According to our previous observations in the experiments similar to #5 but at different temperatures, the microcrystalline ZnO recovered from 7.7 GPa and ~800 K contained the traces (~3 vol.%) of rs-ZnO phase, while after increasing the synthesis temperature up to 1450-1650 K, no traces of rs-ZnO were detected. Exploring possible mechanisms. Thus, it can be concluded that both the triaxial compression and the BN environment favor the recovery of rs-ZnO. In the case of well sintered pyrolytic BN as the capsule material and the most uniform triaxial compression, 100% phase purity was achieved. Although a detailed understanding of such phenomena would require a systematic study of surface energies under extreme conditions, nucleation and growth mechanisms, as well as non-hydrostaticity and stress/strain/temperature distribution throughout the cell, some conclusions can be drawn from a simple comparison of results obtained for toroid-type and multianvil apparatuses. The main differences are as follows: