Corresponding States of Structural Glass Formers

The variation with respect to temperature T of transport properties of 58 fragile structural glass forming liquids (68 data sets in total) are analyzed and shown to exhibit a remarkable degree of universality. In particular, super-Arrhenius behaviors of all super-cooled liquids appear to collapse to one parabola for which there is no singular behavior at any finite temperature. This behavior is bounded by an onset temperature To above which liquid transport has a much weaker temperature dependence. A similar collapse is also demonstrated, over the smaller available range, for existing numerical simulation data.Comment: 6 pages, 2 figures. Updated References, Table Values, Submitted for Publicatio

Statistical mechanical approach to secondary processes and structural relaxation in glasses and glass formers

The interrelation of dynamic processes active on separated time-scales in glasses and viscous liquids is investigated using a model displaying two time-scale bifurcations both between fast and secondary relaxation and between secondary and structural relaxation. The study of the dynamics allows for predictions on the system relaxation above the temperature of dynamic arrest in the mean-field approximation, that are compared with the outcomes of the equations of motion directly derived within the Mode Coupling Theory (MCT) for under-cooled viscous liquids. Varying the external thermodynamic parameters a wide range of phenomenology can be represented, from a very clear separation of structural and secondary peak in the susceptibility loss to excess wing structures.Comment: 13 pages, 8 figure

Reply to Comment on “Spectral shape of the

The authors of the comment [1] criticize our recent letter [2] by three points, which we will address one by one

Glassy relaxation and excess wing in mode-coupling theory: The dynamic susceptibility of propylene carbonate above and below Tc

We explore the possibility of describing experimental susceptibility spectra of the glass former propylene carbonate with a two-component schematic model of mode-coupling theory (MCT) from above the melting point down to temperatures far below the critical temperature of MCT. By introducing a phenomenological time-dependent hopping rate, the spectra are reproduced in the full frequency and temperature range available. Literature data of dielectric susceptibilities and depolarized Brillouin light-scattering spectra are combined with our measurements of photon correlation spectroscopy to cover up to 18 decades in frequency of spectra for two different dynamical variables. A consistent description of all data sets is obtained by adjusting only a few physically motivated parameters. In particular the excess wing or slow β-relaxation commonly observed in the susceptibility spectra can consistently be modeled as originating from a coupling of the individual experimental probe correlator to the collective density fluctuations

Temperature dependence of the ionic conductivity in Li_(3x)La_(2/3-x)TiO_(3): arrhenius versus non-Arrhenius

We report on the temperature dependence of the ionic conductivity at low temperatures in the crystalline lithium ionic conductor Li_(0.18)La_(0.61)TiO_(3). Time domain measurements of the electric modulus have been performed to investigate ion dynamics in the frequency range 1025 – 102 Hz and for conductivity values in the range 10214 – 1028 S/cm. Ionic conductivity shows an Arrhenius temperature dependence below 300 K and down to 120 K, in contrast to the non-Arrhenius behavior found at higher temperatures, demonstrating that the temperature dependence of ionic conductivity in Li_(0.18)La_(0.61)TiO_(3) cannot be described by a Vogel–Fulcher–Tamman law

Slow secondary relaxation process in supercooled liquids

We report on dielectric susceptibility measurements for the glass-forming systems toluene and 1-propanol, both of which exhibit slow secondary relaxation (Johari β-process). We present a complete lineshape analysis for both α- and β-process covering the real and imaginary parts. The observation of secondary relaxation in the rigid molecule toluene shows that this process is not of intramolecular origin. The β-process is well resolved in the supercooled liquid and in the glass. Above Tg a strong temperature dependence of the relaxation strength $\Delta\varepsilon_\beta$ is observed. For the activation energy $E_\beta$ of many glass-forming systems we find the relation $E_\beta \propto T_{\rm g}$