Our results show that Bi doping still maintains the n-type character due to donor Y i , in agreement with the n-type character of Bi-doped Y 2 Te 3 observed experimentally. However, it is also observed experimentally that increasing the nominal Bi concentration reduces the n-type Seebeck coefficient and electrical resistivity, suggesting an increase in the electron concentration. This anomalous effect cannot be explained by a simple site substitution doping mechanism. The Bi-doped Y 2 Te 3 samples by Zhu et al. were prepared with high (nominal) concentrations of Bi, which is beyond the dilute doping limit (typically < 1%). Therefore, one plausible explanation for the observed n-type character of Bi-doped Y 2 Te 3 is that Bi substitution significantly alters the electronic dispersion of both the conduction and valence band edges through substitution on the Y and Te sites, respectively, as the CB and VB edges are primarily composed of Y-d and Te-p or-bitals, respectively (Figure ). In particular, the perturbation of the CB edge may induce convergence of the multiple low-lying valleys (Figure ). Secondly, Bi incorporation may form an alloy (rather than a material with dilute doping) with native defect energetics that are different from the undoped Y 2 Te 3 . Finally, unintentional doping may also lead to confusing results. For example, unintentional H incorporation is responsible for the persistent ntype character of wurtzite ZnO and prevent p-type doping. We therefore attribute the n-type character of Bi-doped Y 2 Te 3 to either a change in the defect energetics combined with a change in the band edge dispersion or unintentional n-type doping not directly related to Bi.