Raman spectra of shocked diamond single crystals

Results from time-resolved spectroscopy, used to examine the triply degenerate Raman line of diamond shocked to peak longitudinal stresses of 45 GPa in plate impact experiments, are analyzed here. The complete lifting of the degeneracy along [110] and partial lifting of the degeneracy along [100] are of particular interest. The line splittings and associated frequency shifts were analyzed using a phenomenological model based on lattice dynamics calculations. The three parameters in the model, related to the anharmonic contributions to the crystal potential, were determined unambiguously from the [110] data. Our results differ from previous values reported in the literature. Subsequent predictions of the [100] response using these model parameters are in excellent agreement with the measured results. Weighted centroids of the shifted frequencies are compared with static high-pressure measurements of the degenerate Raman line. Good agreement is demonstrated for compression to 4%, suggesting that the centroid location is not influenced by nonhydrostaticity. Nonlinear elastic stress-strain relations are presented for shock compression along different crystallographic orientations in diamond. Present analysis permits determination of diamond Raman shifts for any arbitrary deformation.