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Dislocation-Based Functionality in Oxides

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If you have a question about this talk, please contact Yonatan Calahorra.

While my group in the last 14 years worked mostly on lead-free piezoceramics, this topic has matured considerably and we now mostly work with industry to transfer knowledge into application. Our new topic with currently four researchers and four openings centers on dislocation-based functionality: Dislocations in oxides are typically heavily charged and embedded in a shell of compensating space charges. Therefore they provide a linear or two-dimensional array of charges stable up to high temperature without any chemical dopant. In the literature dislocations have been demonstrated to enhance oxygen conductivity and to improve the figure of merit of thermoelectrics by reducing thermal conductivity through phonon scattering by dislocations. Dislocations have been suggested to improve interfacial reaction kinetics and have been theoretically predicted to pin domain walls in ferroelectrics. In Darmstadt we have so far focused on establishing a set of techniques to introduce a high density of bulk dislocations into single crystals at room temperature or enhanced temperature and to study (dislocation) creep in polycrystalline oxides. Structural investigations have been performed by dark-field X-ray diffraction, rocking curve analysis, TEM , PFM, NMR and etching techniques. The first property evaluations have been done with respect to electrical and thermal conductivity and domain wall pinning. Select examples will be provided on dislocation structures, electrical and thermal conductivity. We have been working on SrTiO3, BaTiO3, KNbO3, TiO2 and ZrO2.

This talk is part of the Department of Materials Science & Metallurgy Seminar Series series.

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