Raman Modes of6HPolytype of Silicon Carbide to Ultrahigh Pressures: A Comparison with Silicon and Diamond

We report the Raman study on $6H$-SiC to ultrahigh pressure of 95 GPa in a diamond anvil cell. The $\mathrm{LO}\left(\Gamma \right)$ and $\mathrm{TO}\left(\Gamma \right)$ Raman frequencies increase with increasing pressures. A very interesting turnaround in the LO-TO splitting is observed above 60 GPa. The density variation of the mode Grüneisen parameters for $6H$-SiC is compared to that of silicon, cubic boron nitride, and diamond. The SiC is transparent to the visible light at 95 GPa and the anticipated metallic phase was not observed.