Influence of morphology and chemical surface composition on electrical conductivity of SiC microspheres

The present work provides a comparative study on the electrical properties (i.e. current-voltage characteristics) of spherically shaped SiC micro-sized particles that have been prepared by a thermal sintering process. As a typical field grading material, SiC exhibits a non-linear current-voltage behavior, which is exploited to reduce electrical stresses within composite materials. This is of particular interest in high-voltage applications to avoid material breakdown and to enhance the electrical components’ lifetime. As the current-voltage characteristics are affected by transport mechanisms at the grain contact, the electrical performance can be controlled by changing the chemical surface composition and morphology of the SiC particles. Advancing from irregular SiC flakes, the current work focuses on the electrical properties of SiC microspheres that have been tailored by applying selected thermal annealing steps and by chemical surface functionalization with organosilanes. The chemical surface composition of the microspheres prior to and after the modification step was studied by XPS and EDX, whilst SEM was employed to visualize the morphology of the particles’ surface and cross-section. In addition, the current-voltage characteristics were determined as a function of the particles’ morphology and chemical surface composition. The results clearly show that sintering aids, annealing temperature, morphology of particles and surface modification strongly govern the non-linear current-voltage behavior of SiC microspheres.