PRESSURE-DEPENDENCE OF RAMAN MODES IN CUO

We have measured the Raman modes of CuO at room temperature for pressures up to 34 GPa. The two low-frequency modes at 298 and 345 cm-1 show linear and reversible pressure shifts of 2.7 cm-1/GPa and 2.5 cm-1/GPa. The high-frequency mode at 632 cm-1 exhibits a pronounced nonlinear frequency shift for pressures below 15 GPa and, in addition, a strong hysteresis. This hysteresis is taken as evidence for a structural instability around 10 GPa. In the low-pressure range (P < 8 GPa) the experimental data can be described by a force-constant model. Within this model the nonlinear behavior of the high-frequency mode is related to the pressure-induced change of an internal structural parameter. © 1990.