The thermal expansion of single-crystalline ${\mathrm{C}}_6$ is studied using high-resolution capacitance dilatometry. In addition to the orientational-ordering transition at 261 K, we observe a transition at ${\mathit{T}}_{\mathit{g}}$≊90 K due to the freezing in of orientational disorder, which has the character of a glass transition. The relaxation near ${\mathit{T}}_{\mathit{g}}$ is studied by varying the heating (cooling) rate over more than two decades. It is found to obey an Arrhenius behavior with ${\mathit{E}}_{\mathit{a}}$=288±5 meV within a simple glass-transition model.

• Received 27 August 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.3774