Determination of Bonding Charge Density in NiAl by Quantitative Convergent Beam Electron Diffraction

Abstract

Quantitative convergent beam electron diffraction was applied to measure the twelve lowest indexed electron structure factors of NiAl. The experiments were carried out at 110 K. The electron structure factors were converted to X-ray structure factors which are the Fourier coefficients of the total electron charge density. For the five lowest coefficients the experimental error is 0.1 to 0.4% (after conversion). To obtain the bonding charge density, a reference was synthesized by superposing the charge densities of free, neutral, spherical atoms as computed by a relativistic Dirac-Fock program. The difference charge density exhibits mainly covalent bonding and a depletion of charge mainly in the Al core region. The difference charge density computed from the higher indexed coefficients cannot be explained by bonding effects but indicates that free neutral atoms might not be the best choice for the reference.