Effect of the Pyrolysis Temperature on the Negative Differential Resistance in Carbon/Vanadium Nanocomposite

Organic-inorganic nanocomposites (RF/VOX) based on resorcinol-formaldehyde carbon matrix enriched by vanadium nanoparticles were synthesized by sol-gel method coupled with pyrolysis treatment. The crystallite structure of the resulting sample was investigated by X-ray diffraction technique, which shows the change of the V₂O₅ phase to V₂O₃ one under the pyrolysis temperature effect and the presence of vanadium carbide V₈C₇ phase in sample pyrolyzed at 1000 °C. The X-ray diffraction analysis proves the appearance of the graphite phase in all samples. Microscopic images (transmission electron microscopy and scanning electron microscopy) indicate the presence of macroporous carbon enriched with vanadium oxide in the form of nanobelts. These structural observations strongly affect the electrical properties. The current-voltage curves exhibit the presence of non-linear behavior for samples RF/VOX-625 and RF/VOX-650 which is identified as negative differential resistance NDR phenomenon. This NDR behavior appears at applied voltages of 51 and 180 V for samples RF/VOX-625 and RF/VOX-650, respectively. The Joule heating effect and filament formation were estimated as the origin of NDR behavior. The conductivity of our samples can be modulated by applying current. The coexistence of these two behaviors makes our samples promising for threshold switching and oscillator circuits.