Phase Transitions in the Quinol Clathrate Compounds. II. The Quinol Methanol Clathrate Compound

Low temperature heat capacities of the nonstoichiometric clathrate compounds with methanol were measured on four specimens of different occupation fractions. Heat capacity anomalies were found at 65.7. 61.0, 54.4 and 44.4 K, corresponding to the occupation fractions 0.974, 0.897, 0.837 and 0.728, respectively. Magnitude of the entropy change of transition is consistent with the view that the transition is due to randomization of direction of the methanol molecules along the c-axis. Single crystal dielectric data support this interpretation. Variation of the transition temperature with the occupation fraction was compared with data on analogous systems. The lattice energy calculation showed that the dipole interaction between methanol molecules corresponds to 27 or 67 K of temperature depending on the component of the moment taken into account.