Charge density and chemical bonding in rutile, TiO₂

The low-order structure factors of rutile (TiO₂) have been measured with an accuracy of up to 0.09% by quantitative convergent-beam electron diffraction (QCBED). This error is an order of magnitude smaller than that in conventional Bragg X-ray diffraction and equivalent to the accuracy of the X-ray Pendellösung method. It is sufficient to distinguish atomic, covalent and ionic bonding. By refinement of the combined data of low-order reflections measured by electron diffraction with high-order reflections from X-ray diffraction, accurate charge-density maps are obtained and used to understand the role of the 3d electrons in Ti-O bonding. The results are combined with electron energy-loss spectra (EELS) in a study of the electronic structure.