High-Pressure Elasticity of Baltic Amber Studied by Brillouin Spectroscopy

The high-pressure elasticity of Baltic amber was investigated up to ∼12 GPa for the first time by using Brillouin spectroscopy. Two scattering geometries were adopted to derive the pressure dependence of the mode frequency of longitudinal acoustic waves, the longitudinal sound velocity, the refractive index and the density. These properties showed rapid changes at low pressures below ∼4 GPa while their changes were more sluggish at higher pressures. This crossover behavior was attributed to the collapse of free volume, which seems to be a rather common behavior of many amorphous materials. Since Baltic amber is a unique glass produced by vitrification under extremely long time, the first investigation of high-pressure elasticity reported in this study may be a good starting point for further in-depth research in this super-aged glassy system.