Enhanced Dielectric Response and Electric Field-Sensing Properties of PDMS Composites by Graphene/Nitride Heterojunctions: Insights from Experiment and DFT

Flexible dielectric composite materials capable of converting power frequency electric fields into measurable electrical signals are of great significance in the field of non-contact electric field sensing in power systems. In this paper, graphene/nitride heterojunction powders were prepared using three representative nitrides (AlN, BN, and Si3N4) and embedded in polydimethylsiloxane (PDMS) to prepare flexible composite films with a fixed filler content of 5.0 wt%. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirmed the successful formation of the heterojunctions. The results showed that the nitride-related elements (Al, Si and N) were spatially correlated with the graphene-rich regions, thus providing abundant interfacial contact sites. Dielectric spectroscopy (50 Hz–50 kHz) showed that all samples exhibited typical dispersive behavior, with the real part of the dielectric constant decreasing monotonically with increasing frequency, and the loss tangent also decreasing smoothly. Under a 50 Hz parallel-plate electric field, the normalized induced voltage amplitude (PDMS = 1) increases to 1.070 (≈7.0%) for G/PDMS, and further to 1.0723–1.07447 (≈7.23–7.45%) for AlN–G/PDMS, BN–G/PDMS, and Si3N4-G/PDMS. DFT calculations confirm that the graphene/nitride interface has a stable structure with negative binding energies (−2.241, −1.773, and −3.062 eV for AlN–G, BN–G, and Si3N4–G, respectively). Significant charge redistribution and Mulliken charge transfer (0.0538, 0.2047, and 0.0244 eV, respectively) are present at the interface, accompanied by Fermi level density of states modulation and a small bandgap opening (~0.101 eV) in BN–G. These results collectively support the interfacial polarization-driven mechanism and provide a comparative basis for selecting nitride components in graphene-based heterojunction fillers in flexible dielectric electric field-sensing layers.