Rigid covalent bond ofα-sulfur investigated via temperature-dependent EXAFS

Area of Science:

• Solid State Physics
• Materials Science
• X-ray Spectroscopy

Background:

• Alpha-sulfur (α-S) is a key allotrope of sulfur with a characteristic eight-membered ring structure.
• Understanding the temperature-dependent structural dynamics of α-S is crucial for predicting its material properties.

Purpose of the Study:

• To investigate the temperature variations in the structural parameters of α-S using Extended X-ray Absorption Fine Structure (EXAFS).
• To determine the nature of covalent bonding and interatomic potentials within the α-S structure across a temperature range.

Main Methods:

• Extended X-ray Absorption Fine Structure (EXAFS) measurements were performed at the S-K edge.
• Measurements were conducted in transmission mode using a photodiode detector across a temperature range of 10 K to 300 K.
• Data analysis involved Fourier transforms and nonlinear least squares fitting to extract structural parameters.

Main Results:

• Anomalous stability of the covalent bond within the eight-membered ring was observed, with minimal changes despite increasing temperature.
• A significant decrease in peaks related to intra- and inter-ring correlations was noted at higher temperatures.
• Structural parameters of the covalent bond showed no significant temperature variation, with a symmetric potential indicated by an asymmetric parameter (C3) of zero.
• Constant mean square relative displacement (MSRD) suggested an extremely high potential barrier for the covalent bond.

Conclusions:

• The covalent bond in α-S exhibits remarkable thermal stability, suggesting a robust and stiff structure.
• The derived Einstein temperature (942 K) and force constant (405 N m⁻¹) indicate a strong covalent bond, the strongest among chalcogen elements.
• These findings provide critical insights into the fundamental properties and potential applications of α-S.