The spectral shape of dielectric response of some solids may be described by equation. The susceptance is related to the dielectric susceptibility by a geometrical factor. Low frequency dispersion (LFD) given by the equation occurs in solids in which the dielectric response is dominated by mobile charge carriers, electrons or ions. Such a type of the dielectric response has been reported to occur in chalcogenide glasses, humid ceramics and humid zeolites. Recently thorough investigations of low-frequency dielectric properties of some low-molecular weigh organic materials has been carried out. LFD has been detected in some of them. It has been shown that LFD is connected with the injection of charge from electrodes. The measurements carried out on the annealed and irradiated samples of these materials and comparison with the results of thermally stimulated currents prove that the observed LFD is related to trapping and detrapping phenomena. Especially well developed LFD has been detected in iodized anthrone which is a charge transfer (CT) complex. The time-domain measurements on the CT complexes also show LFD behavior but the LFD is not as well developed as in the case of iodized anthrone. The results are interpreted by means of injection of charge from electrodes leading to space charge and recombination phenomena. the interpretation is a little similar to the electrochemical model of LFD proposed by Jonscher.

An improvement to the deterministic fractal interpretation of biological materials is proposed. The deterministic self- similar structure of electric circuits representing the hierarchical cellular organization in the fractal interpretation is replaced by an electric circuit of parallel R-C subcircuits with randomly distributed R and C values. We show that the so-called heavy-tailed distribution of the variate 1/(R_iC_i), representing the relaxation rate of the i-th subcircuit, is the necessary and sufficient condition for the power law behavior of the electric impedance of such a system in the high frequency range. The equivalence of the results obtained in two differently rooted approaches indicates that the variations in the local environment can provide a basis for self-similar relaxation dynamics without the need for hierarchically constrained fractal models.

The ac dielectric response of metal-insulator composites is studied numerically, using renormgroup's algorithm. For 2D and 3D random composites with bond percolation, we verify numerically that the effective dielectric function can be written numerically. A similar form has been previously verified by Bug et al. We have used a random resistor - capacitor network as a representation of a metal-insulator composite near the percolation threshold, and have calculated the scaling function using a real-space renormalization-group approach. The main idea of such approach consists of step-by-step averaging on levels of hierarchical lettice. This process is continued to fixed point of dielectric's concentration. We are finding the concentration dependencies of effective characteristics of composite material for different initial concentration of dielectric in spread range of frequencies.

The calculation of water density in the first layer of molecules in the electric field of a charged electrode is extended to hydration shells in Coulomb fields of ions in solutions. For 34 ions, the values of electric permittivity E and relative density of water in their first hydration shells, as well as the electric field strength E(approximately 10¹⁰ V/m) in the shells are given.

The dielectric relaxation spectra for several 1-bromo-n- alkanes taken from the literature have been reanalyzed in terms of the many-body theory of Dissado and Hill. Once the carbon number of the samples increases, decrease of the intercluster relaxation parameter m and increase of the intra-cluster parameter n occurs. We point out that the character of the observed dependency between the length of the molecule and the shape of the dielectric loss peak can be rationalized in terms of this theory.

The dielectric absorption spectrum between some MHz and 36 GHz has been measured at 20 degrees C for S(-)-lactic acid methylester, succinic acid dimethylester, L(-)- malic acid dimethylester and L(+)-tartaric acid diethylester, over the whole concentration range of benzene solutions of these substances. The loss function can be described by up to four Debye type spectral components. The relaxation parameters are reported and discussed in particular with respect to association effects.

A novel approach to the dielectric analysis of relaxation phenomena in glass-forming liquids is discussed. Instead of cooling, the system is polymerized so that the glass transition is approached by a chemical vitrification process. Measurements were carried out in a wide frequency interval covering 7 decades, from 10³ to 10¹⁰ Hz, on different polymerizing systems, namely two epoxy systems, the butyl acrylate and an unsaturated polyester. The relaxation function adopted for extracting the dielectric parameters is validated through a careful verification of the chemical and physical meaning of the changes observed in the dielectric susceptibility as the reaction goes on. The evolution of the shape of the relaxation function is discussed within the percolation theories developed or undercooled liquids and a satisfactory agreement between experimental results and theoretical predictions was found. The scaling behavior vs. conversion of relaxation times of both main and secondary processes closely parallels those observed in many glass-formers vs. temperature and it can well be represented by Vogel Fulcher-like Arrhenius-like equations, respectively.

The common technique of dielectric (epsilon) (t) measurements involves the application of a polarization invariant electric field to a capacitor filled with the material under study and the detection of the temporal evolution of the resulting current or charge flow. The counterpart condition of applying a given dielectric displacement and monitoring the electric field relates to the dielectric modulus M(t) with M((omega) ). Isothermal and thermally stimulated experimental techniques for directly accessing the relaxation M(t) are outlined and discussed as regards their relation to the dielectric retardation (epsilon) (t) and to dc-conductivity(sigma) _dc. We also address several microscopic processes which are inherently linked to the dielectric modulus through their common feature of displaying a redistribution of charge.

The present communication deals with the study of the (alpha) -relaxation in amorphous polymers using the technique of thermally stimulated depolarization currents. In this context, the physical significance of the so-called compensation point is discussed. Experimental results are compared with the predictions based on the hypothesis of the existence of the compensation point. It is concluded that a strong increase of the activation enthalpy is observed when the glass transition temperature is approached on heating, which is accompanied by a concomitant increase of the activation entropy. This behavior, often called compensation behavior, seems to be a real feature of the (alpha) - relaxation in amorphous polymers. Nevertheless, the compensation point seems to be an artifactual consequence of mathematical manipulation, so that its coordinates, (tau) _c, T_c, lack any physical significance and can not be related to any material property.

The dielectric loss spectrum of liquid salt solutions consists of a conductivity and a relaxational contribution, and the latter can eventually be described by distinguishable spectral components. Here the lowest frequency component is considered which is due to ionic processes. Comparing a variety of solutions it is found that the respective relaxation times are in accord with the tumbling motion of solvent shared ion pairs in some cases. In others, however, they tend to comply with an upper limit correlated to the solution viscosity in a manner which seems to indicate a relaxation mechanism of general nature.

Composite materials from polyvinylidene fluoride and ceramics barium titanate (PVDF/BaTiO₃) have been prepared. Polymer/ceramic films composites with 0-3 connectivity pattern have been produced by introducing fine grain BaTiO₃ powder in the matrix of PVDF using a well- known hot-pressure method. The addition of the ceramic powder to the polymer modifies in wide range both the dielectric and the mechanical parameters which determine the piezoelectricity of the materials. These films were polarized by the conventional technique. The results of measurements of the piezoelectric parameters and the dielectric properties of the PVDF/BaTiO₃ mixture with the various volume fraction of the components are given in this report.

The dielectric (alpha) relaxation occurring during isothermal crystallization of a glassy polymer PEKK has been recently measured in real time as crystallization proceeds. We use these new experimental data and the SchOnhals-Schlosser model to interpretation of the dielectric loss line shape of PEKK during crystallization. Once the crystallization proceeds, the values of the intramolecular diffusional hindrance parameter (alpha) , slightly decrease. Relatively fast, internal diffusion along polymer chain becomes a bit more hindered as a result of environmental change creates by crystallization process. Contrary, the intermolecular correlation parameter (kappa) is very sensitive to the crystallization process.

The dielectric response in some organic low-molecular weight compounds is defined by the injection of charge from electrodes. THe dielectric response of a few organic compounds shows a dielectric loss peak due to the relaxation of charge among traps. We can estimate the depth of traps provided that the concentration of traps is high enough. If the concentration of the injected charge is much greater than the concentration of the intrinsic charge than the depolarization consists not only on the change of the spatial distribution of charge but on the outflow of the excess charge as well. If we assume that the depolarization current is proportional to the concentration of the free charge carriers than the depolarization process may be described by the appropriate equations. The numerical solutions of the equations show that in the case of a single trapping level of the depth E_t the depolarization due to the outflow of excess charge is of Debye type. The relaxation time proves to be dependent on the concentration of traps. For the concentration smaller than 10²¹ m^-3 the relaxation time is described by equation, for the greater concentrations the relaxation time increases twice as long as for the smaller trap concentrations.

The regularities of the dark discharge in ionic contact mode as well as of the thermoelectric effect have been investigated for Zn_0.7Cd_0.3S layers. The peculiarities of electric charge formation as well as the electric voltage dependencies on poling electric field, polarization time and temperature have been analyzed in Zn_0.7Cd_0.3S layers during the present work. The mechanism of space charge accumulation have been proposed.

The method of thermally stimulate currents (TSC) is applied for electrical studies of thin film metal/insulator/metal (MIM) structures which include thin films of rare earth metal oxides (TFREMO). These structures were fabricated by vacuum deposition of MIM sandwiches on the basis of sesquioxides of ytterbium, holmium or dysprosium. The TSC thermograms for M/TFREMO/M thermoelectrects obtained at different measurement conditions were very similar. Only a single peak located at temperatures 380K-410K was observed in the experimental thermograms for the temperature range 297K-500K. The nature of the TSC peak for the examined oxides seems to be very similar. The TSC response is connected with trapping centers in TFREMO situated at energy depth of about 0.5 eV-0.7 eV.

The influence of the near contact non-uniformities in thin dielectric layers on the time-of-flight current profiles has been investigated using Monte Carlo method in systems revealing the hopping transport mechanism. In particular, the following model cases are studied: (1) enhanced or reduced hopping centers density in the near-contacts regions, and (2) wider or narrower centers distribution in energy. The simulations have been performed for various defects total concentrations, various defects distributions in energy, and various spatial extensions of the near- contact regions of enhanced/lowered centers concentrations. It has been shown that even relatively small differences in the hopping center parameters can change dramatically the measured currents, so that the overall current shape can be determined by the properties of the near-contact region. The layers with modified center distribution near only one of the contacts show remarkable polarity dependence and, in general, the near-injecting-contact region effects the current shape then the near-collecting-contact region.

The low-frequency dynamics in cereal seeds has been studied by measurements of d.c. conductivity, thermally stimulated depolarization current techniques and by broadband a.c. dielectric spectroscopy with the aim to understand its relation to their biological behavior. Such a broad overall frequency and temperature range allows to investigate simultaneously the mobility of water molecules in seeds, influence of water on molecular mobility of seeds constituents and change mobility. Our results indicate, that water in seeds freeze for concentration higher than critical hydration, whereas for lower hydration it undergoes a glass- like transition. Temperature of this transition strongly depends on water content in the sample and shifts by seeds drying from 180 K up to room temperature. D.c. protonic conductivity increases sharply above glass transition temperature. Its dependence on water content indicates percolative transport of protons along threads of hydrogen- bonded water molecules with a percolation thresholding the range of 0.15-0.30 g water/g dry material. The biological implications of these findings will be discussed.

The great interest has been shown recently in power law and universality as the properties of system formed of many interacting subunits. Among such systems are solids at 'critical points' where two or more macroscopic phases become indistinguishable. It seems that quite disparate systems behave in a remarkably similar fashion near their respective critical points - because what matters most is not the details of the microscopic interactions but rather the nature of the 'paths along which order is propagated' from one subunit to another distant subunit. These systems also exhibit power law behavior in their properties including dielectric respond on electromagnetic files. So it seems that both universality and power law reflect the fact that at critical points the interaction paths between the constituent subunits in complex systems dominate the cooperative behavior more than the detailed properties of the subunits themselves. Based on dielectric dispersion and NMR experiments this concept will be illustrated on ferroelectrics under order - disorder phase transitions.

A model is proposed in which the electric permittivity values of the macroscopic samples of the cholesteric liquid crystals can be linked to their molecular parameters. To accomplish this project, not only the transformation principles from the liquid crystal structure frame to the molecular frame should be defined, but also a method should be offered for rendering the single molecule parameters into a set of averaged quantities of the macroscopic ensemble.

Up to now only the trace and the components (alpha) ₁, (alpha) ₂ of polarizability tensor of liquid crystal sample have been investigated. The new method of (alpha) _(parallel) and (alpha) _{(perpendicular} calculation of cholesteryl nonanoate molecule was described in this work. It was determined the (alpha) _(parallel) and (alpha) _{(perpendicular}) were nonlinear functions of the temperature. It proves that cholesteryl nonanoate molecule changes its conformation. Besides, the values are always constant in all mesophase temperatures and the value of ((alpha) ₁-(alpha) ₂)(Delta) n must be also independent on the temperature.

We have observed that the temperature changes in nematic mesophases change as a result of magnetic fields. This phenomenon has been considered as a result of ordering produced by the interface and magnetic field. In this work analogous experiments carried out for three nematics compounds: PAA, MBBA, EBBA are described. The magnetic field used was B equals 0.2T. For all these compounds the temperature rises were observed, but the shape of the temperature characteristics of temperature changes was different for al the cases. We explain this phenomenon as a result of anisotropy of thermal conductivity, existing in nematics. When the magnetic field is applied to a nematic sample, the molecules are ordered along the field, so the anisotropy of the thermal conductivity takes place. In this situation the heat transport from the heater to the thermocouple was better and the temperature measured was higher. The interpretation was tested by the measurements on MBBA at the room temperature. When both the nematic sample and the heater are a the same temperature no heat generation at the magnetic field has been detected.

The most experimental methods using for determination of the order parameter in the nematic liquid crystal (NLC) require the sample to be microscopically oriented.It has been shown that the confinement of NLC to inorganic filters with regular pores provides a convenient tool for the orientation of the sample in dielectric experiments. Orientational order in the nematic phase of liquid crystal confined to Anopore membranes is measured by dielectric spectroscopy. The nematic order parameter calculated from the ratio between the dynamics of the fast and the slow processes in the 4-n- pentyl-4'-cyanobiphenyl is presented. A method for calculation of order parameter in NLC from the dielectric strengths of processes assigned to hindered rotation and tumbling about the molecular short axis is described.

It is experimentally investigated the dispersion of the dielectric permittivities in the frequency range of 1 kHz divided by 100 MHz in both nematic and isotropic phases of binary mixtures of liquid crystals with different molecular lengths. Two low-frequency relaxation processes related to the dielectric relaxation of the mixture components are separated. The relaxation times and the nematic potentials of each components are determined and compared with molecular sizes.

Measurements of ac conductivity and discharge current in P₂O₅-FeO-MO glasses were analyzed using the following procedures: (1) fitting the conductivity to the Jonscher power law, namely (sigma) _ac equals A(omega) ⁵, (2) fitting the discharge current decay to the Kohlrausch-Williams-Watt (KWW) function; (3) estimating the stretched exponent (beta) _m from the shape of the electrical modulus M^''. The parameter, (beta) , obtained from KWW approach is not substantially different if compare to the value (beta) _s equals 1-s obtained from the frequency dependence of conductivity. On the other hand a large difference is observed when compare (beta) _s with (beta) _m evaluate from the shape of electrical modulus M^''. We found that Ngai's relation W_ac equals (beta) _mW_dc is not obeyed in our glasses. The relation between activation energies W_ac, W_dc and (beta) equals 1-s is also predicted by Hunt theory. It is shown that this approach is more relevant for the interpretation of dielectric relaxation in iron phosphate glasses.

Glasses containing transition metal ions show the Jonscher 'universal dynamic response' i.e. the ac conductivity, as a function of frequency, is given by (sigma) ((omega) ) equals (sigma) (0) + (omega) ^s, where (sigma) (0) is the dc conductivity, and the exponent s (2O₅ - P₂O₅ glasses. This behavior can be described in terms of overlapping polaron tunnelling model.In the model the polaron hopping energy is reduced when polaron wells in the pair of vanadium ions do overlap. The power law of ac conductivity is observed in the high frequency range when the hopping occurs only between the nearest sites. Distances between vanadium atoms and their distributions have been evaluated from molecular dynamic (MD) simulations. The MD simulations, according to the Andersen algorithm, have been performed in the isobaric-isoenthalpic ensemble. The atoms were assumed to interact by a two-body potential, with Abrahamson parameterization. In the base of the simulation results the polaron parameters have been determined.

We have studied the influence of water absorption on properties of silica porous glasses. The thermally stimulated current technique was used for determination of electrical properties before and after heat and HMDS treatments. It was shown that thermally stimulated peaks are attributed to the polarization of water domains. Additionally, for the same specimens the IR spectra were measured.

Experimental evidence related to dielectrical response of different nematic and smectic A as well as viscous adhesives will be shown in brief. The response is quantitatively the same. There is possible to discriminate the bulk effects and electrode effects as well as AC and DC transport conductivity. Time domain technique can be also used for investigation of cross linked adhesives and solidified liquid crystalline materials. Another group of problems that can be investigated by time domain technique is the influence of electrode shape and material. The result can be compared with that of frequency domain technique. It is suggested that the time domain technique is well suited at lowest frequencies where the influence of the electrode properties are of importance. This may be of interest to those investigating material ageing phenomena. Also, reported experimental tests are of importance in respect to the use of time domain in dielectric tracking of reaction kinetics.

The relaxation processes of an epoxy resin were investigated by light scattering and broadband dielectric spectroscopy around the glass transition temperature T_g. Dielectric spectroscopy measurements give evidence of tow relaxations, a structural and a secondary one, merging into a single process well above T_g. Besides the regular divergence of the structural relaxation time, the glass transition is also evidenced by changes of the shape parameters and of the relaxation strength of the secondary process. A comparison between dielectric and Brillouin data shows that Brillouin spectra are markedly sensitive to the secondary relaxation.