We present novel low-frequency (0.1 Hz-50 Hz) measurements of the complex elastic susceptibility of the glass-forming liquid salol confined to nanoporous Vycor glass. Our data can be perfectly interpreted with the assumption of a radial distribution of Vogel-Fulcher temperatures T0(r) inside the pores, resulting from an increase of the molecular relaxation time with decreasing distance from the rough pore surface as recently found by computer simulations (Scheidler et al., Europhys. Lett. 59, 701 (2002)). The results show for the first time, that the dynamic elastic response is extremely sensitive for separating confinement-induced acceleration effects of the molecular dynamics and surface-induced slowing-down due to rough pore interfaces.
The temperature- and frequency-dependent dielectric susceptibility parallel to the ferroelectric axis of crystals was studied in the ferroelectric phase. The dispersion corresponding to a critical slowing down of the thermal dipole relaxation was observed in the vicinity of in the frequency range 1 - 10 MHz. Besides, a dispersion which is related to the dipole reversal within the domain walls was found at lower frequencies. The latter is much more pronounced in the deuterated sample and is thought to be connected with the dynamics of hydrogen bonds.
We have studied the frequency and temperature dependence of the dielectric constant parallel to the ferroelectric c axis in the ferroelectric phase of KH2AsO4. The dielectric dispersion found in the high-frequency range (1 MHz-1000 MHz) could be described by a Vogel-Fulcher-dependent Gaussian distribution of relaxation times, similarly as in KH2PO4. However, the use of a Vogel-Fulcher law is less convincing than in KH2PO4. Below the freezing temperature Tf the relaxation times strongly increase resulting in a decrease of the domain wall mobility. This may be due to the non-linear superposition of the piezoelectric resonance and the relaxational dispersion.
Dielectric and dilatometric investigations of (NH2(CH3)2)2CoCl4 crystals were performed in the temperature range 290 to 430 K. Anomalies characteristic of phase transitions have been found at the temperatures 419, 380, 353, and 313 K (in a heating run). In certain phases the investigated crystal shows anomalously high protonic conductivity and dielectric permittivity which strongly depend on the influence of extrinsic water. The phenomenon clearly manifests itself by the appearance of new features in Cole‐Cole diagrams.
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