In both cases, Sb is preferentially attracted towards the neutral vacancy over Zn, presumably due to the higher charge on the cation and the smaller ionic radius. The relatively equally-sized steps in inward and outward relaxation as a function of charge state in both cases stabilises the narrow formation window of V + O in ZnSb 2 O 6 , similar to what is observed in In 2 O 3 . This is different to the negative-U behaviour observed in SnO 2 and ZnO, which is driven by the much larger and non-stepwise change in bond lengths as a function of charge state. 4.668 9.265 0.504 Kikuchi et al 4.68 9.29 0.50