SYNOPSISThe ultraviolet spectra of pure and lead salt-poly(viny1 alcohol) (PVA) composite films were studied at room temperature. Blending of PVA with lead acetate and lead nitrate cause a considerable change in the UV spectrum, indicating electronic structure modifications. The complex permittivity (c*) and the complex electric modulus ( M * ) of the pure PVA and the PVA-based composite films were investigated between 300 and 400 K in the 100 Hz-100 kHz frequency range. The frequency dependence of the permittivity is influenced by the space-charge polarization. The interfacial polarization is manifested a t high temperature and becomes important only above the PVA glass transition temperature and below 1 kHz. Dielectric properties of PVA-lead nitrate composite revealed that the salt is complexed with PVA through hydrogen bonding.

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Polypyrrole samples that have been prepared in a conducting state by a chemical method using two different oxidizing agents, ferric chloride and potassium persulphate, in different concentrations have been transformed to a dielectric state by heating at 333 K for 7 days and then at 353 K for 4 days more. Then the frequency and temperature 32 dependence of the dielectric constant Ј, loss tangent tan ␦ and AC conductivity Ј were investigated using a complex impedance technique. It has been found that the concentrations of the reactants used in the preparation have a noticeable effect on the dielectric properties. It has been concluded also that heating at constant temperature has enhanced the resistivity of the samples, which can be considered as a simple method of obtaining polypyrrole (PPy) in a dielectric state rather than more complex electrochemical methods which may be useful in some future applications such as the manufacture of supercapacitors.

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The thermoelectronic power (α) of the system NiAlxFe2−xO4 and dc electrical resistivity (ϱ) are studied as a function of temperature and composition (x = 0, 0.2, 0.4, 0.6, 0.8, and 1). The single phase spinel structure is verified by X‐ray analysis. The conductivity in these compounds is explained in the light of the hopping mechanism. The results show that the resistivity increases with increasing aluminium content and the activation energy of conductivity in the paramagnetic region is higher than that in the ferrimagnetic region. The transition temperature (Tc) shifts to lower temperatures with increasing aluminium content. The thermoelectric power measurements indicated that the conductivity is due to compensation of electrons and holes. The majority of carriers are holes when the Al3+ replaces 50% of Fe3+ in the samples. The drift mobility μn for electrons is calculated at different temperatures. It increases exponentially with temperature as expected in case of ferrites and the values ranged between 10−4 and 10−6 cm2/Vs at room temperature.