The relaxation processes in cellulose, methyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose were studied by dielectric spectroscopy. The dielectric spectra for these polysaccharides were measured in the frequency range from 100 Hz to 1 MHz and in the temperature range from 100 to 450 K. The dielectric relaxation data for cellulose, methyl cellulose, hydroxypropylmethyl cellulose were described by Arrhenius and Eyring equations and interpreted as due to a local motion of chain segments via the glucosidic linkages, so-calledβ-relaxation. The same relaxation process was also determined for the hydroxypropyl cellulose polymer in the temperature range of 240-270 K. At higher temperature in hydroxypropyl cellulose another relaxation mechanism occurs due to the reorientation of the side chain built of a few hydroxypropylene groups. The activation parameters of the observed dielectric relaxation processes were determined.
Electric conductivity of (Bi_{1-x}La_{x}FeO_{3})_{0.5}(PbTiO_{3})_{0.5} ceramics obtained from nanopowders synthesized by high-energy milling from respective oxides was studied in the frequency range 10 mHz ÷ 1 GHz. At room temperatures the low-frequency conductivity was found to be dominated by the contribution from poor-conducting grain boundaries, whereas the contribution in the range 1 kHz ÷ 1 MHz, due to the grain interior, was related by us to the small polaron hopping. Moreover, the electron exchange between ferric and ferrous ions activated at higher frequencies was found to be added to the conductivity above ≈ 1 MHz.
Magnetic and dielectric properties of hexagonal ferrites important for applications in microwave absorbers are strongly determined by the processing conditions. We studied dielectric and magnetic response of Sr_{1-x}Nd_{x}Fe₁₂O₁₉ (x=0, 0.03, 0.05, 0.07, 0.09) solid solutions obtained by coprecipitation method. The structure of the samples was controlled by X-ray diffraction and scanning electron microscope images revealed that the powder is a mixture of small nanograins and crystallites of 500 nm-1 μm in size. Nd³⁺ doping was found to result in an increase in the coercive field which we would like to relate to the domain wall pinning. The doping-induced changes are monotonous with x up to 0.07. The observed dispersion of permittivity was found to be correlated with the frequency behaviour of electric conductivity of the samples.
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