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.

Dielectric dispersion in ferroelectric hydrogen bonded glicyne phosphite crystal was investigated in the frequency range 100 Hz -27 GHz. Dielectric relaxation of Debye type observed in the paraelectric phase shows a critical slowing down of the polarization fluctuations. The relaxation frequency decreases with temperature according to fs = 0.305(Τ -Τ0) GHz in the paraelectric phase. The activation energy for flipping dipole motion ΔU = 2.07kΤc confirms order-disorder character of the phase transition. In the ferroelectric phase pronounced low frequency (100 Hz -1 MHz) dispersion related to domain contribution to permittivity was found.

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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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.

Electric permittivity measurments as functions of temperature at constant dc electric field and as functions of the dc electric field at constant temperatures in the paraelectric phase have been performed for DMAGaS crystal. The changes of the permittivity maximum with the electric field intensity evidence the first-order character of the ferroelectric phase transition at Tc1. The field dependence of the permittivity ε(E) in the paraelectric phase is discussed, using the classical electric equation of state. A method for the determination of the corresponding coefficients is proposed. The obtained B and C coefficients, together with double hysteresis loop observed above Tc1 prove the first-order character of the ferroelectric phase transition in DMAGaS crystal.

The paper presents the new data of dielectric dispersion in DMAGaS crystal. The very pronounced dispersion above T c1 = 136 K is observed in the frequency range 100 Ηz-30 MHz with a single relaxation process. The relaxation time τ of an electric dipole reaches 2.17 x 10 -7 s at the T, 1 . The activation free energy ΔF of the dipoles is estimated to be equal to 0.087 eV. The order-disorder type of phase transition is confirmed.

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