  We present a study of the temperature (T) dependence of the dc electrical
conductivity of polyaniline pellets doped over a wide range. A crossover
between low-T variable-range hopping and high-T nearest-neighbor hopping has
been found below room temperature for most of the samples, which is atypical
for conducting polymers. This allows us to construct an experimental diagram
that accounts for different regimes in the hopping electron transport and
closely resembles predictions of the Fogler-Teber-Shklovskii model in three
dimensions.
