Resistivity and low frequency noise characteristics of epoxy carbon composites

The purpose of this work was to investigate resistivity and low frequency noise characteristics of composites with carbon nano particles. Investigated materials were made with different concentration of multi-walled carbon nano tubes (MWCNT) and onion like carbon (OLC) in polyurethane matrix. The carbon nanostructures, which were investigated in this work, are semiconductors. Investigations were carried out in two steps. The first step: investigations were carried out at room temperature for a wide range of voltage. The second step: investigations were carried out at fixed voltage for a wide range of temperature (75 K - 365 K). Electrical noise spectra were measured in the frequency range from 10 Hz to 20 kHz. Resistivity dependence on temperature for investigated materials is well approximated by 1/T in temperature range from 75 K to 175 K. It was shown that onion like carbon particles have larger influence on the composite conductivity comparing to MWCNTs. Electrical fluctuations of the investigated composites comprise from 1/f, 1/f^α and generation-recombination components. The largest 1/f^α noise is in the lower frequency range (up to 1000 Hz) and over all frequency range has 1/f^α character. At certain temperature recombination – generation fluctuations were observed. Noise spectral density is proportional to the square of voltage. Therefore, noise is originated from resistance fluctuations