Oxygen diffusion in single-crystal zinc oxide

The models used to describe zinc oxide-based varistors rely on diffusion and defect data obtained using techniques that have been replaced by more modern methods such as secondary ion mass spectrometry. We report values for oxygen diffusivities in undoped, single-crystal ZnO as a function of temperature and orientation. Evaporation was taken into consideration when analyzing experimental results. Within experimental error, the energetics of diffusion are isotropic, but are slightly faster in the c-direction. In comparing diffusion data from the literature, the intrinsic activation energy was estimated to be between 3.6 and 4.2 eV. Comparisons with recent theoretical calculations of relevant defect energies are discussed.