Low-temperature glassy features in crystal phase of pentamethylchlorobenzene, PMCB

The translational and orientational disorder of some liquids can be frozen if they are cooled down quick enough, giving rise to a Structural Glass (SG). Many features commonly exhibited by canonical glass-formers are also observed in systems that exhibit long-range translational order while retaining orientational disorder – such as in plastic crystals. Examples include the monoclinic low-temperature phase of CBrnCl4-n molecules (n = 0,1,2), certain adamantane derivatives, and some benzene derivatives. In all these cases, the disorder arises from the occupancy of different molecular sites by specific atoms. We propose to perform INS measurements at 5 K on low-temperature solid phase of the benzene derivative pentamethylchlorobenzene using the MARI instrument. The goal is to study the vibrational properties in the low-energy region. These measurements will be supported by ab-initio DFT lattice dynamics calculations and AIMD simulation to aid the interpretation of the experimental S(ω) spectra.