The characteristic morphology of tetrapod-shaped ZnO particles grown by oxidizing zinc vapour in air was thoroughly interpreted by a growth process from octahedral multiple-twin embryos. The origin of the tetrapod-shape arose from firstly the formation of octahedral multiple twins due to the small c/a ratio of wurtzite ZnO, secondly the presence of inversion-type twin boundaries and thirdly a large growth anisotropy with respect to the crystal polarity.

Octahedral Multiple-Twin Model of Tetrapod ZnO Crystals. Takeuchi, S., Iwanaga, H., Fujii, M.: Philosophical Magazine A, 1994, 69[6], 1125-9