Systematic first-principles study of impurity hybridization in NiAl

TL;DR

This study uses first-principles calculations to analyze how various impurity atoms affect bonding and hybridization in NiAl, revealing differences between embrittling and cohesion-enhancing impurities based on orbital behavior and charge transfer.

Contribution

It provides a systematic computational analysis of impurity effects on orbital hybridization and bonding in NiAl, highlighting the role of orbital localization and charge transfer in embrittlement.

Findings

Embrittlers like N and O have localized 2s orbitals that do not participate in bonding.

Cohesion enhancers like B and C show delocalized 2s orbitals contributing to bonding.

Impurities tend to acquire negative charge, reducing available electrons for covalent bonding.

Abstract

We have performed a systematic first-principles computational study of the effects of impurity atoms (boron, carbon, nitrogen, oxygen, silicon, phosporus, and sulfur) on the orbital hybridization and bonding properties in the intermetallic alloy NiAl using a full-potential linear muffin-tin orbital method. The matrix elements in momentum space were used to calculate real-space properties: onsite parameters, partial densities of states, and local charges. In impurity atoms that are empirically known to be embrittler (N and O) we found that the 2s orbital is bound to the impurity and therefore does not participate in the covalent bonding. In contrast, the corresponding 2s orbital is found to be delocalized in the cohesion enhancers (B and C). Each of these impurity atoms is found to acquire a net negative local charge in NiAl irrespective of whether they sit in the Ni or Al site. The embrittler therefore reduces the total number of electrons available for covalent bonding by removing some of the electrons from the neighboring Ni or Al atoms and localizing them at the impurity site. We show that these correlations also hold for silicon, phosporus, and sulfur.