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The velocities of longitudinal and transverse ultrasonic waves in fifteen different compositions ofxLa2o3 - Geo2 - yGa2o3 glass system (x,y=0.20,0.25,0.33,0.50) were measured at room temperature using the pulse echo technique at 1OMHz and 20MHz frequencies and were measured at temperature between 25 ℃ and 350℃ with the help of an pulse echo apparatus opterating at 1OMHz frequency. The velocities data were used to determine the elastic moduli for each composition and temperature between 25 ℃ and 350℃. At room temperature, the velocities of longitudinal and transverse ultrasonic waves depend upon the composition of lanthanum gallogermanate glasses. For each composition of lanthanum gallogermanate glass, the velocities of longitudinal and transverse ultrasonic waves depend upon temperature. The velocities of longitudinal in fourth different compositions ofO.2OLa2O3-GeO2-yGa2O3 glass system were measured at various temperature using Brillioun light scattering technique. We can find the change of phase at the glass transition temperature (Tg).
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