A clathrate consists of both a 'host' system and a 'guest' system composed of the enclosed molecules. Treating the guest system as a diluted dipolar one, we have investigated the effects on orientational phase transitions of the cavity occupancy cursive Greek chi. a crystal field W due to host molecules, the difference between atom-atom potentials and the ignorance of those contributions by the host system which are not involved in W. It is shown that self-consistency makes the transition temperature Tc a nonlinear function of cursive Greek chi. The occurrence of a successive phase transition is shown to depend on the higher order terms of W and on the difference in the potential model. It is also clarified that the host system may affect, the estimation of Tc. We have further investigated to what extent classical statistical mechanics is applicable at low temperatures. Results are discussed in relation to the experiments.
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