Electrical properties of random metal-insulator composite near the percolation threshold
The electrical properties of three different systems of metal particles randomly dispersed in an insulator host near the percolation threshold were studied. The effects of the matrix phase as well as the metal-particle shape on the conductivity and dielectric properties of these random composites were investigated and compared as a function of metal-volume fraction and as a function of applied external d.c. field. Particle distribution and cluster shape, as well as the phase nature of the constituents of the composite, have been characterized by using electron microscopy (SEM, TEM, STEM), x-ray spectrum (EDS), and computer-aided image analysis. The results show an insulator-metal transition at a critical volume fraction, i.e. percolation threshold, and at a critical external field. The resistivity, dielectric constant, and dielectric loss tangent generally follow the prediction of percolation theory when metal volume fraction approaches the percolation threshold, i.e. a power-law dependence between electric properties and the distance from the percolation threshold. The critical exponents also agree with the theoretical predictions except in one case where filamentary shaped Ni particles were dispersed in polypropylene. These samples showed a deviation from the universal critical exponents predicted by the classic percolation theory. A reversible switching effect of conductivity with increasing external d.c. potential was also observed.
- Research Organization:
- Ohio State Univ., Columbus (USA)
- OSTI ID:
- 5250417
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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