A Radiation-Tolerant g-C3N4 Dielectric Insulator: Local Structure Redistribution under γ-Irradiation

Abstract

Graphitic carbon nitride (g-C3N4) is a defect-rich polymeric material whose local structure is difficult to resolve using techniques dominated by average structural motifs. Here, pristine and γ-irradiated g-C3N4 samples are examined using solid-state nuclear magnetic resonance (NMR) spectroscopy. Combined 13C, 15N, and 1H NMR reveal decreased terminal −NH2 species and redistribution of interheptazine −NH– linkages with dose, while the heptazine framework remains intact. X-ray diffraction shows a non-monotonic evolution of stacking coherence, accompanied by IR evidence of C–N linkage modification. Despite these changes, the electrical resistivity remains extremely high at ∼109 Ω·cm and nearly independent of irradiation dose (10–400 kGy), temperature (RT–350 °C), and frequency (104–106 Hz). The dielectric permittivity decreases slightly from ∼7.2 to ∼4.7–5.2, while the dielectric loss tangent remains low (∼0.02). The refractive index similarly decreases from ∼2.6 in pristine g-C3N4 to ∼2.2–2.3 after γ-irradiation. Analysis of the frequency dependence follows the universal dielectric response, consistent with correlated barrier hopping conduction with predominantly three-dimensional charge transport. Together, these observations show that γ-irradiation primarily reorganizes linkage environments without significantly perturbing the π-conjugated heptazine framework that governs charge transport. These characteristics make γ-irradiated g-C3N4 promising for radiation-resistant dielectric and insulating components in nuclear and high-radiation electronic environments.