Sound velocity measurements on laser-heated MgO and Al2O3

Abstract

Brillouin spectroscopy, in conjunction with CO2 laser-heating, was employed to measure sound velocities at high temperatures on single crystals of MgO and Al2O3. The acoustic velocities of MgO were measured to a temperature exceeding 2500 (1 0 0) K, the highest temperature at which the Brillouin scattering measurements have been carried out. The temperature of MgO was inferred on the basis of independent sound velocity measurements using a resistance heater. The thermal background in the Brillouin spectra remained negligible to 1900 K and became problematic only at temperatures exceeding 2300 K. Both Brillouin and Raman measurements were performed on CO2 laser-heated samples of single-crystal α-Al2O3 to temperatures exceeding 2000 (1 0 0) K. The temperature dependence of the Raman shift was used to estimate the sample temperature. Our high-temperature velocity measurements in different crystallographic directions are in agreement with previous high-temperature elasticity measurements by resonance techniques. This demonstrates the usefulness of Raman scattering to characterize moderate temperatures (where the intensity of thermal radiation is low). Our results show that Brillouin scattering coupled with CO2 laser-heating is a viable means of performing sound velocity measurements at temperatures significantly higher than those readily made using resistance heating.