Dislocation-based Functionality in Oxides
11:00 - 12:00
Prof. Jürgen Rödel
Nonmetallic-Inorganic Materials, Department of Materials- and Geosciences, TU Darmstadt
Max-Planck-Institut für Eisenforschung GmbH
Large Conference Room No. 203
on invitation of Dr. Christian Liebscher and Prof. Gerhard Dehm
Dislocations in oxides are typically heavily charged and are surrounded by compensating electric charges. As such they are kinetically more stable than chemical dopants. Adepalli et al. termed dislocations a means for “one-dimensional doping” . As they are often introduced by mechanical methods, they may also be termed “mechanical doping” or “self-doping”, as the charges derive from local concentration of the matrix elements. In the literature dislocations have been demonstrated to enhance oxygen conductivity  and 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 dislocations into single crystals at room temperature or enhanced temperature and to study (dislocation) creep. Structural investigations have been performed by dark-field X-ray diffraction, rocking curve analysis , TEM, NMR and EPR techniques. The first property evaluations have been done with respect to electrical and thermal conductivity and domain wall pinning. All this has to be seen with the perspective of a just developing field, with many opportunities, many obstacles and a lot of exciting uncertainty. Select examples will be provided on dislocation structures, electrical and thermal conductivity in SrTiO3 and our first attempts on dislocation creep in BaTiO3. Time provided, I will show 4 slides on the small brother field: “Elastic-deformation tuned conductivity in piezoelectric ZnO."  Adepalli, K. K., Kelsch, M., Merkle, R., and Maier, J., "Enhanced ionic conductivity in polycrystalline TiO2 by "one-dimensional doping''," Phys. Chem.Chem. Phys., 16 4942-51 (2014).  S. Il Kim, K. H. Lee, H. A. Mun, S. H. Kim, S. W. Hwang, J. W. Roh, D. J. Yang, W. H. Shin, X. S. Li, Y. H. Lee, G. J. Snyder, S. W. Kim, “Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics“, Science, 348, 109-114 (2015).  E.A. Patterson, M. Major, W. Donner, K. Durst, K.G. Webber and J. Rödel, „Temperature dependent deformation and dislocation density in SrTiO3 single crystals”, J. Amer. Ceram. Soc., 99, 3411-120 (2016).