Nucleation and growth of basal-plane inversion boundaries in ZnO

Grain growth studies of zinc oxide ceramics have indicated that inversion boundaries (IBs) are growth faults that control the growth of the zinc oxide (ZnO) grains. To substantiate this observation, we designed experiments to study the nucleation of IBs. Low-temperature experiments showed that in the ZnO–SnO2 system, IBs form before the Zn2SnO4 spinel phase and grains with IBs grow exaggeratedly at the expense of the normal ZnO grains until they completely dominate the microstructure. Experiments using ZnO single crystals embedded into ZnO powder with the addition of SnO2, Sb2O3 and In2O3 showed that depending on the oxidation state of the IB-forming dopant ions, there are two competing mechanisms of IB nucleation: (i) internal diffusion, and (ii) surface nucleation and growth. The first mechanism is typical for III+ dopants and is controlled by Zn-vacancy diffusion, whereas the second mechanism holds for all IB-forming dopants and is controlled by chemisorption of the dopants on Zn-deficient (0 0 0 1) surfaces. In both cases, the driving force for the inversion is the preservation of the local charge balance.