Abstract
Raman-scattering experiments on heavily irradiated pure and doped NaCl crystals are described. The experiments have been performed at room temperature and at approximately 25 K. The crystals had been irradiated up to a maximum dose of 95 Grad by means of electrons from a Van de Graaff accelerator. The Raman spectra show the set of phonon peaks corresponding to the NaCl modes. At low frequencies the reduced Raman intensity shows a clear power-law dependence on the frequency, (ω)∝, with an exponent ν≃1.4, indicating that the colloids in heavily irradiated samples exhibit a fractal structure. The change in the melting peak pattern reveals that the initial form of the sodium particles is strongly affected by the performance of a Raman experiment at room temperature. At low measuring temperatures two unknown phonon peaks at 330 and 560 are observed. These peaks are located well above the phonon cutoff frequency of NaCl at 260 , and are associated with local modes due to the ultrafine structure of the colloids.
- Received 2 March 1994
DOI:https://doi.org/10.1103/PhysRevB.50.9798
©1994 American Physical Society