Vogel-Fulcher like dielectric response and variable range hopping behaviour in molybdenum bronze

We report on transport and dielectric properties of molybdenum bronze. Dielectric constant measurements in blue bronze samples show a low temperature anomaly exhibiting two distinct relaxational processes. One of these peaks follows a Vogel-Fulcher law and is discussed in comparison with ferroelectric relaxors. The temperature dependence of the conductivity in the ohmic regime as well as the non-linear transport properties for E-T < E < E-T(*) can be well described by a variable range hopping mechanism in both Blue and Red Bronze. We show that transport and dielectric properties are both very sensitive to the heat treatment applied to the sample. (C) 2002 Elsevier Science Ltd. All rights reserved.