X-ray-diffraction determination of valence-electron density in aluminum nitride

Abstract

The valence-electron density in AlN has been measured using x-ray-diffraction intensity data. The effective charge on the nitrogen ion is somewhat dependent on the method of assessment, whether by direct integration of the electron density or by least-squares refinement of a valence population. At $\ensuremath{-}1.8(\ifmmode\pm\else\textpm\fi{}0.8)e$, it falls approximately midway between the ionic and covalent limits. The observed electron density was fitted to a bond-charge model, although clear separation of the bond charge from the valence electrons associated with the nitrogen ion proved not to be possible. In the valence-electron-density contour map the bond charge appears as a small perturbation on the essentially spherical distribution about the anion site. This is in contrast with the case of InSb, where the bond charge is quite conspicuous in the valence-electron-density map.