Interface-driven dielectric relaxation and deep trap states in high-entropy spinel oxide/α-PVDF composites

In this study (Co Cr Fe Ni Mn) 3 O 4 were prepared via solid-state reaction method using five oxide precursors and was embedded in PVDF polymer matrix. Each sample has an excess of one transition element/PVDF composite film. All composite films were assessed based on the filler homogeneity using energy-dispersive X-ray spectroscopy and structurally using X-ray diffraction and Raman spectroscopy. Broadband dielectric spectroscopy and impedance analysis were performed over a wide frequency (10 -2 – 10 6 Hz) and temperature (20 – 120 °C) range to elucidate the interplay between cation chemistry, charge dynamics, and interfacial polarization. All composites exhibit pronounced frequency dispersion and thermally activated dielectric relaxation, characteristic of heterogeneous systems governed by Maxwell–Wagner–Sillars polarization and hopping-type charge transport. However, distinct and reproducible trends emerge with changing excess cation. Mn- and Fe-rich systems display strongly enhanced dielectric loss and low-frequency permittivity, consistent with polaron-assisted hopping and mixed-valence conduction. In contrast, Co-rich composites show moderated loss behavior, indicative of weaker electron–phonon coupling, while Ni-rich systems exhibit suppressed dielectric loss and delayed relaxation, reflecting stronger electronic localization and reduced carrier mobility. Cr-rich compositions primarily introduce structural disorder, modifying relaxation broadening without significantly enhancing the relative conductive loss. Impedance spectra further corroborate these findings, revealing a transition from distributed interfacial polarization at low temperatures to bulk-dominated relaxation at elevated temperatures, with cation-dependent activation of relaxation processes. Collectively, the results establish a unifying framework in which the electrical response of HEO/PVDF composites film is governed by the balance between structural disorder, electronic localization, and polaron dynamics dictated by excess transition-metal chemistry.