Charge Density Determination for Al-rich Composition L1o-ordered gamma-TiAl by Convergent Beam Electron Diffraction

The electron density difference map, ∆ρ(r)= ρ(r)Cryst ρ(r)IAM, here defined as the difference between the electron density of a crystal, ρ(r)Cryst, and that of the equivalent independent atom model (IAM), ρ(r)IAM, represents one of the quantum mechanical characteristics central for developing fundamental understanding of materials. Convergent beam electron diffraction (CBED) experiments performed with modern transmission electron microscope (TEM) instruments equipped with energy filter and charge coupled devices (CCD) permit probing of nano-scale volumes of perfect crystal and have been shown to enable the measurements of low-order structure factor, Fg, with sufficient accuracy to obtain Δρ(r) for 3d-electron system transition metals (e.g. Cr, Fe, Co, Ni) and some binary intermetallic phases (e.g. NiAl, TiAl and FePd) [1, 2]. The facility to determine experimentally the Δρ(r) for these d-electron materials warrants use of the CBED measurements as additional metrics in validation of density functional theory (DFT) calculations [2].