ON THE HIGH-PRESSURE BEHAVIOR OF THE BOND-BENDING MODE OF AlN
Yakovenko E.V., Gauthier M., Polian A.

Received: July 8, 2003

PACS: 63.20.Dj, 64.70.Kb

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Lattice vibrations of the wurtzite-type AlN have been studied by Raman spectroscopy under high pressure up to the phase transition to the rock salt structure at 20 GPa. Five fundamental bands E₂², A₁(TO), E₁(TO), A₁(LO), and E₁(LO) have a strong, positive pressure shift, whereas the shift of the low-frequency E₂¹ band is weakly positive. We have found that the bond-bending E₂¹ mode has a positive mode Gruneisen parameter γ_i=0.04, which is qualitatively consistent with the recently reported value γ_i=0.12 [21]. Thus, we confirm that AlN remains stable with respect to the bond-bending mode, while in most tetrahedral semiconductors bond-bending modes soften on compression. Experimental results are compared with the first-principle calculations.