Pressure Derivatives of the Elastic Constants of Vitreous Germania at 25°, −78.5°, and −195.8°C

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Abstract
The sound velocities and their pressure derivatives of vitreous GeO2 have been determined by means of a pulse superposition method at 25°, −78.5°, and −195.8°C. It was found that both longitudinal and shear velocities decrease with pressure at these temperatures. This result is qualitatively similar to that of vitreous SiO2. Although the pressure derivative of bulk modulus was positive, it was anomalously low compared with those of most other crystalline solids. The mode gamma, defined by (−d lnωi/d lnV), was calculated from the present pressure derivatives of sound velocities and was found to be temperature‐dependent. The Grüneisen parameter was estimated to be near −0.35 at very low temperatures from the mode gamma‐volume relation. This value agrees fairly well with the thermal Grüneisen parameter based on thermal data at very low temperatures.

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