The energy and polarization characteristics of the one- and two-phonon Raman spectrum have been measured using a 180° backscattering technique. The two-phonon spectrum was measured at 20, 80, and 305°K. The one-phonon spectrum was measured at 17, 30, 80, and 305 °K. The one-phonon line of symmetry ${\Gamma }_{25}$, was shown to be Lorentzian and to have a deconvoluted half-width at 17 °K of 1.45 ± 0.05 ${\mathrm{cm}}^{-1\mathrm{}}$. The two-phonon Raman spectrum was used to determine phonon energies at the four critical points $\Gamma$, $X$, $L$, and $W$.

• Received 20 December 1971

DOI:https://doi.org/10.1103/PhysRevB.7.3685