Brillouin light scattering of a fragile glass former: o-terphenyl

We report Brillouin scattering measurements of the fragile glass former o-terphenyl over a wide temperature range covering the normal and the supercooled liquid phase down to the glass temperature. The velocity dispersion and the absorption of the longitudinal sound waves are reported and compared with literature data. The presence of both a residual sound speed dispersion in the hot liquid phase and a strongly asymmetric shape of the Brillouin linewidth curve in the high-temperature region indicates the existence of two relaxation phenomena: a structural and a fast secondary relaxation. This picture is consistent with the classification of o-terphenyl as a non-associated liquid, as emerges from the analysis of the temperature behaviour of the ratio of the experimental to the classically calculated sound wave absorption.