OXYGEN DIFFUSION IN SINGLE-CRYSTAL ZINC-OXIDE

The models used to describe zinc oxide-based varistors rely on diffusi on and defect data obtained using techniques that have been replaced b y more modern methods such as secondary ion mass spectrometry, We repo rt values for oxygen diffusivities in undoped, single-crystal ZnO as a function of temperature and orientation. Evaporation was taken into c onsideration when analyzing experimental results. Within experimental error, the energetics of diffusion are isotropic, but are slightly fas ter in the c-direction, In comparing diffusion data from the literatur e, 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.