Berlin 2005 – scientific programme
Parts | Days | Selection | Search | Downloads | Help
DF: Dielektrische Festkörper
DF 7: Gl
äser I (gemeinsam mit FV DY)
DF 7.10: Talk
Monday, March 7, 2005, 12:30–12:45, TU A060
Low temperature dielectric properties of molecular glasses — •Catalin Gainaru1, A. Rivera1, E.A. Rössler1, and G. Eska2 — 1Physikalisches Institut Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany — 2Physikalisches Institut Experimentalphysik V, Universität Bayreuth, 95440 Bayreuth, Germany
We present a systematic study of the dielectric response of simple molecular glass formers below the glass transition temperature Tg down to 4K. The investigations were carried out by applying the new Andeen Hagerling ultra-precision capacitance bridge (resolution tanδ∼10−6, 50Hz - 20kHz). For systems showing no secondary relaxation peak ("type A") a nearly constant loss with an exponential temperature dependence prevails below Tg while for the other systems ("type B") the fluctuations are dominated by the β-process. Though the dynamics can be well distinguished between "type A" and "type B" systems down to 50 - 70 K, below the classification becomes meaningless: for all the investigated systems a crossover to another relaxation phenomena is found. For some systems the dynamics can be described by thermally activated transitions in asymmetric double well potentials. For others this model does not apply. Nevertheless, at temperatures below 10 K, an universal weak frequency dependence similar to the one for inorganic glasses is found for all the systems indicative of the tunneling regime.