Raman spectroscopy study of ZnSe andZn0.84Fe0.16Se at high pressures

The ZnSe powder and ${\mathrm{Zn}}_{0.84}$ ${\mathrm{Fe}}_{0.16}$Se crystal were studied by Raman scattering spectroscopy at pressures up to 36.0 and 32.0 GPa, respectively. For ZnSe powder at 4.7 and 9.1 GPa, two phase transitions were observed. However, the resulted phases have not been identified yet. As the pressure was increased to 14.4 GPa, the LO phonon peak disappeared while the TO phonon peak was still visible until the metallization pressure, 17.0 GPa was reached. In addition, three unidentified Raman peaks were still observable above the metallization pressure. For ${\mathrm{Zn}}_{0.84}$ ${\mathrm{Fe}}_{0.16}$Se crystal, the structure transition from possible zinc blende to sodium chloride phase (${\mathrm{B}}_1$) was identified by the disappearance of Fe local mode and longitudinal optical (LO) phonon mode at 10.9 GPa. In addition, an unidentified phase transition at 4.7 GPa was observed. The TO phonon and the split TO phonons were still observable at a pressure above the phase transition pressure up to 32.0 GPa. The existence of Fe impurity in the ZnSe up to a concentration of 0.16 reduced the semiconductor-metal phase transition pressure to 10.9 GPa. According to the calculation of Grüneisen parameters, ${\mathrm{Zn}}_{0.84}$ ${\mathrm{Fe}}_{0.16}$ Se was found to have a higher ionicity than ZnSe. Reasons for the observation of Raman peaks at a pressure above the metallization pressure are still unknown.