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Volume 3, Issue 2 ISSN: 2470-9905 Crystallography 2017
October 16-17, 2017
2nd International Conference on
October 16-17, 2017 | Chicago, USA Applied Crystallography
Observation of π-electron in metal hexaboride through X-ray charge density
Eiji Nishibori
University of Tsukuba, Japan
Metal hexaborides MB6, where M is an alkaline earth or rare earth metal exhibit metallic and semiconductor properties by
changing the M ion. The metal hexaborides have a B 6 octahedron in the structure. The M ion is located at the body-center
surrounded by the B6 octahedra. The B6 octahedron has 18 valence electrons. Two electrons per B6 octahedron are required to fulfill
the bonding orbital of B6 . Metal hexaborides with divalent metal ions are considered to be semiconductor and with the trivalent
ions are metal from the consideration. Theoretical study suggests that the π-electron like an anti-bonding orbital of B6 contributes
electrical conductivity in the metallic trivalent MB6. We investigated the charge densities of divalent and trivalent metal hexaborides,
semiconducting BaB6 and metallic LaB6 using the d>0.22 Å ultra-high resolution synchrotron radiation X-ray diffraction data by a
multipole refinement and a maximum entropy method. High resolution powder diffraction data were measured at SPring-8. 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 charge density. We have
successfully visualized very small amount of conductive π electrons from X-ray charge density. Electron density distribution is now
one of the most information-rich observable owing to the great improvement of experimental situation such as synchrotron X-ray
source.
Biography
Eiji Nishibori is currently a Professor of Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Japan. He has received his Bachelor's and
Master’s degree from Nagoya University, Japan. He was appointed an Assistant and Associate Professor at Nagoya University. He was then appointed as the Director of
RIGAKU-RIKEN collaboration center at SPring-8. His main research field is structural science using a synchrotron radiation X-ray including a development of experimental
and analytical system. He has received several awards including Young Scientists' Prize, the Commendation for Science and Technology by the MEXT, the CrSJ Young
Scientist Award and the Crystallographic Society of Japan.
Eiji Nishibori, Struct Chem Crystallogr Commun, 3:2
DOI: 10.21767/2470-9905-C1-002