Variable range hopping conduction and percolation networks in the pellets formed from pristine and boron-doped carbon nanohorn particles

Abstract

Resistivity of pelletized carbon nanohorn particles (CNHs) decreased immediately as the pressure for making the pellet increased. This behavior can be fitted by a power scaling relation with quasi-2-dimensional percolating conducting channels. Similarly, the resistivity of a pelletized boron-doped CNHs (B-CNHs) also decreased rapidly as a function of boron concentration in the region of low boron contents (<∼0.5%). On the other hand, the characteristic temperature for variable range hopping (VRH) conduction indicated different behavior, showing almost constant values for pristine CNHs and drastic changes for B-CNHs. By analyzing these experimental results using VRH theory it was found that the resistivity drop for B-CNHs can be explained by the increase of the electronic density of states at the Fermi level of nanohorns due to substitutional doping of boron in the sp2 bonded carbon network which is unlike the percolation for pristine CNHs.