Experimental and Theoretical Force Constants as Meaningful Indicator for Interatomic Bonding Characteristics and the Specific Case of Elemental Antimony.

Stable Sb exhibits a rhombohedral structure, often referred to as distorted primitive cubic, with each Sb atom having three short and three longer first neighbor bonds. However, this crystal structure can also be interpreted as being layered, putting emphasis on only three short first neighbor bonds. Therefore, temperature-dependent extended X-ray absorption fine structure (EXAFS) spectroscopy is carried out at the Sb K-edge in order to obtain more detailed information on local structural and vibrational properties. Evaluation of the temperature-dependent bond lengths provides the temperature-dependent Peierls distortion while the temperature dependence of the variance of the interatomic distance distribution yields the EXAFS force constants. Ab initio density functional theory (DFT) calculations are used for determining projected force constants. Both EXAFS and DFT force constants are compared to those of other materials with different bonding characteristics, including two-center covalently bonded semiconductors, multicenter bonded IV-VI and VVI compounds, and metallic Cu. Clearly, Sb exhibits characteristics of both localized covalent bonding and delocalized multicenter bonding. This suggests a continuous transition between these two bonding scenarios and adds to the understanding of bonding in elemental Sb in particular and in IV-VI and VVI materials in general.