Atomic structure and vibrational properties of icosahedral B$_4$C boron carbide

TL;DR

This study combines experimental IR and Raman data with ab initio calculations to precisely determine the atomic structure of icosahedral B4C boron carbide, revealing the carbon atom's position and bonding characteristics.

Contribution

It unambiguously locates the carbon atom within the boron icosahedron using combined experimental and computational methods, surpassing diffraction limitations.

Findings

Carbon atom position within icosahedron determined

Intra-icosahedral bonds are harder than inter-icosahedral bonds

Provides detailed insights into vibrational properties of B4C

Abstract

The atomic structure of icosahedral B$_4$C boron carbide is determined by comparing existing infra-red absorption and Raman diffusion measurements with the predictions of accurate {\it ab initio} lattice-dynamical calculations performed for different structural models. This allows us to unambiguously determine the location of the carbon atom within the boron icosahedron, a task presently beyond X-ray and neutron diffraction ability. By examining the inter- and intra-icosahedral contributions to the stiffness we show that, contrary to recent conjectures, intra-icosahedral bonds are harder.