CHARGE-DENSITY DETERMINATION IN TIAL-CR AND TIAL-V USING QUANTITATIVECONVERGENT-BEAM ELECTRON-DIFFRACTION

Effects of 5 at.% alloying with Cr and V on the electronic structure o f TiAl compounds are studied using convergent-beam electron diffractio n (CBED) in a transmission electron microscope. The quantitative CBED systematic row method is used to determine low-order structure factors in TiAl-V and TiAl-Cr. This method is based on pixel-by-pixel compari sons and refinement of theoretical and experimental CBED patterns. The quantitative CBED method is developed further; the definition and use of fit factors, the number of beams to include in the calculations an d how to treat the background From diffuse scattering are topics that are addressed in particular. The structure factors are determined with an accuracy of typically 0.3%. Charge-density maps for TiAl-V are fou nd to be similar to those for undoped TiAl, indicating strong Ti d-d d irectional bonding in the Ti(001) plane. TiAl-Cr has a more uniformly distributed charge density, and charge is moved from the Ti-Ti bond to in between second-nearest-neighbour atoms.