A field grading composite body includes a polymeric matrix and a particulate filler distributed within the polymeric matrix. Particles of the particulate filler include a core formed from a semiconductor material, an oxide mixed layer deposited on the core, and conducting oxide layer. The conducting oxide layer deposited on the oxide mixed layer to provide an electrical percolation path through the polymeric matrix triggered by strength of an electric field extending through the field composite body. Conductors and methods of making field grading composite bodies for conductors are also described.