Low frequency light scattering in fused silica and rubidium silver iodide

We have measured the low frequency Raman spectra and the Rayleigh-Brillouin spectra of an amorphous solid,silicon dioxide, and a crystalline electrolyte, rubidium silver iodide. In fused silica the Raman spectra from 2K to 600K are independent of frequency shift from 4 to 10 cm-I• The scattering is attributed to the relaxation by thermal activation at high temperatures of the excess low frequency two-level states that are responsible for the anomalous magnitude and temperature dependence of the specific heat observed in fused silica and many other amorphous solids. The integrated intensity of the excess scattering is 10-2 times the Brillouin intensity at room temperature, consistent with the density of excess states deduced from specific heat studies. No decrease in scattering was observed in the highest temperature spectra. A double grating monochromator was used for analyzing these spectra. In RbAg I at 90C the longitudinal acoustic phonon was observed 4 5 by Brillouin scattering at a frequency shift consistent with known and measured physical properties of the crystal. The absolute intensity was determined by comparison with fused silica. The Rayleigh Ratio is 8xlO-7 cm-I and the Pockels coefficient is estimated to be 0.1. The Brillouin linewidth was instrumental and therefore less than 0.3 GHz. A triple-pass Fabry-Perot interferometer was used to analyze these spectra. The Rayleigh-Brillouin spectra of our RbAg I crystals were . 4 5 dominated by an intense Rayleigh peak of width less than 10 MHz and Rayleigh Ratio of .06 cm -1 . Removal of this feature with an iodine filter enabled us to observe a dynamic central peak wider than the 350 MHz half-width of the iodine filter. An analysis and comparison of data from an interferometer and from a double monochromator lead to the conclusion that the central peak was best fit by two Lorentzians. The broader peak has a halfwidth of 40±6 GHz and a Rayleigh Ratio of 4x10-7 cm-(one-half of the value for the Brillouin peak). The narrower peak has a halfwidth of roughly 9±3 GHz and a Rayleigh Ratio of 1 1.6xI0-6 cm-(twice the value for the Brillouin peak). The intensities and widths of these two features are consistent with the motions of mobile silver ions that dwell at a site 80% of the time and fly between sites 20% of the time.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

1978

Author dc:creator

• Field, Robert Allen

Contributors dc:contributor

• Klein, Miles V.

• low frequency light scattering
• fused silica
• rubidium silver iodide
• Raman spectroscopy
• Rayleigh-Brillouin spectra

Statement dc:rights

• 1978 Robert Allen Field

Language dc:language

en

Identifier

312045

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25090