Spatial distribution of electrons near the Fermi level in the metallic LaB₆ through accurate X-ray charge density...

Charge densities of iso-structural metal hexaborides, a transparent metal LaB₆ and a semiconductor BaB₆, 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 LaB₆ and BaB₆ was calculated to reveal a small difference between isostructural metal and semiconductor. The weak electron lobes distributed around the inter B₆ octahedral bond were observed in the difference density. We found the electron lobes are the conductive π-electrons in LaB₆ 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.