Alternating current properties of bulk- and nanosheet-graphitic carbon nitride compacts at elevated temperatures.

The investigations of temperature-dependent electrical properties in graphitic carbon nitride (g-C 3 N 4 ) have been largely performed at/below room temperature on devices commonly fabricated by vacuum techniques, leaving the gap to further explore its behaviors at high-temperature. We reported herein the temperature dependence (400 → 35 °C) of alternating current (AC) electrical properties in bulk- and nanosheet-g-C 3 N 4 compacts simply prepared by pelletizing the powder. The bulk sample was synthesized via the direct heating of urea, and the subsequent HNO 3 -assisted thermal exfoliation yielded the nanosheet counterpart. Their thermal stability was confirmed by variable-temperature X-ray diffraction, demonstrating reversible interlayer expansion/contraction upon heating/cooling with the thermal expansion coefficient of 2.2 × 10 -5 -3.1 × 10 -5 K -1 . It is found that bulk- and nanosheet-g-C 3 N 4 were highly insulating (resistivity ρ ∼ 10 8 Ω cm unchanged with temperature), resembling layered van der Waals materials such as graphite fluoride but unlike electronically insulating oxides. Likewise, the dielectric permittivity ε ', loss tangent tan  δ , refractive index n , dielectric heating coefficient J , and attenuation coefficient α , were weakly temperature- and frequency-dependent (10 3 -10 5 Hz). The experimentally determined ε ' of bulk-g-C 3 N 4 was reasonably close to the in-plane static dielectric permittivity (8 vs. 5.1) deduced from first-principles calculation, consistent with the anisotropic structure. The nanosheet-g-C 3 N 4 exhibited a higher ε ' ∼ 15 while keeping similar tan  δ (∼0.09) compared to the bulk counterpart, demonstrating its potential as a highly insulating, stable dielectrics at elevated temperatures.