Chemical information from electron-energy-loss near-edge structure. Core hole effects in the beryllium and boron K-edges in rhodizite

The prospects of being able to retrieve coordination numbers of light elements (Z < 10) in solids by analyzing the fine structure of near-edge regions of electron-energy-loss peaks corresponding to excitations from core levels are examined with specific reference to boron and beryllium in the mineral rhodizite, the structure of which is already know. Proof that there are both BeO/sub 4/ and BO/sub 4/ tetrahedra in this material is obtained from the correspondence of observed and calculated spectra. Successful modeling using real-space multiple scattering calculations is achieved only if core hole effects are included by use of excited absorbing atom potentials. Various approximations to these potentials are investigated, and we conclude that the best are the (Z + 1) excited-state and (Z + 2) ion approximations. The importance of core hole effects is discussed for elements of low atomic number; and a comparison is drawn with previous work on beryllium carbide, a new calculation being performed for this solid.