On the origin of unusual transport properties observed in densely packed polycrystalline CaAl₂

A possible origin of unusual temperature behavior of transport coefficients observed in densely packed polycrystalline CaAl_{2} compound [M. Ausloos et al., J. Appl. Phys. 96, 7338 (2004)] is discussed, including a power-like dependence of resistivity with $\rho \propto T^{-3/4}$ and N-like form of the thermopower. All these features are found to be in good agreement with the Shklovskii-Efros localization scenario assuming polaron-mediated hopping processes controlled by the Debye energy.