase in tensile strain. The mechanical properties of the alloy under strains are analysed and their variation under compressive and tensile strains are compared. The alloy undergoes ductile to brittle transitions on increasing the strain beyond 4 %. The phonon dispersion curves for different strains indicate that the alloy is thermodynamically stable under strain. The present results emphasis the effect of strain on electrons, phonons and the mechanical stability of the alloy which will pave way for designing flexible semiconducting devices with suitable device functionalities.