The electric relaxation phenomena in nematic liquid crystals are studied using Fröhlich distribution. Different models are proposed for the relaxation of the conduction and polarization currents respectively. A statistical fitting procedure is applied to the obtained experimental data. The parameters of the relation time distribution are computed. The results are showing a very good agreement between the experimental data and the proposed models.

It is shown that by adding small percentages of nonmesogenic compounds such as anthracene, rhodamine B or S (1% by weight) in the nematic 7A, in the smectic sitosteryl undecilenate and in sitosteryl octanoate or in the Compensated cholesteric mixtures cholesteryl chloride‐cholesteryl laurate 65:35% (by weight) and cholesteryl chloride‐cholesteryl myristate 63.63:36.37% (by weight), the mixtures exhibit photovoltaic effects. These effects are obtained only for the samples which are previously polarized under dc electric fields. Using continuous ultraviolet or visible light irradiation, values of 80 to 375 mV are obtained for the open‐circuit voltage.

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It is shown that by adding potassium nitrate (I % by weight) to compensated cholesteric mixtures (cholesteryl chloride-cholesteryl myristate 63.63 : 36.37 % by weight and cholesteryl lauratecholesteryl chloride 35.65 % by weight) or to smectic sitosteryl undecilenate, the mixtures exhibit ferroelectric behaviour. Values of P, = lo-' -C/cmZ were obtained in the hightemperature range. In compensated cholesteric mixtures, the spontaneous polarisation reached a minimum at a temperature corresponding to the cholesteric-nematic transition. The results are explained by assuming coupling between the dipoles of the antiferroelectric KNO, and the dipoles of the mesogenic compound.