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This work compares the dielectric relaxation properties of different crystalline quartz materials, according to their source (natural or synthetics). It is shown that these relaxation properties are due to a hopping process of alkaline (Li+, Na+, and K+) impurities located near [Al–O4]5- tetrahedra. A detailed analysis, in terms of the distribution function of the dielectric loss peak, allowed us to perfectly distinguish the different types of as-grown quartz. We show that (i) the natural quartz has less stable M+ charge carriers than the synthetic materials and that (ii) the homogeneity of the M+ trapping sites, created by the [Al–O4]5- tetrahedra, strongly depends on the crystal growth conditions. These features were then studied using quartz samples with different treatment conditions: as-grown, irradiated, or annealed at high temperature. We propose that the irradiation greatly facilitates the M+ relaxation, by creating additional low energy M+ hosting sites, whose number depends on the source of the quartz crystals. We also show that for 100 krad irradiation, the saturation state of the defects is already reached for all the materials under consideration. Finally, we propose that the irradiation followed by annealing at 450 °C improves the M+ stability and homogeneity in quartz materials, compared with the as-grown materials, this trend being much more relevant for the natural than for the synthetic quartz. [ABSTRACT FROM AUTHOR]

We apply a Monte Carlo technique specialized for the simulation of rare events to study the activated counterions motions in the aluminosilicate Na[sup +]-mordenite. Mean activation barriers are obtained from minimum energy paths calculated on realistic potential energy surfaces by using a Metropolis algorithm. Energy barriers for Na[sup +] hops calculated for lattices with various Si/Al ratio are found in good agreement with the Na[sup +] detrapping energies measured by thermally stimulated current spectroscopy. One shows that the dielectric activated motions of Na[sup +] proceed between degenerated many-body ground states with different dipolar moment by either sequential or collective hopping motions. This provides a first microscopic description of dielectric relaxation measured in zeolites. [ABSTRACT FROM AUTHOR]

A general statistical theory is proposed here to calculate the Gibbs energy of multicomponent mixtures. This theory is based on the assumptions of the quasichemical approximation and on the unsymmetrized self-consistent-field method. The effectiveness of the proposed theory is demonstrated through its application to determine vacancy formation parameters in rare gas solids (Ar, Kr, and Xe). In the calculations the pair potentials of Lennard-Jones and Barker et al. are used. The third-order triple-dipole forces of Axilrod–Teller–Muto are taken into consideration. The results are compared with the available theoretical calculations, Monte Carlo computations, and experimental estimations for some parameters of the vacancy formation. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Proposes a new method for analyzing the experimental results obtained from thermally stimulated depolarization current experiments on ionic conductors. Determination of energetic characteristics in solids; Presentation of a model for the thermally stimulated current spectra obtained on ionically conducting solids.

Local and non-local relaxation processes were distinguished by investigating the heating rate dependence of the thermally stimulated discharge current (TSDC) line-shape in the case of three epoxy networks of well-controlled architecture. These networks were chosen because their chain dynamics differ by the relative extent of their local and short-scale cooperative molecular motions, as a consequence of marked differences in crosslink density. As far as local motions are concerned, the TSDC evolution measured at low temperature can be accounted for by using a model based on a distribution of activation energies. On the other hand, the higher temperature part of the spectrum of the densely crosslinked network, which mainly results from cooperative motions, shows a much different behavior which cannot be fitted by such a distribution model.

Data obtained from measurements of complex impedance spectroscopy (constant sample temperature, varying electric field frequency) and dielectric dynamic thermal analysis (sample heated at a constant rate, constant electric field frequency) on Na-Mordenite (a zeolite) samples are presented and compared. Specifically, the shape and energies of the distribution of activation energies obtained from each experimental technique are compared. The two distributions are similar. However, the data obtained from dielectric dynamic thermal analysis (DDTA) seem to be in- dependent of some experimental conditions, e.g. sample geometry and the sample/electrode interface. DDTA therefore appears to be a useful technique for investigation of dielectric relaxation in ionic solids. [ABSTRACT FROM AUTHOR]