Thermal and mechanical properties of rare earth aluminate and low-silica aluminosilicate optical glasses

Aluminate glasses containing 45-71.5 mol% alumina, 10-40 mol% rare earth oxide, and 0-30 mol% silica were synthesized from precursor oxides. The glass transition and crystallization temperatures were determined by differential scanning calorimetry; the structural and mechanical properties were investigated by Raman and Brillouin spectroscopy. The range of the supercooled liquid region varies from ∼40 °C to 200 °C, providing a useful working range for compositions with 5-30 mol% silica. Raman scattering showed the presence of isolated SiO4 species that strengthen the network-forming structure, enhance glass formation, and stabilize the glass even when they are present at fairly low concentrations. Sound velocities were measured by Brillouin scattering. From these and other values, various elastic moduli were calculated. The moduli increased with both aluminum and rare earth content, as did the hardness of the glasses. Young's modulus was in the range 118-169 GPa, 60-130% larger than that for pure silica glass.