to the high CB valley degeneracy (N v = 4) and low band effective mass m * b (0.19 m e ). In the absence of significant intervalley carrier scattering, these conditions are suitable for realizing high n-type thermopower without suppressing the electron mobility. Motivated by the predictions based on the quality factor, we perform detailed charge transport calculations within the Boltzmann transport formalism, as implemented in the AMSET package (see Computational Methods for details). A key advantage of AMSET is that it does not assume a constant relaxation time -an approximation that often leads to inaccurate predictions of charge transport properties. The electrical conductivity (σ ) and Seebeck coefficient (S) of Y 2 Te 3 , which are calculated in the temperature range 300-1200 K and electron concentrations between 10 18 -10 21 cm -3 , are presented in Figures ) and 3(b), respectively. We compare our calculated σ and S with experimental values for Bi-doped Y 2 Te 3 reported in Ref. 10. The measured σ and S for Y 2 Te 2.7 Bi 0.3 samples (denoted by circles in Figures ) lie between our calculated values at electron concentrations 10 19 and 10 20 cm -3 , suggesting that Bi-doping results in electron concentrations >10 19 cm -3 . However, n-type doping with Bi is non-intuitive because Bi is expected to isoelectronically substitute on the Y site. We performed detailed defect calculations to address this perplexity in Section 2.3.