The intrinsic defect chemistry does not support degenerate n-type behaviour. V O acts as a deep donor defect, in line with the behaviour observed in established TCOs such as In 2 O 3 , SnO 2 and ZnO (CdO being the notable exception), and is discussed in greater detail in the SI. carriers in undoped crystals, around an order of magnitude more than predicted, and low conductivity (around 2 S/cm). The slight deviation in carrier concentration measured in the crystals is likely due to adventitious H-doping during synthesis, as well as trace amounts of other impurities that could contribute electrons (such as Cl from the carrier gas), but is in qualitative agreement with the SCFL analysis -that when nominally undoped, ZnSb 2 O 6 does not display metallic conductivity.