Research at the Laboratory of Crystallography

Orbital order in α-B₁₂ and γ-B₂₈ polymorphs of elemental boron by multipole refinements and the Maximum Entropy Method

The experimental electron density of the  α-B₁₂ allotrope of elemental boron has been obtained by the multipole refinement against low-temperature, high-resolution, single-crystal X-ray diffraction data [1]. Interpretation of the electron density with the aid of Bader analysis reveals the nature of chemical bonding in α-B₁₂. It is shown that the arrangements of bond critical points and bond paths in α-B₁₂ is indicative for orbital order of the icosahedral B₁₂ cluster, the ubiquitous building block of all polymorphs of boron and many boron-rich compounds. The previously obtained electron density of γ-B₂₈ shows that the same orbital order is visible through the peculiar curved bond paths involving the extra-cluster 2e3c bond (see case study on gamma-Boron) [2].

[1] S. Mondal, S. van Smaalen, G. Parkahonskiy, S.J. Prathapa, L. Noohinejad, E. Bykova, N. Dubrovinskaia,  Phys. Rev. B 88, 024118 (2013)
[2] S. Mondal, S. van Smaalen, A. Schönleber, Y. Filinchuk, D. Chernyshov, S.I. Simak, A.S. Mikhaylushkin, I.A. Abrikosov, E. Zarechnaya, L. Dubrovinsky, N. Dubrovinskaia, Phys. Rev. Lett. 106, 215502 (2011)