High temperature elasticity measurements on oxides by Brillouin spectroscopy with resistive and IR laser heating

Knowledge of single crystal and aggregate elastic moduli of materials at high temperature is important in the development of high-temperature structural ceramics as well as for other areas of material sciences. Sound velocities, and hence elastic moduli, can be readily measured on micro-crystals, polycrystalline aggregates and amorphous materials using Brillouin scattering. We have developed techniques for determining the elastic moduli at high temperatures, using both electric resistive heating (to 1800 K) and CO₂ laser heating (to T > 2500 K). The full set of elastic constants of transparent oxides at high temperatures can be measured on samples with dimensions of 100 × 100 × 20 μm or even smaller. Compact resistance heaters of our design were used to study the temperature dependence of the elastic moduli of a variety of crystalline oxides and glasses, and can be used to observe high-temperature phase transitions involving elastic softening. The combination of Brillouin scattering with CO₂ laser heating allows measurements of the elastic moduli of oxides at even higher temperatures, approaching the melting points of refractory materials. The acoustic velocities of single-crystal MgO were measured to a maximum temperature exceeding 2500 ± 100 K. Both Brillouin and Raman measurements were performed on CO₂ laser-heated samples of single-crystal α-Al₂O₃ to temperatures exceeding 2000 ± 100 K. 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.