Fig. 8(b) shows the dependence of power factor PF on carrier concentration for un-added BTS matrix (solid line) (at 300 K). It can be seen that PF for the Sn-added specimens with f ¼ 0.1 and 0.2 wt% enhances noticeably as compared to that of un-added BTS. However, it can be seen that electron concentration for both BTS and Sn added samples does not deviate from the optimized values sub-stantially, which indicates that energy dependent scattering of electrons (as manifested by increase in λ) instead of electron concentration is responsible for the enhancement of PF of the Sn added BTS samples (f ¼0.1 and 0.2 wt%).