Glass transition in chlorobenzene-decalin under pressure

We have investigated the dielectric properties of a 17.2 mol % mixture of c hlorobenzene and decalin in the supercooled and in the glassy state under h ydrostatic pressure up to 400 MPa. The dielectric loss shows the well-known primary (alpha) relaxation and a secondary (beta) relaxation the origin of which is still being debated. The glass transition temperature T-g increas es linearly with pressure. The fragility is pressure independent. With incr easing pressure the relaxation strength of the beta process rises at the ex pense of the alpha process. Above around 160 K, where devitrification occur s at atmospheric pressure, the activation energy of the secondary relaxatio n process is roughly twice that at lower temperatures. Both energies are pr oportional to T-g, indicating a strong correlation between alpha and beta p rocesses. A possible origin of the secondary relaxation is rationalized by critical clusters in the melt. (C) 2000 American Institute of Physics. [S00 21- 9606(00)51635-3].