[0001], [2-1-10] and [01-10] directions), its athermal transition to rs-ZnO and subsequent triaxial decompression of rs-ZnO to analyze the reversibility of the transition. A decrease in pressure beyond the direct transition point will not result in a reverse transition. After triaxial decompression, metastable rs-ZnO remained kinetically stable. At the same time, the excess thermal energy may allow to overcome the energy barrier between two ZnO polymorphs, while in the experiment at ambient pressure, rs-ZnO has been observed well above 300 K. In the mentioned theoretical work, it has been suggested that defects (grain boundaries) can act as potential nucleation sites, but this effect has not been studied so far. During triaxial decompression, the reverse transition was predicted to occur only upon application of a small "negative" hydrostatic pressure (about -1 GPa). It is interesting to note that the strongest preferred orientation was observed for sample #6 (recovered nanocrystalline w-ZnO, complete reverse transition): the [11-20] and [10-10] directions were preferentially aligned along the compression axis of the toroid-type apparatus. In contrast, in other samples where rs-ZnO was observed (i.e., the reverse transition was partial), the observed preferred orientation was weak or even negligible. Thus, one can assume that uniaxial decompression in the toroid-type apparatus introduces more defects and energetically favorable nucleation sites in rs-ZnO, although it is not the only reason for the activation of the reverse transition. The purity and structural defects of the grain boundaries also play an important role. Thus, the axiality of decompression seems to be the most important factor in the recovery of rs-ZnO synthesized from commercial microcrystalline w-ZnO powder.