Aging, glass transition, supercooled and equilibrium liquid states of alkali germanate glasses studied by Brillouin scattering

The elastic properties of alkali germanate glasses, xR2O･(100 − x)GeO2 (R = Li, Na, K, Rb, Cs ; x = 14, 28), have been studied by Brillouin scattering in the wide temperature range up to 1200 °C. The remarkable aging effect of Brillouin shift ΔνL has been observed below a glass transition temperature Tg ≈ 500 °C. The temperature dependence of longitudinal sound velocity VL of well annealed glasses shows the gradual decrease below Tg, while on further heating the remarkable decrease is observed above Tg. The scaled temperature dependence of VL is nearly independent on alkali metals below the melting temperature Tm. While on further heating above Tm, the drastic decrease of VL and increase of αL show the remarkable alkali dependence. It may be attributed to the appearance of dynamic process related to ionic hopping of alkali metals released from glass network above Tm.

► Elastic properties of alkali germanate glasses at high temperatures.
► The remarkable change of sound velocity and its absorption above Tg.
► The aging effect of LA mode just below Tg.
► The observation of alkali dependence of sound absorption above Tm.