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

Nonlinear background corrections to dielectric permittivity of ferroics and multiferroics

Temperature measurements of dielectric permittivity are performed for nonstoichiometric ferroelectric lead germanate Pb_(4.95)Ge_3O_(11) and multiferroic solid solution [N(C_2H_5)_4]_2CoClBr_3. Unlike the heat capacity data, the analysis of the dielectric permittivity of ferroics is usually performed at the assumption that the dielectric `background' is negligible compared with its critical part. In this work we quantitatively interpret the dielectric properties of the single crystals mentioned above and the appropriate literature data for multiferroic Sr2IrO4 crystals, using generalized Curie-Weiss formulas that combine corrections due to a nonlinear temperature-dependent dielectric background, a modified critical index of electric susceptibility, and a diffuse character of phase transition. We argue that taking account of the temperature dependent dielectric background can improve notably the quantitative analysis of PTs for a number of classes of the ferroic materials

Dielectric and Dilatometric Properties of NH(CH 3

On the basis of dilatometric and dielectric investigations of NH(CH$\text{}_{3}$)$\text{}_{3}$CuCl$\text{}_{3}$·2H$\text{}_{2}$O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T$\text{}_{1}^{c}$=198 K and T$\text{}_{1}^{h}$=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$\text{}_{2}$·2H$\text{}_{2}$O 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

Dielectric and Dilatometric Properties of NH(CH3\text{}_{3})3\text{}_{3}CuCl3\text{}_{3}·2H2\text{}_{2}O Low Dimensional Ferroics

On the basis of dilatometric and dielectric investigations of NH(CH$\text{}_{3}$)$\text{}_{3}$CuCl$\text{}_{3}$·2H$\text{}_{2}$O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T$\text{}_{1}^{c}$=198 K and T$\text{}_{1}^{h}$=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$\text{}_{2}$·2H$\text{}_{2}$O 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