Morphological effects on the transport and magnetic properties of polymeric and colloidal carbon aerogels

The temperature-dependent conductivity, magnetoresistance, magnetic susceptibility, and room-temperature Raman scattering of carbon aerogel samples with different morphologies and various grain sizes are studied. In particular, carbon aerogels with a polymeric morphology are studied and compared with colloidal carbon aerogels. The conductivity exhibits an exp[- √${\mathit{T}}_0$/T] dependence for all samples at low temperature. This strong localization behavior can be explained by a Coulomb-gap variable-range hopping mechanism, and this identification has been further corroborated by the low-temperature magnetoresistance data obtained in a magnetic field up to 15 T. Magnetic susceptibility measurements suggest that carbon aerogels with a smaller grain size are more disordered, in agreement with the conductivity data. The results suggest that the grains themselves, and not the defects within, act as carrier localization sites in these materials.