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Condensed Matter Seminars

ics Condensed Matter
Thursday, April 3, 2008
4:00 PM
Physics Building, Room 204
Note special time.
Note special room.
Peter Gehring [Host: Seunghun Lee]
"Effects of Short-Range Order on the Structure and Dynamics of Relaxor Ferroelectrics"
 Slideshow (PDF)
Relaxors are disordered perovskite (ABO3) oxides, typically characterized by the presence of mixed valence B-site cations, that have found widespread use in numerous device applications because they exhibit low hysteresis and record-setting piezoelectric coefficients. Relaxors derive their name from an unusually frequency-dependent dielectric susceptibility, but they also display a rich variety of unusual physical phenomena including simultaneously soft zone-center and zone-boundary phonons, temperature dependent diffuse scattering, and an anomalous thermal expansion where a transition to a low-temperature invar-like behavior is observed. Recent neutron elastic and inelastic scattering results on the lead-based relaxors PbMg1/3Nb2/3O3 (PMN),PbZn1/3Nb2/3O3 (PZN), and their solid solutions with PbTiO3 will be discussed that indicate the development of static, short-range polar order at high temperatures is central to these phenomena. These results can be understood by analogy with random-field models in which just two temperature scales are required to describe the essential features of relaxor compounds.

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