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.