Phase Transitions and Stabilities among Three Phases of Di-p-tolyl Disulfides.

Di-p-tolyl disulfides (p-Tol2S2) are employed as load-carrying additives because of their anti-wear and extreme load-bearing qualities. External pressure triggers conformational up-conversion (leads to phase transition) in the molecules of p-Tol2S2, by compensating for the stress and absorbing its energy. These features make p-Tol2S2 a potential candidate for next-generation energy storage devices. Upon lithiation, MoS2 expands up to 103% which causes stress and affects battery stability and performance. Therefore, it is essential to study these materials under different physical conditions. In this work, we used density functional theory (DFT) at ωB97XD/6-31G* functional level, to calculate lattice parameters, Gibbs free energies, and vibrational spectra of three phases (i.e., α, ß, and γ) of p-Tol2S2 under different pressure and temperature conditions. The phase transition between phases α and ß occurred at a pressure and temperature of 0.65 GPa and 463 K, respectively. Furthermore, phase transition between phases α and γ was found at a pressure and temperature of 0.35 GPa and 400 K, respectively. Moreover, no phase transition was observed between phases ß and γ under the pressure range studied (0 GPa to 5.5 GPa). We also computed and compared the FT-IR spectra of the three phases. These results can guide scientists and chemists in designing more stable battery materials.