Properties of ferroelectric ma
terials are in a large degree controlled by defects. This is the case for
both polarization switching and for motion of domain walls under subswitch
ing conditions. The latter controls weak-to-moderate field piezoelectric a
nd dielectric properties. In addition\, defects affect conductivity of the
material\, which can interfere with the coupling of electrical and mechan
ical properties.
Most of the studies on defects have been carried out o
n classical ferroelectrics\, BaTiO3 and Pb(Zr\,Ti)O3. Concepts of ageing\,
\"hard\" and \"soft\" ferroelectrics have thus been developed and soft an
d hard ferroelectrics have become important technological materials. Howev
er\, physics and chemistry of ferroelectrics in general are much more comp
lex. A good example is BiFeO3\, the most widely studied multiferroic. As i
n other ferroelectrics\, domain walls in BiFeO3 can be charged or electric
ally conducting but\, in addition and in contrast to PZT or BaTiO3\, B-sit
e ion (Fe)\, can have a higher (Fe+4) or lower (Fe+2) valence than the hos
t cation (Fe+3). We will show that this multiple valence state of Fe resul
ts in interesting behavior\, including high conduction of domain walls. Si
nce domain walls' displacement can be responsible for a large part of the
macroscopic electro-mechanical effect of a ferroelectric\, their conductin
g nature in BiFeO3 leads to interesting and unusual dependence of the piez
oelectric properties on amplitude and frequency of the driving electric fi
eld.
Bio:
Dragan Damjanovic received BSc diploma in Physics from the University of Sarajevo in 1980\, and PhD in Ce ramics Science from the Pennsylvania State University (PSU) in 1987. From 1988 to 1991 he was a research associate in the Materials Research Laborat ory at the PSU working on pyroelectric properties of synthetic polypeptide s\, piezoelectric composites for underwater applications and thermo-optica l 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 experiment ally physical processes taking place at different driving field and time s cales and how they affect macroscopic behavior of ceramics\, polymers\, si ngle crystals and thin layers. His interests include lead-free materials f or electro-mechanical energy conversion\, interaction of defects with doma in walls\, symmetry breaking and its effect on electro-mechanical and elec tro-thermal coupling\, interface dynamics\, dispersion\, creep\, nonlinear ity and hysteresis in dielectric\, mechanical and piezoelectric responses\ , phase transition-related instabilities\, structure/ microstructure–pro perty relations\, and applications of dielectric\, piezoelectric and ferro electric crystals\, films\, and ceramics. He is an IEEE Fellow\, was award ed 2007 Outstanding Achievement Award by the International Symposium on In tegrated Ferroelectrics and 2009 Ferroelectrics Recognition Award by the I EEE Ultrasonics\, Ferroelectrics and Frequency Control (UFFC) Society\, wa s 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 see n at http://www.researcherid.com/rid/A-8231-2008).
DTSTAMP:20260603T154551Z CREATED:20161221T074155Z LAST-MODIFIED:20170102T074546Z END:VEVENT END:VCALENDAR