Friday, October 25, 2013 from 04:00 PM to 05:00 PM

The speaker is our familiar professor, Dr. Alexei Grigoriev. He will talk about his recent research on ferroelectric bilayers.


Polarization Coupling in

Ferroelectric Bilayers

Dr. Alexei Grigoriev

Department of Physics & Engineering Physics

The University of Tulsa

Friday, October 25, 2013

4:00pm - 5:00pm

Keplinger Hall M216

Ferroelectric materials have a spontaneous electric polarization that does not vanish without anapplied electric field. This spontaneous polarization is coupled to elastic strain in ferroelectriccrystals enabling many interesting properties including piezoelectricity, pyroelectricity, and a huge tunable dielectric permittivity up to ε ~100 – 10,000 (for comparison, for glass ε ~ 4 – 10).

Properties of ferroelectric materials can be controlled by the growth parameters such as theepitaxial misfit strain during thin film growth. Strain and electrostatic interaction parametersbetween ferroelectric layers expand space for engineering ferroelectric multilayer materials withenhanced and possibly completely new properties. The focus of this talk will be on the most “trivial” case of ferroelectric bilayers. 

Landau-Ginzburg-Devonshire (LGD) thermodynamic theory of ferroelectrics predictspolarization, piezoelectric and dielectric responses of ferroelectric bilayers. Experimentalmeasurements of ferroelectric parameters of two different bilayer systems show that theinterlayer polarization coupling, which is used as a parameter of the LGD theory, is very weak.  This weak coupling allows for tail-to-tail and head-to-head polarizationdomains to exist. We observed theseunusual polarization domainformations in both structural andelectrical measurements. Thisobservation presents a new theoreticalchallenge of explaining the polarizationswitching charge compensation. Apossible explanation involves anenhancement of a charge carrierconcentration at the interface betweenferroelectric layers due to the electronenergy band bending and the formationof a highly localized conducting regionresembling the 2D electron gasformation in semiconductorheterojunctions. 

Sanwu Wang