Event
MSE Seminar - Prof. Alexander Roytburd, University of Maryland
Friday, May 2, 2008
1:00 p.m.
Rm. 2108, Chemical and Nuclear Engineering
Annette Mateus
301 405 5207
amateus@umd.edu
"Elastic Domains: Self-Assembled Micro- and Nanostructures from Steel to Thin Film Multiferroics"
The discovery of polydomain phases has been one of the fundamental results of the experimental and theoretical studies of solid phase transformations. Polydomain phases consist of the alternative domains: twins of a product phase or layers of different product phases. These elastic domains minimize the energy of elastic interactions similar to electric and magnetic domains which minimize energy of long range electrostatic and magnetic interactions in ferroelectrics and ferromagnetics. Thermodynamic concept of elastic domains allows us to understand and predict fundamental features of formation of micro- and nanostructure at phase transformations in solids.
Studies of effects of artificial constrains on polydomain structure have led to the theory of adaptive composites consisting of layers of transformable phases constrained by passive layers. It will be shown that unusual thermodynamic properties of adaptive composites including negative elastic modulus at strain controlled deformation and thermodynamic hysteresis at stress controlled deformation can be controlled by the change of relative thickness and elastic properties of component layers.
Expansion of the theory of elastic domains to epitaxial films has led to intensive experimental and theoretical studies of polydomain structures in shape memory metals, superconductor and ferroelectrics oxide films. The self-assembled structure of non-180o elastic domain with optimum mechanical, electrical, pyroelectrical and piezoelectrical properties had been theoretically designed and experimentally engineered.
The development of the concept of heterophase polydomain structures consisting of domains of different phases serves as theoretical background for engineering of self-assembled nanostructures in epitaxial thin films . Self-assembled multiferroic nanostructures consisting of ferroelectric and ferromagnetic phases have been modeled and experimentally synthesized. It has been shown that the morphologies can be controlled by changing of constrain conditions through the change of substrate orientation. In these structures, the elastic interaction between domains generates the coupling magnetic and electric properties.
Exploring equilibrium domain structures in non-uniform external field and graded crystals have resulted in discovery of domains with wedge morphology. It is suggested that the wedge domain structures should have enhanced sensitivity to external mechanical and electrical field as well to change of temperature.
The idea of wedge domains has been successfully applied to bent nanocrystalline films undergoing the structure transformation to a lower symmetry phase. The elastic interaction between transformed grains results in the self-organization and formation of polycrystalline macrodomains. The wedge macrodomains has been observed in bent films after cubic to tetragonal transformation in BaTiO3. These films demonstrate giant pyroelectrical effect due to high mobility of macrodomain structures.
For more information, contact Annette Mateus at (301) 405-5207 or amateus@umd.edu.
