Using Rayleigh model, we study dc conductivity of the composite medium with layered inclusions. A generalized identity suitable to this kind of composite medium is proved and a definition of effective conductivity of the systems is given.
The average diameter of PbTiO3 grains is about 190nm. X-ray diffraction shows that crystal axis ratio c/a is about l at room temperature. The anoma-lies of dielectric constatnt and DC conductivity occur at about 400℃,and poling treatment rendered the pyro-electricity of PbTiO3 glass-ceramics.
High-density polyethylene (HDPE) specimens with different crystallinity have been prepared by varying annealing conditions. Based on the conventional thermally activated electronic injection process, the dependence of DC conduction on the crystallinity of HDPE has been studied.
The positron annihilation technique (PAT) is. used to determine successfully the negative single vacancy distribution in the positive and negative directions of polar axis. Our experiment verifies that the DC-conductivities of RAP crystals are caused by the thermal-defect in the crystal.
The effect of electrically pre-stressing in the composite of nano-SiOx / low-density polyethylene (LDPE) was found during measuring the high-electrical-field conduction of the composite. It means that the direct current (DC) conduction of the composite after being electrically pre-stressed with the same polarity high DC electrical stress (about 8×107 V/m) for 2h was lower than that without being pre-stressed.
It is found that the dc conductivity strongly depends on xonly for glasses with x≥ 10.
For glasses with x≤ 5, the dc conductivity is virtually composition independent.
The ac conductivity represented in these coordinates depends on xonly for glasses with x≤ 5, in which the dc conductivity does not depend on x.
In many amorphous and liquid semiconductors and other class of materials, the Meyer-Neldel rule is observed in the dc conductivity, where the preexponential factor (σ0) is found to increase exponentially with the activation energy (ΔE).
The ac conduction of most disordered materials shows a regime of constant dc conductivity σ(0) at low frequencies and a crossover to a frequency-dependent regime of the type Aωs at high frequencies.