LATTICE-DYNAMICS OF SAPPHIRE (AL2O3)

Using inelastic neutron scattering we have determined all the dispersion branches of the LAMBDA1, LAMBDA2 and LAMBDA3 representations along the three-fold axis as well as the 2 times 15 branches of SIGMA1, and SIGMA2 symmetry along the GAMMA-A-direction plus some branches along the GAMMA-D-direction. The experimental data are analyzed using various rigid ion, polarizable ion and shell models. The shell models give a very satisfactory account of the dispersion curves as well as the scattering intensities. Special attention is given to the investigation of dielectric constants and equilibrium conditions.