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Document Type:Latin Dissertation
Language of Document:English
Record Number:52866
Doc. No:TL22820
Call number:‭3524641‬
Main Entry:Francelys A. Medina
Title & Author:Impedance spectroscopy studies of silicatitania glasses and glass-ceramicsFrancelys A. Medina
College:The Pennsylvania State University
Date:2009
Degree:Ph.D.
student score:2009
Page No:285
Abstract:Impedance spectroscopy measurements were performed on a series of silica (SiO2 ) and silica-titania (SiO2 -TiO2 ) glasses over the frequency range 40 Hz-10 MHz and the temperature range 25-700°C in order to elucidate the origin of the dielectric properties of SiO 2 -TiO2 glass-ceramics. This type of glass-ceramic was produced by controlled crystallization of a homogeneous SiO2 -TiO2 glass at the eutectic composition. This process resulted in the formation of heterogeneous structures consisting of a very large number of tiny and randomly oriented prolate spheroid crystals of high permittivity and high conductivity TiO2 , sparsely distributed in the low permittivity and low conductivity SiO2 -rich matrix. The SiO2 -TiO 2 glass-ceramics showed dielectric spectra caused by the heterogeneous microstructure. More specifically, the system exhibited a Debye-like dispersion resulting from the convolution of the interfacial polarization contributions of an even mixture of the TiO 2 spheroids having their two principal axes randomly oriented along the applied electric field. Another Debye-type dispersion results from the intrinsic dielectric relaxation of the rutile-TiO 2 inclusions. The results are in agreement with Fricke's theory for two-phase suspensions exhibiting Maxwell-Wagner interfacial polarization. To distinguish interfacial polarization relaxations due to the presence of the TiO2 particles from other possible sources of dielectric relaxations in the SiO2 -TiO2 glassceramics, the dielectric properties of various types of fused silica glasses were studied. It was found that the inherent dielectric relaxations in the SiO2 -matrix are different from those observed in the SiO2 -TiO2 glass-ceramics. These glasses exhibited one dielectric relaxation which originated at the surface of the specimens and was attributed to electrode polarization. A second dielectric relaxation at the lower frequencies originated from bulk effects and was ascribed to the conduction polarization. A novel theoretical model based on these assumptions was developed and successfully applied to the present experimental results. This model could be used to predict the effective concentration and mobility of charge carrier ions in silica glass. Impedance measurements were also carried out on glasses in the compositional series (1-x)SiO2 -xTiO2 wt% below and above the eutectic composition of ~10.5 wt% for this system. As in the case of fused silica, the observed dielectric relaxation can be described in terms of electrode polarization and conduction polarization. Above the eutectic composition, the system is phase-separated and deviations from the typical behavior in homogeneous glasses could originate from the underlying microstructure.
Subject:Pure sciences; Applied sciences; Silicatitania glasses; Glass-ceramics; Impedance spectroscopy; Dielectric properties; Condensed matter physics; Materials science; 0611:Condensed matter physics; 0794:Materials science
Added Entry:M. T. Lanagan
Added Entry:The Pennsylvania State University