Grain growth studies of ZnO ceramics indicated that inversion boundaries were the growth faults which controlled the growth of the ZnO grains. To confirm this, experiments were designed in order to investigate the nucleation of inversion boundaries. Low-temperature experiments showed that, in the ZnO–SnO2 system, inversion boundaries formed before the Zn2SnO4 spinel phase and that grains with inversion boundaries grew in an exaggerated fashion at the expense of normal ZnO grains until they completely dominated the microstructure. Experiments performed using ZnO single crystals, embedded in ZnO powder with additions of SnO2, Sb2O3 and In2O3, showed that - depending upon the oxidation state of the inversion boundary-forming dopant ion - there were 2 competing mechanisms for inversion-boundary nucleation. One of these was internal diffusion, and the other was surface nucleation and growth. The former mechanism was typical of III+ dopants, and was controlled by Zn-vacancy diffusion. The latter mechanism applied to all inversion boundary-forming dopants, and was controlled by chemisorption of the dopants on Zn-deficient (00▪1) surfaces. In both cases, the driving force for the inversion was preservation of the local charge balance.

Nucleation and Growth of Basal-Plane Inversion Boundaries in ZnO. A.Rečnik, N.Daneu, S.Bernik: Journal of the European Ceramic Society, 2007, 27[4], 1999-2008