Evidence of Negative Differential Resistance in Solid Dielectrics

This paper investigates the possibility for solid dielectrics used for HVDC applications to exhibit a regime of negative differential resistance (NDR) under electric fields close or within typical operating conditions. Peculiar experimental evidence arises from space charge measurements on nano-filled polypropylene, where charge transport seems to occur in a direction that is opposite to what is normally expected. Extensive experimental investigation on space charge accumulation at different fields allowed for a rough estimation of the electric fields of NDR regime, assessed between 18 and 28 kV/mm, supporting the initial hypothesis, and possibly related to the nature of functionalized nanofillers in the material.