Date of Award
Doctor of Philosophy
Materials Science and Engineering
Steve Warthen Martin
Two fully automated, temperature controlled, impedance spectroscopy workstations have been developed for this project. Impedance spectroscopy studies of glasses have been performed over the wide frequency (1 Hz-1 GHz) and wide temperature (100-500 K) range;This study yields the first-ever full compositional (three decades) range examination of the Na[subscript]2S + B[subscript]2S[subscript]3 and K[subscript]2S + B[subscript]2S[subscript]3 systems. The activation energy is modeled using a modified Anderson-Stuart model that predicts well the results for the low alkali glasses. a.c. conductivity is examined through the electrical modulus formalism and the Kohlrausch-Williams-Watts decay function. The first-ever compositional study of the approach to exponential relaxation with decreasing alkali concentration or ion-ion separation distance is reported. Although single exponential relaxation is approached, the amount of conductivity dispersion is unchanged;The first-ever study of ion dynamics through conductivity and nuclear spin lattice relaxation for three FIC lithium chalcogenide glasses (over the same frequency and temperature range are reported. For all glasses, the NSLR and the conductivity activation energies are approximately the same. The correlation time for conductivity is an order of magnitude less than that for NSLR and the KWW [beta] parameter yields smaller values for NSLR;Closer examination of the electrical modulus spectrum shows that its shape is dependent on the conductivity and the dielectric constant. The reason for the approach to single exponential behavior is due to the decreasing contribution of the hopping ions to the dielectric constant with decreasing concentration;The KWW function is not fit to the electrical modulus on the right side of the peak where the conductivity dispersion occurs and explains why conductivity dispersion is observed even for a [beta] = 0.93 fit;The ion-hopping dielectric relaxation frequency should be used as the characteristic ion-hopping frequency instead of the frequency where the M[superscript]'' peak maximum. Fitting the conductivity data with the KWW function yields [beta] values comparable to those obtained for the NSLR experiment. The similar activation energy, relaxation times and [beta] results support the hypothesis that the ion dynamics in the conductivity and the NSLR experiment are the same.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Hitendra Kumar Patel
Patel, Hitendra Kumar, "Impedance spectroscopy and NMR studies of fast ion conducting chalcogenide glasses " (1993). Retrospective Theses and Dissertations. 10850.