Dielectric Dispersion Studies in (CH3\text{}_{3})2\text{}_{2}NH2\text{}_{2}Ga(SO4\text{}_{4})2\text{}_{2} - 6H2\text{}_{2}O(DMAGaS) Crystal

The paper presents the new data of dielectric dispersion in DMAGaS crystal. The very pronounced dispersion above T$\text{}_{c1}$ =136 K is observed in the frequency range 100 Hz-30 MHz with a single relaxation process. The relaxation time τ of an electric dipole reaches 2.17×10$\text{}^{-7}$ s at the T$\text{}_{c1}$. 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

Investigations of High Temperature Phase Transitions in (NH3\text{}_{3}c2\text{}_{2}H5\text{}_{5})2\text{}_{2}CuCl4\text{}_{4} Crystals

On the basis of dilatometric, optical, and dielectric investigations of (NH$\text{}_{3}$C$\text{}_{2}$H$\text{}_{5}$)$\text{}_{2}$CuCl$\text{}_{4}$ crystals the existence of phase transitions at T$\text{}_{1}$=364 and T$\text{}_{2}$=356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T$\text{}_{3}$=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

Dielectric Dispersion in Ferroelectric Glycine Phosphite

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 f$\text{}_{s}$ = 0.305(T-T$\text{}_{0}$) GHz in the paraelectric phase. The activation energy for flipping dipole motion ΔU = 2.07kT$\text{}_{c}$ 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