Hysteresis effect in pressure-induced B4-B1 phase transition of ZnO

Pressure-induced wurtzite-rocksalt (B4-B1) phase transition in ZnO has been considered a typical reversible structural transition. In the present study, the dependence of phase transition and phonon properties for ZnO has been investigated as a function of loading cycle number by in-situ high-pressure Raman scattering and micro-focus x-ray diffraction. We observed a hysteresis effect in the B4-B1 phase transition of ZnO and the importance of size reduction as cycling due to progressive breaking through first-order transition with large volume collapse (?17%). The pressure hysteresis is not a constant value, but increases with the increasing number of loading cycles. The high-pressure B1 phase can be quenchable to ambient condition after 10 compression-decompression loading cycles. Transition-induced Raman (TIR) modes at 470?630 cm(?1) associated with a local disordered structure exhibit an increase in intensity and a decrease in frequency with increasing number of loading cycles. Repeated loading phase transition cycle provides a new approach for the retainment of high-pressure phases with nano- or micro-crystalline.