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   COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS        
                   School of Computational Sciences	
                           (CSI 898-Sec 001) 
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              Physics and Design of Polydomain Materials

                     Alexander Roytburd
                 Materials Science Department, 
            University of Maryland, College Park, MD 

Polydomain micro- and nano-structures are natural products of phase
transformations in solids.  The trend to minimize the energy of internal
long-range fields (magnetic, electric or mechanical) leads to the formation
of arrangement of domains of different phases or differently oriented
domains of the same phase.  Transformations of bulk material usually result
in formation of complex irregular polydomain structures, which are
difficult to control.  However, the advance of thin film technology makes
it possible to obtain completely controlled polydomain structures with
desirable properties.  The point of this talk is to show how controlled
structures of elastic domain can be designed in constrained single
crystalline layers and how these structures can be optimized by engineering
of special types of constraint.

As examples, first, the ferroelectric films on substrates are considered
and it is shown that the engineering of polydomain structures allows one to
optimize the electrical and piezo  response of thin films.

Then, the multilayer composites consisting of alternation of transformable
(active) and non-transformable (passive) layers of micro- and nano-scale
thickness are considered.  The polydomain structure in active layers is
determined completely by parameters of the initial superlattice (layers'
thickness, their misfit and orientation).  Changing these parameters
governs the polydomain formation due to constrained martensitic
transformation.  Consequently, mechanical properties of  the polydomain
"supercrystal" can be modified demonstrating superelasticity (giant
reversible deformation)  or  high damping.

Finally,  perspectives and difficulties of design of polydomain
nano-composites are discussed.

                        Monday, April 9, 2001
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served at 4:15 PM.
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Find the schedule at http://csi.gmu.edu/lcdm/seminar/schedule.html