Raman linewidths of optical phonons in 3C-SiC under pressure:: First-principles calculations and experimental results

We have studied the pressure dependence of the linewidths of the longitudinal and transverse optical phonons at the Brillouin-zone center in 3 C-SiC. Raman measurements at 6 K, which cover the pressure range up to 15 GPa, are in good agreement with first-principles calculations also reported here. These results differ considerably from previous experimental data. While the linewidth of the transverse mode remains practically unchanged within our pressure range (up to 35 GPa for the calculation), that of the longitudinal mode shows a monotonic increase up to 26 GPa, decreasing abruptly above this pressure. The mechanisms responsible for this anomalous behavior are identified and discussed. Experimental and theoretical results concerning the pressure dependence of phonon frequencies and related quantities complete the work. [S0163-1829(99)02409-1].