Where is the electronic glue in aluminium?

A new approach to QCBED has allowed the metallic bond in aluminium to be characterised unequivocally for the first time in over 80 years of experimental and theoretical investigation. This knowledge is essential to understanding the role of interatomic bonding in stabilising atomic scale strengthening precipitates in alloys. This information will not only aid structure determination of strengthening precipitates in commercial aluminium alloys, but will also contribute to a deeper understanding of the evolution of commercial alloys as they are processed. Angular-difference QCBED has measured the electron density in aluminium with up to a ∼20-fold improvement in uncertainties over all previous X-ray diffraction measurements. This high precision was crucial in establishing that the bonding electrons are located exclusively in the tetrahedral interstices of the fcc structure. These measurements were also of sufficient precision and accuracy to allow the anisotropic mechanical properties of aluminium to be equated accurately to bonding potential and electron density. These measurements have also allowed a first-principles solid-state DFT to be benchmarked and identified as predicting the correct electronic structure for aluminium. Electron density is the fundamental basis for first principles solid-state theory and armed with an experimentally verified theory, one can predict the behaviour of more complex aluminium-based systems (alloys) with new levels of confidence.