ZnO-Modified Gd ₂ FeCrO ₆ Nanocomposites with Tunable Polaron Transport for High-Performance Dielectric Energy Storage

Engineering dielectric interfaces in perovskite oxides offers a promising pathway toward high-performance energy storage materials. Here, ZnO-modified Gd 2 FeCrO 6 double perovskite composites are developed to regulate defect-mediated polarization and interfacial charge transport. Structural and microstructural analyses reveal preserved phase stability with pronounced ZnO-induced grain refinement, generating heterogeneous interfaces that strongly influence the dielectric response. The optimized Gd 2 FeCrO 6 @1 wt % ZnO composite exhibits a significant enhancement in dielectric permittivity, increasing nearly fivefold compared to pristine Gd 2 FeCrO 6 and continuously increasing with temperature up to 95 °C while maintaining low dielectric loss. Impedance spectroscopy indicates thermally activated small-polaron hopping coupled with strong Maxwell–Wagner interfacial polarization, with nearly identical activation energies for grain (0.20 eV) and grain-boundary (0.21 eV) conduction, suggesting coupled relaxation processes. Ferroelectric P – E measurements reveal that pristine Gd 2 FeCrO 6 exhibits slim, nearly linear loops with low recoverable energy density (∼110 J/m 3 ) and moderate efficiency (∼73%), whereas the Gd 2 FeCrO 6 @1 wt % ZnO composite displays slimmer, well-defined loops with enhanced polarization reversibility, yielding a higher energy density (∼440 J/m 3 ) and improved efficiency (∼94.1%). These results establish ZnO-induced interface engineering as an effective approach to modulate charge dynamics and dielectric polarization in double perovskite systems, offering promising prospects for solid-state capacitive energy storage applications.