cfaed Seminar Series
cfaed Seminar Series
Prof. Dr. Dragan Damjanovic , Group for Ferroelectrics and Functional Oxides, EPFL
Domain Walls and Defects in Ferroelectrics: The Case of Conducting Domain Walls in BiFeO3
, 13:00 - 14:00
Werner-Hartmann-Bau, WHB205 , Nöthnitzer Str. 66 , 01187 Dresden
Properties of ferroelectric materials are in a large degree controlled by defects. This is the case for both polarization switching and for motion of domain walls under subswitching conditions. The latter controls weak-to-moderate field piezoelectric and dielectric properties. In addition, defects affect conductivity of the material, which can interfere with the coupling of electrical and mechanical properties.
Most of the studies on defects have been carried out on classical ferroelectrics, BaTiO3 and Pb(Zr,Ti)O3. Concepts of ageing, "hard" and "soft" ferroelectrics have thus been developed and soft and hard ferroelectrics have become important technological materials. However, physics and chemistry of ferroelectrics in general are much more complex. A good example is BiFeO3, the most widely studied multiferroic. As in other ferroelectrics, domain walls in BiFeO3 can be charged or electrically conducting but, in addition and in contrast to PZT or BaTiO3, B-site ion (Fe), can have a higher (Fe+4) or lower (Fe+2) valence than the host cation (Fe+3). We will show that this multiple valence state of Fe results in interesting behavior, including high conduction of domain walls. Since domain walls' displacement can be responsible for a large part of the macroscopic electro-mechanical effect of a ferroelectric, their conducting nature in BiFeO3 leads to interesting and unusual dependence of the piezoelectric properties on amplitude and frequency of the driving electric field.
Dragan Damjanovic received BSc diploma in Physics from the University of Sarajevo in 1980, and PhD in Ceramics Science from the Pennsylvania State University (PSU) in 1987. From 1988 to 1991 he was a research associate in the Materials Research Laboratory at the PSU working on pyroelectric properties of synthetic polypeptides, piezoelectric composites for underwater applications and thermo-optical imagers. He joined the Ceramics Laboratory, Institute of Materials, at the Swiss Federal Institute of Technology in Lausanne (EPFL) in 1991. He is currently a professeur titulaire and teaches undergraduate and graduate courses on electrical properties of materials. He investigates experimentally physical processes taking place at different driving field and time scales and how they affect macroscopic behavior of ceramics, polymers, single crystals and thin layers. His interests include lead-free materials for electro-mechanical energy conversion, interaction of defects with domain walls, symmetry breaking and its effect on electro-mechanical and electro-thermal coupling, interface dynamics, dispersion, creep, nonlinearity and hysteresis in dielectric, mechanical and piezoelectric responses, phase transition-related instabilities, structure/ microstructure–property relations, and applications of dielectric, piezoelectric and ferroelectric crystals, films, and ceramics. He is an IEEE Fellow, was awarded 2007 Outstanding Achievement Award by the International Symposium on Integrated Ferroelectrics and 2009 Ferroelectrics Recognition Award by the IEEE Ultrasonics, Ferroelectrics and Frequency Control (UFFC) Society, was Distinguished Lecturer for the IEEE UFFC Society for 2010/11. Since 2015 he is the Vice President for Ferroelectrics of the IEEE UFFC Society. He authored and co-authored more than 200 papers (citation metrics can be seen at http://www.researcherid.com/rid/A-8231-2008).