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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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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Optical and spectral investigations confirmed the availability of phase transitions in [C 2 H 5 NH 3 ] 2 CuCl 4 at T 1 = 364 K, T h 2 = 356 K, T 3 = 232 K. It has been found that the empirical Urbach rule is fulfilled in all phases. It is shown, that in the high-temperature phases skeletal vibrations of the C±N±C group interact with phonons, whereas in the low-temperature phases internal vibrations of the metal±halogen complex occur. A ferroelastic domain structure was observed using the polarising microscope in the temperature region 232 to 364 K.

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