On the basis of dilatometric, optical, and dielectric investigations of (NH_{3}C_{2}H_{5})_{2}CuCl_{4} crystals the existence of phase transitions at T_{1}=364 and T_{2}=356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T_{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.
The dielectric study of Sr_{0.73}Ba_{0.27}Nb_2O_6:Ce (SBN) crystals along [010] crystallographic axis was performed in the temperature region of 310-360 K and frequency range from 25 Hz up to 1 MHz. The thermal dipole relaxation of quasi-Debye-type for this orientation of sample was observed in both investigated structural phases. The phase transition was most clearly seen from the temperature dependence of the relaxation time at T_{c} = 320 K. The relaxation processes were related to the collective oscillations of the Nb-O bonds in the two different type corner-sharing NbO_6 octahedra aligned along c-axis.
This paper presents the results of investigations of the radiation effects in NH_2(CH_3)_2Al(SO_4)_2×6H_2O crystals doped with chromium. On the basis of absorption spectroscopy and resonance Raman scattering study it has been shown that comparatively low doses of radiation first of all causes recharging of Cr^{3+} on Cr^{4+} ions. Besides, the processes of dehydrogenation and the changes in arrangement of the hydrogen bond network were observed. These changes are followed by distortion of the complexes bonded by such a type of bonds.
On the basis of dilatometric and dielectric investigations of NH(CH_3)_3CuCl_3·2H_2O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T_1^c=198 K and T_1^h=223 K, respectively, in cooling and heating runs. Existence of the characteristic dielectric dispersion was revealed within the high-temperature phase. It corresponds to the single dielectric relaxator below 250 K as well as to co-existence of two relaxators above this temperature. The determined values of the activation energy and relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation (high-frequency relaxator) whereas the combined reorientation motions of the CuCl_2·2H_2O chains would be responsible for the low-frequency relaxation process. It was found that the above mentioned quasi-Debye type processes are involved into the mechanisms of the protonic conductivity.
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