Carbon-vanadium nanocomposites were prepared by sol–gel route after incorporating vanadium pentoxide nanopowder in carbon matrix based on resorcinol–formaldehyde xerogel, followed by thermal treatment. The resulting samples were characterized by different techniques, namely X-ray diffraction, Fourier transform infrared spectroscopy, RAMAN spectroscopy, Scanning electron microscopy, and electrical analysis. The X-ray diffraction analysis carried out on our samples that exhibits the pyrolysis temperature brings out the crystal phase change from V2O5 phase to V2O3 phase, also the presence of graphite phase in the samples, and the appearance of vanadium carbide V8C7 phase in sample pyrolyzed at 1000 °C. The Fourier transform infraredspectra are characterized by the appearance of peaks at 997, 792, and 559 cm−1corresponding to V–O stretching modes. RAMAN analysis shows the presence of characteristic peaks of vanadium oxide and the D and G bands characteristic of graphite. The Scanning electron microscopy graphs indicate the presence of macroporous carbon enriched by vanadium oxide in nanofibres shape. In addition, in an interesting way, the obtained material presents a percolation phenomenon in the temperature zone from 600 to 800 °C where the behavior of the material changes from insulator state to conductor one as a function of pyrolysis temperature. For that, the electrical analyses were carried out for the sample prepared at 650 °C. The dc conductance indicates a thermally activated process. The ac conductance shows a semiconductor–metal behavior change at 200 K. Indeed, the transfer of charge carriers is dominated by the correlated barrier hopping conduction model in the prepared material for measurement temperatures below 200 K. The impedance analysis shows a non-Debye relaxation phenomenon in the system. An electrical equivalent circuit has been proposed for the analysis of the impedance results and the determination of the fundamental parameters of the circuit at different measurement temperatures to estimate the contributions of the grains to the conductivity.

This work was financially supported by the Tunisian Ministry of Higher Education and Scientific Research through the budget of the Tunisian Laboratories.

Peer reviewed