states in ZnO and Sn 4d states in SnO 2 . Defect Chemistry While the electronic structure of ZnSb 2 O 6 is a promising indicator of high TCO performance, it is the defect chemistry that will ultimately control the electrical properties of the system. Degenerate conductivity is achieved when the charge carrier concentration exceeds the Mott criterion: n Mott > 0.26 a 0 3