Glass transition in chlorobenzene–decalin under pressure

We have investigated the dielectric properties of a 17.2 mol % mixture of chlorobenzene and decalin in the supercooled and in the glassy state under hydrostatic pressure up to 400 MPa. The dielectric loss shows the well-known primary (α) relaxation and a secondary (β) relaxation the origin of which is still being debated. The glass transition temperature Tg increases linearly with pressure. The fragility is pressure independent. With increasing pressure the relaxation strength of the β process rises at the expense of the α process. Above around 160 K, where devitrification occurs at atmospheric pressure, the activation energy of the secondary relaxation process is roughly twice that at lower temperatures. Both energies are proportional to Tg, indicating a strong correlation between α and β processes. A possible origin of the secondary relaxation is rationalized by critical clusters in the melt.