Summary: | We have systematically investigated the elastic properties (<i>ρ</i>, <i>V</i><sub>P</sub>, <i>V</i><sub>S</sub>, <i>K</i>, and <i>σ</i>) of eight SiO<sub>2</sub>–TiO<sub>2</sub> glasses, varying in composition from 1.3 to 14.7 wt% TiO<sub>2</sub>, as a function of pressure up to 0.5 GPa by the pulse superposition (PSP) ultrasonic technique, and two compositions (1.3 and 9.4 wt% TiO<sub>2</sub>) up to ~5.7 GPa by Brillouin scattering in a diamond anvil cell. The parameters were also measured after annealing to 1020 °C. Composition–elasticity relationships, except for <i>K</i> and <i>σ</i>, are more or less linear; the annealing simply makes the relationships more uniform (less scatter). There is excellent agreement between the ultrasonic and Brillouin measurements at ambient and high pressure. The pressure-induced anomalous elastic behavior (negative d<i>V</i><sub>P</sub>/d<i>P</i> and d<i>K</i>/d<i>P</i>) becomes more negative (more compressible) with the increasing TiO<sub>2</sub> content. Correspondingly, the acoustic Grüneisen parameters become more negative with increases in the TiO<sub>2</sub> content, reaching a minimum near ~8–10 wt% TiO<sub>2.</sub> The comparison of the low- and high-pressure ultrasonic and Brillouin V<sub>P</sub> and V<sub>S</sub> in two glasses (1.3 and 9.4 wt% TiO<sub>2</sub>) shows excellent agreement, defining the reversible elastic behavior at low pressures and irreversible behavior at higher pressures (≥5.7 GPa) well. This result is consistent with our previous high-pressure Raman study showing an irreversible structural change in a similar pressure range.
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