The dielectric permittivity and phase transition in the bis-(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol polymer single crystal

The temperature dependence of the dielectric permittivity ( epsilon ') of polymer single crystals of bis-(p-toluene sulphonate) or 2,4-hexadiyne-1,6-diol (PTS) has been determined for the range 140-300K. In contrast to earlier published results, the measurements along the b axis ( epsilon '/sub ///) show anomalous behaviour with a maximum of epsilon '/sub /// at Tc approximately=195K. Various models are discussed in an effort to provide an explanation for this result. A comparison is made with previous crystallographic data on the temperature evolution of the crystal structure. It is concluded that the anomalous behaviour of epsilon '/sub /// is due to a two-dimensional order-disorder-type phase transition, which occurs at about 195K. In the low-temperature phase (T Tc a slightly modified Kirkwood approach explains its decrease with temperature satisfactorily.

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