The glassy and supercooled state of elemental sulfur: Vibrational modes, structure metastability, and polymer content

Abstract

We report a detailed investigation of vibrational modes, structure, and dynamics of elemental sulfur in the glassy and the supercooled state, using Raman scattering and ab initio calculations. Polarized Raman spectra are recorded--for sulfur quenched from 473 K--over a broad temperature range from 93 K to 273 K where the supercooled liquid crystallized. The temperature induced shifts of the majority of the vibrational modes are determined and compared with the corresponding ones of crystalline sulfur. Analysis of the reduced isotropic spectra showed that the structure of the quenched product is composed of eight member rings (S8) and polymeric chains (Sμ) with a relative fraction comparable to that of the parent liquid at 473 K. Low temperature spectra, where spectral line broadening due to thermal effects is limited, revealed that two different polymeric species are present in the glass with distinct vibrational frequencies. Their interpretation was assisted by ab initio calculations used to simulate the vibrational frequencies of polymeric chains S(8k) (k = 1, ..., 7). Theoretical results exhibit an increasing breathing mode frequency for sulfur chains up to k = 2, although it remains constant beyond the above value. The polymeric content is metastable; heating the glass above its glass transition temperature, T(g), destabilizes the chains and drives them back to the more thermodynamically stable rings. This bond interchange mechanism provides the structural origin of a secondary relaxation process in supercooled sulfur reported long ago, which has been also considered as a complication in the correct fragility estimation of this material. Finally, the Boson peak of the glass was found to exhibit strong temperature dependence even at temperatures below T(g).

The Generation of an Organic Inverted Chemical Garden

“…Raman analysis of iron(III) structures. [15] The sameconclusions can be made from analysiso fthe 1200-2000 cm À1 region (not shown). The iron(III) oleate was prepared with standard methods.…”

“…From these data, the Figure 1. [15] Furthers upport for amorphous materials is the change in the shape of the peak ( Figure 4B). B) Upward growth of Cu II in the samereactantsb ut in as olvent composed of 65 %i sopropanol and 35 %g lycerol.…”

Ultrasmall Li2S Nanoparticles Anchored in Graphene Nanosheets for High-Energy Lithium-Ion Batteries

“…Two peaks centered at 1345 and 1590 cm −1 can be respectively assigned to the D band of disordered carbon and the G band of graphitic carbon in the graphene matrix29. For the TG−S composite, two weak peaks are found at 218 and 471 cm −1 , which proves the presence of sulfur30. The Raman signals of S completely disappear after chemical reduction.…”

An Extremely High Surface Area Mesoporous-Microporous-Networked Pillared Carbon for High Stability Li-S and Intermediate Temperature Na-S Batteries

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