Variable range hopping conductivity in nanocrystalline films of K0.3MoO3

We present the morphology and electrical conductivity of thin films of quasi one-dimensional conductor K0.3MoO3 produced by pulsed laser deposition. Atomic force microscopy reveals granular nature of the films with the texture depending on the substrate and deposition conditions. While the films with better texture have higher conductivity, they all show universal temperature dependence in the temperature range 20 K-300 K. The results are analyzed within the models of co-tunneling variable range hopping (VRH) conductivity in granular media based on the Efros-Shklovskii (ES-VRH) model. We suggest two different approaches to interpret the data, either by two ES-VRH regimes with crossover around 45 K or by a modified ES-VRH regime with T2 pre-factor up to T ~ 100 K and an activated one above. The second approach yields a unique value of ES-VRH parameter T0 = 1000 K in all examined films.