In the present thesis the relaxor properties of the tungsten-bronze ferroelectric material strontium-barium niobate Sr<sub>1-w</sub>Ba<sub>w</sub>Nb<sub>2</sub>O<sub>6 </sub>(SBN) are investigated. SBN is a very good experimental realization of the three-dimensional random-field Ising model (3d <i>RFIM</i>). The quenched random fields (<i>RF</i>) originate from charge disorder and can be enhanced by doping with Ce<sup>3+</sup>. They are responsible for the formation of polar nanoclusters in the paraelectric phase. In order to study the critical behavior of SBN, linear birefringence (<i>LB</i>) and second harmonic generation (<i>SHG</i>) have been measured as a function of temperature. Within an Ornstein-Zernike analysis of the <i>LB</i> data the autocorrelation function, <<i>P</i><sup>2</sup>>, was determined, whereas the dipolar correlation length was obtained from the <i>SHG</i> data. They suggest that, due to its intrinsic disorder, pure SBN does not belong to the 3d Ising universality class. Doping with Ce<sup>3+</sup>ions, which seem to generate <i>RF</i>s, enhances the relaxor properties. The critical exponents <i>v</i> and <i>y</i> of SBN:Ce shift against those of the 3d <i>RFIM</i>. The domain morphology of SBN:Ce has been investigated by piezoelectric force microscopy (<i>PFM</i>). Fractal-like shaped zero-field cooled nanodomains are observed. Their size distribution can be described by a power law with exponential cutoff in accordance with prediction for the <i>RFIM</i>. It was measured for the first time in a <i>RF</i> system. The temperature and field induced evolution of natural and written domains has been studied with <i>PFM</i>, <i>LB</i> and <i>SHG</i> measurements. It reveals a very slow relaxation from a macrodomain into a depolarized multidomain state (and vice versa) even above <i>T<sub>C</sub></i>. This hints at strong pinning forces due to quenched <i>RF</i>s. They are also responsible for the observed aging in poled SBN and the field induced cluster percolation above <i>T<sub>C</sub></i> measured with <i>SH</i>-hysteresis. The domains can be considered as a "thick" phase grating for <i>SH</i>-diffraction. The Bragg-regime diffraction efficiency reflects the temperature and field induced change of the averaged domain sizes in the system.
| Identifer | oai:union.ndltd.org:DUETT/oai:DUETT:duett-12132001-102821 |
| Date | 13 December 2001 |
| Creators | Lehnen, Peer |
| Contributors | PD Dr. Axel Carl, Prof. Dr. Wolfgang Kleemann |
| Publisher | Gerhard-Mercator-Universitaet Duisburg |
| Source Sets | Dissertations and other Documents of the Gerhard-Mercator-University Duisburg |
| Language | German |
| Detected Language | English |
| Type | text |
| Format | text/html, application/pdf |
| Source | http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-12132001-102821/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. Hiermit erteile ich der Universitaet Duisburg das nicht-ausschliessliche Recht unter den unten angegebenen Bedingungen, meine Dissertation, Staatsexamens- oder Diplomarbeit, meinen Forschungs- oder Projektbericht zu veroeffentlichen und zu archivieren. Ich behalte das Urheberrecht und das Recht das Dokument zu veroeffentlichen und in anderen Arbeiten weiterzuverwenden. |
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