which is proved to be caused mainly by changes of carrierconcentration. In contrast, Seebeck coefficient S for the nanocomposites increases monotonicallywith increase in f, specially at T < 380 K, suggesting that at low a-SiO2 (f ¼ 0.55 vol. %) content,at least, the increase in S of the nanocomposite could be ascribed to energy filtering effect arisingfrom enhanced carrier scattering by the interface potentials due to the embedded a-SiO2nanoparticles.