Abstract. Polymer matrix-TiO2 composites were prepared in three different filler concentrations. The electrical relaxation dynamics as well as the electrical conductivity of all samples were examined by means of Broadband Dielectric Spectroscopy (BDS) over a wide frequency and temperature range. The recorded relaxation response includes contributions from both the polymer matrix and the reinforcing phase. Two relaxation modes (β and γ) are observed in the low temperature region, which are attributed to the re-orientation of polar side groups of the matrix and rearrangement of small parts of the polymeric chain respectively. The α-relaxation and the Maxwell-Wagner-Sillars effect (MWS), attributed to the glassrubber transition of the polymeric matrix and to interfacial polarization phenomena respectively, are observed in the high temperature region. These two mechanisms are superimposed, thus a computer simulation procedure was followed in order to distinguish them. MWS effect becomes more pronounced with increasing concentration of the filler following an Arrhenius behaviour. The relaxation frequencies corresponding to α-mode follow the Vogel-Tamann-Fulcher (VTF) equation. An additional relaxation mode is recorded at relatively high temperatures and high frequencies. Its occurrence and dynamics are related to the presence and the concentration of the filler. Finally, the Direct Current (DC) conductivity follows the VTF equation.

The threshold-electron excitation spectra of the N-heterocyclic molecules pyridine, pyridazine, pyrimidine, pyrazine, and sym-triazine have been studied with a newly constructed electron spectrometer. These are presented, discussed, and compared with photoabsorption and, whenever possible, with electron impact spectral data. Optically forbidden and n→ π* transitions have been observed. Two compound negative ion resonance (CNIR) states (``shape'' resonances) have been detected below the first excited electronic states of all N-heterocyclic molecules studied, except sym-triazine for which only one CNIR state has been observed. These CNIR states are discussed in terms of the effect of a perturbation introduced by the more electronegative nitrogen atom(s) in the benzene ring on the two lowest (degenerate) antibonding orbitals of benzene.

Dielectric impedance measurements as well as transient current–voltage (I–V) characteristics under conditions of forward and reverse bias are reported in aluminum/porous silicon (PS)∕p-cSi structures at different temperatures. Under reverse bias conditions, the electrical conduction of the structures can be modeled by a simple equivalent circuit of two parallel RC networks in series combination, representing a bulk and a junction region. The bulk conduction is ohmic. From the detailed analysis of the PS/cSi junction, the carrier concentration NA and the depletion layer width W are evaluated at each temperature. The elapsed time t0 from the onset of the square pulse, at which the transition from the dominant bulk resistance to junction conduction takes place, is a function of temperature. As the temperature decreases, conduction due to bulk resistance dominates over junction conduction. On the other, hand forward conduction is dominated from the bulk. Two conduction mechanisms are present. As the time proceeds, Poole–Frenkel conduction follows an ohmic conduction. The time after the onset of the square voltage pulse, at which this turnover takes place, is a function of temperature.

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Transient high-field electrical conduction in evaporated thin potassium iodide films has been studied as a function of the applied voltage at room temperature, covering a time range from microseconds to several hours. The results show that the universal dielectric response is valid separately in three regions. The electrical conduction is achieved through the hopping mechanism. The transition probability, associated with the hopping mechanism in each region, is affected differently by the applied voltage.