Spatial distribution of electrons near the Fermi level in the metallic LaB(6) through accurate X-ray charge density study

Charge densities of iso-structural metal hexaborides, a transparent metal LaB(6) and a semiconductor BaB(6), have been determined using the d > 0.22 Å ultra-high resolution synchrotron radiation X-ray diffraction data by a multipole refinement and a maximum entropy method (MEM). The quality of the experimental charge densities was evaluated by comparison with theoretical charge densities. The strong inter-octahedral and relatively weak intra-octahedral boron-boron bonds were observed in the charge densities. A difference of valence charge densities between LaB(6) and BaB(6) was calculated to reveal a small difference between isostructural metal and semiconductor. The weak electron lobes distributed around the inter B(6) octahedral bond were observed in the difference density. We found the electron lobes are the conductive π-electrons in LaB(6) from the comparison with the theoretical valence charge density. We successfully observed a spatial distribution of electrons near the Fermi level from the X-ray charge density study of the series of iso-structural solids.