The dielectric parameters and electric conductivity of (NH2(CH3)2)2CoCl4 crystals are investigated. Existence of the ferroelectric phase was observed below Tc = 258 K. The occurrence of phase transitions at 244, 314, and 435 K is confirmed. The investigated crystals also manifest anomalously high conductivity commensurate with that in semiconductors. Its value as well as region of existence strongly depend on the preceding history of the sample. It is shown that the anomalous conductivity is connected with translocation of protons which participate in the formation of hydrogen bonds.

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On the basis of dilatometric, optical, and dielectric investigations of (NH3C2H5)2CuC14 crystals the existence of phase transitions at T1 = 364 and T2 = 356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T3 = 330 K was related to earlier unknown phase transition. Besides, it was shown that these crystals are characterised by considerable protonic conductivity, the nature of which is fairly well explained in the framework of Grotthus mechanism of proton transport.

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The optical activity, birefringence and the indicatrix rotation of a (001) sample of (N(CH3)4)2ZnCl4 are measured in the high-temperature, incommensurate and partly lock-in phases with a new high-accuracy null polarimeter. The optical properties are shown to be sensitive to the annealing and X-irradiation of a sample via the defect concentration changes. The results can be explained by consideration of a modulated gyration tensor in the incommensurate phase, using the idea of modulation wave distortions imposed by defects.

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