Raman-scattering studies of aluminum nitride at high pressure

Single crystals of aluminum nitride were studied by Raman scattering under hydrostatic pressure up to 13 GPa. Four of the six allowed modes were observed and identified. Our results under ambient conditions do not agree with already published data. The ${\mathit{A}}_1$(TO), ${\mathit{E}}_2^{\mathrm{}\left(2\right)\mathrm{}}$, and ${\mathit{E}}_1$(LO) have been followed as a function of pressure and have mode-Grüneisen coefficients of 1.58, 1.26, and 0.38, respectively. These data are compared with recent data obtained on single crystals of gallium nitride.