Zhu et al. acknowledged the anomalous n-type doping with Bi 3+ , which is expected to isoelectronically substitute Y 3+ . We try to confirm with defect calculations whether Bi can indeed result in n-type character. We consider Bi substitution on Y and Te sites as well as the formation of Bi interstitials. Due to the similarity in their ionic radii, octahedrally-coordinated Bi 3+ (1.03 Å) is expected to preferentially substitute Y 3+ (0.9 Å) as opposed to Te 2-(2.21 Å). In principle, isovalent Bi substitution on Y should not generate electronic carriers. Bi is known to isovalently substitute Y in bixbyite Y 2 O 3 , which has similar octahedral coordination as in Y 2 Te 3 . However, we find that the defect energetics (Figure ) are more nuanced than this simplified treatment.