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Glass structure and fluorine motion dynamics are investigated in lead-cadmium fluorgermanate glasses by means of differential scanning calorimetry, Raman scattering, x-ray absorption (EXAFS), electrical conductivity (EC), and 19F nuclear magnetic resonance (NMR) techniques. Glasses with composition 60PbGeO3-xPbF2-yCdF2 (in mol%), with x+y=40 and x=10, 20, 30, 40, are studied. Addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (Tg) and to an enhancement of the ionic conductivity properties. Raman and EXAFS data analysis suggest that metagermanate chains form the basic structural feature of these glasses. The NMR study leads to the conclusion that the F-F distances are similar to those found in pure crystalline phases. Experimental results suggest the existence of a heterogeneous glass structure at the molecular scale, which can be described by fluorine rich regions permeating the metagermanate chains. The temperature dependence of the NMR line shapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluorine mobility in these systems. [ABSTRACT FROM AUTHOR]

Continuous-wave (cw) and pulsed electron paramagnetic resonance (pulsed EPR) techniques were used to investigate spin dynamics in moderately and slightly doped poly(o-methoxyaniline), a polyaniline derivative. EPR line shapes, measured by standard cw EPR, and relaxation rates, measured by electron spin-echo methods, were studied as a function of temperature, in the ranges 6-300 K (cw) and 6-100 K (pulsed). Experimental results were explained by a model which considered two types of spins: isolated polarons in an insulating matrix, and delocalized ones in conductive islands (clusters) formed by dopant aggregates. Experimental data agreed with the assumption that EPR spectra are generated by isolated polarons coupled to the clusters by dipole-dipole interactions. Furthermore, some experimental evidence suggests that spin dynamic within the clusters, which play an essential role in the interpretation of the EPR results, is determined by exchange interactions. Consequences of the proposed model are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]