[en] 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. (paper)

[en] The first-order Raman spectroscopy of diamond exhibits splitting and redshift after the burst of high-pressure (160–200 GPa) and high-temperature (∼2000 K). The observed longitudinal optical (LO) and the transverse optical (TO) splitting of Raman phonon is related to the tensile-strain induced activation of the forbidden or silent Raman modes that arise in the proximity of the Brillouin zone center. (paper)