The AC conductivity σ(ω) and the complex dielectric permittivity ε * (ω) were studied as function of temperature 300 K < T < 600 K and at some selected frequencies (1-20 kHz) for polycrystalline sample of KClO 4 . The differential thermal analysis (DTA) thermograph was also performed. The combined data support each other and indicate the existence of a structural phase transition at ≈ 575 K. Moreover, the temperature dependence of the ac conductivity behaves in accordance with Arrhenius relation, whereas the frequency dependent conductivity obeys the power law σ(ω) = Aω s(T ) . The behavior of s with temperature suggests that the hopping over the barrier model prevails. No evidence for the existence of a ferroelectric phase transition at the transition temperature.

SYNOPSISStyrene butadiene rubber (SBR-1502) was mixed with 100 phr superreinforcing furnace ( SRF) black. The obtained rubber vulcanizate was subjected to electrical conductivity measurements at different values of tensile deformation. The log V vs. log Z graphs showed two distinct linear stages, the slope of which is nearly independent of the tensile deformation in the first stage and decreases with tensile deformation in the second stage. On the other hand, the tensile deformation was found to have an appreciable effect on the electrical conductivity. It decreases sharply as the sample is suddenly strained and then increases exponentially with time. An empirical formula describing this behavior is suggested.

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The A.C. conductivity and complex dielectric constant (relative permittivity) as function of temperature 300

A further investigation of laser-induced electrical breakdown of molecular gases is presented. By means of a modified version of the Evans and Gamal electron cascade model (1980), the breakdown parameters of molecular oxygen at pressures between 7.6*102 and 3*104 Torr irradiated with 10 ns pulse of Nd:YAG laser radiation ( lambda =1.064 mu m) are calculated. The results provide satisfactory evidence for the important role played by the attachment losses term on the breakdown phenomenon associated with the interaction of molecular oxygen with laser radiation. A study of the effect of this loss process on the electron energy distribution function and its parameters is also presented.