Optical and Dielectric Properties of Sr(x)Ba(1-x)Nb(2)O(6)

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Title: Optical and Dielectric Properties of Sr(x)Ba(1-x)Nb(2)O(6)
Authors: David, Calin Adrian
Thesis advisor: apl. Prof. Dr. Manfred W√∂hlecke
Thesis referee: Jun.-Prof. Dr. Mirco Imlau
Abstract: Several SBN-x crystals of different composition have been investigated using the following methods: Optical absorption in the band gap spectral region, optical absorption of the OH-stretch-mode in the near infrared, Raman scattering, pyroelectric and dielectric measurements.The band edge position depends on the crystal composition in a non-linear manner, thus showing band bowing, typical for mixed systems. A new method has been developed to increase the hydrogen content in the bulk. This doping depends on the composition in an almost linear manner. The observed OH stretch mode spectra have been deconvoluted into three sub bands which can be attributed to different sites in the lattice. The composition dependent spectra have been modelled with a few parameters, using different line shapes and both linear and quadratic dependences of the band position.Raman spectra of several crystals of different composition were recorded for four different scattering configurations. Changes for wave numbers below 500 have been found, but could not attributed to particular modes. A prominent feature at about 600 wave numbers was not disturbed by other modes allowing a decomposition and an assigned of this mode to a certain vibration. It was found that the behaviour of this mode is governed by the [Sr]/[Ba] ratio in the pentagonal channel of SBN-x.The ferroelectric relaxor phase-transition of SBN-x has been studied with pyroelectric measurements. From the nonlinear susceptibility as a function of temperature the phase-transition temperature was deduced using the inflection point. The non fully-linear dependence of the phase-transition temperature as a function of the [Sr]/[Ba] ratio can be explained by a system of three different sublattices for the Strontium and Barium atoms.First results obtained with a setup for measuring the dielectric constant confirmed already reported data of other groups.
URL: https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2004121518
Subject Keywords: Strontium Barium Niobate; Sr; Ba; Nb; SBN; ferroelectric; band edge; phase-transition temperature; Raman scattering; pyroelectric; dielectric
Issue Date: 15-Dec-2004
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB04 - E-Dissertationen

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