Abstract
In this work, electrical investigations were carried out on silica-carbon nanocomposite synthesized by sot gel technique by the incorporation of silica nanoparticles in resorcinol-formaldehyde (RF) carbon precursor solution with a masses ratio of 1. The as obtained product was dried at temperature rate of 10 degrees C/day until 150 degrees C. The samples were then pyrolysed at different temperatures between 600 and 1000 degrees C. The linearity observed in Ln(sigma) versus T-1/4 plots, for nanocomposites treated at 675 degrees C and 700 degrees C, indicates the dominance of variable range hopping (VRH) transport mechanism in these materials. Current voltage characteristics exhibit non linear and symmetric behavior for all measurement temperatures between 80 and 300 K. Therefore a negative differential resistance (NDR) phase has been detected at ambient temperature for a sample treated at 675 degrees C. For the sample pyrolysed at 700 degrees C, this non linear behavior appears for measurement temperature under 160 K. The current threshold, after which the NDR phase appears, is found to increase with an increasing sample temperature while the threshold voltage decreases. The ac conductivity was carried out for a wide range of frequencies (40 Hz-100 MHz) and measurement temperatures (80-300 K). The frequency exponent s seems to be temperature independent and close to 0.87 indicating that transport may be achieved within a quantum mechanical tunneling (QMT) model.