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The elastic constants of GaN have been determined using Brillouin scattering; in GPa they are: C11=390,  C33=398,  C44=105,  C66=123,  C12=145,  and   C13=106. Our values differ substantially from those quoted in the literature which were obtained from the determination of mean square displacement of atoms measured by x-ray diffraction.

A complete description of the first-order Raman and Brillouin spectra of single-crystal aluminum nitride is provided. The frequency has been measured and the symmetry identified of each of the Raman-active zone-center optic modes, and the five independent elaslic constants have been measured. The widths of the principal Raman modes increase with increasing Oxygen content up to a critical value of approximately I at.%. after which they are constant. This behavior supports the hypothesis of a change in the nature of the oxygen defect at that concentration.

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