RELATIONSHIP BETWEEN PARTICLE-SIZE AND MAGNETORESISTANCE IN CARBON AEROGELS PREPARED UNDER DIFFERENT CATALYST CONDITIONS

Previous studies of the temperature dependence of the high-field posit ive magnetoresistance were carried out for carbon aerogels with a fixe d [resorcinol]/[catalyst] (R/C) molar ratio of 200 but different mass densities. The present work focuses on the effect of the particle size on the transport properties of carbon aerogels of both high and low m ass densities by varying the R/C ratio within the range of 50-300, the smaller R/C ratio corresponding to smaller particle size. Correlation s of new results with SQUID and Raman findings identify the nanosize p articles to be the localization sites for transport processes. The par ticle size can be estimated from the Coulomb-gap variable-range hoppin g model, which has been successful in explaining the low-temperature m agnetoresistance data obtained for all carbon aerogels samples. The pa rticle size thus extracted is consistent with transmission electron mi croscopy measurements on the carbon aerogels and is directly correlate d with the R/C ratio. In polymeric carbon aerogels (R/C = 50), the ave rage particle size becomes comparable with the width of the glassy-car bon-like ribbons within the particles, indeed blurring the distinction between particles and inter-particle links.