Temperature dependences of transport properties of films, bulk samples of nanocrystals, and single crystals of niobium triselenide

The temperature dependences of transport properties of bulk samples of nanocrystals of niobium triselenide (NbSe$_3$) and films prepared from its colloid dispersions have been investigated. The results have been compared with the data for NbSe$_3$ single crystals. Changes in positions of maxima of the resistivity $\rho(T)$ at 145 and 59 K, which are associated with charge density waves (CDWs), by $\sim$ 1 K as compared to those observed for NbSe$_3$ single crystals are found for bulk samples of nanocrystals. The main contribution to resistivity $\rho(T)$ in film samples is introduced by resistance of contacts between nanocrystals, the temperature dependence of which is described by a model of the fluctuation-induced tunneling conduction. Contributions to $\sigma(T) = 1/\rho(T)$ from CDWs at a level of 10% are observed in the vicinity of temperatures of 145 and 59 K. However, in contrast to bulk samples of nanocrystals, these peaks for films not only shift downward by temperature but also broaden approximately twofold. These variations are associated with a decrease in transverse size of nanocrystallites in the films to magnitudes smaller than the CDW phase coherence length ($\sim$ 1 $\mu$m).