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We have studied the temperature dependence of conductivity, $\sigma(T)$, intwo series of Ag$_{x}$(SnO$_2$)$_{1-x}$ and Mo$_{x}$(SnO$_2$)$_{1-x}$ granularfilms lying below the percolation threshold, where $x$ is the metal volumefraction. The metal grains in the former series have approximately sphericalshape, whereas in the latter series contain numerous small substructures. Inboth series of films, we have observed the $\sigma \propto \exp[-(T_0/T)^m]$temperature dependence, with $m\,\simeq\,1/2$, over the wide $T$ range from 2to 80 (100) K, where $T_0$ is a characteristic temperature. Our $\sigma$($T$)results are explained in term of the Abeles-Sheng model which considers thestructural effect of metal grains. The extracted values of the optimalseparation between grains ($s_{m}$) and the charging energy ($E_{c}$) slightlyincrease with decreasing $x$. The variation of the parameter $C(x)$, defined inthe Abeles-Sheng model, is in consistency with a simplified expression whichdepends only on $x$ and the dielectric constant of the insulating matrix. Asthe temperature is increased to above $\sim$\,100 K, a crossover to thethermally fluctuation-induced tunneling conduction processes is observed.

Granular hopping conduction in (Ag,Mo)$_x$(SnO$_2$)$_{1-x}$ films in the dielectric regime