Conductive grain systems: relaxation under strong electric fields

TL;DR

This paper investigates how conductive grain systems in a dielectric matrix relax under strong electric fields, focusing on breakdown phenomena, hysteresis, and the factors influencing system failure.

Contribution

It provides a detailed description of the elementary relaxation acts and the role of electric field enhancement in breakdown and system failure.

Findings

Enhanced electric fields in gaps trigger dielectric breakdown.

Grain motions and breakdown increase composite permittivity.

System exhibits non-linear, hysteretic charge-discharge behavior.

Abstract

In an external electric field, a system of conductive grains embedded in a dielectric matrix becomes unstable and relaxes towards a conductive state. We describe and discuss the elementary acts of this relaxation. When the grains packing density is large, the relaxation is controlled by narrow gaps separating neighboring grains. The electric fields in some gaps are enhanced, relative to the external field, by the factor R/l, R being the grain radius and l the width of the gap. These enhanced fields trigger dielectric breakdown in the gaps. Both breakdown events and grain motions increase the permittivity of the composite; advancement of the breakdown process leads to global failure of insulation. The non-linear and hysteretic charge-discharge behavior of the system is determined by the main parameters characterizing the breakdown, the delay time relative to electric field increase, and the lifetime of breakdown conductivity after the supporting current has vanished.