Event Scheduled for Aug 2, 2017
Event: PhD Dissertation Defense: M. Tumerkan Kesim
Time: 01:00 pm
Details of Event:
PhD Dissertation Defense
Presenter: M. Tumerkan Kesim
Major Advisor: Dr. S Pamir Alpay
Associate Advisors: Dr. Avinash M. Dongare, Dr. Serge M. Nakhmanson, Dr. Mark Aindow, Dr. Seok-Woo Lee.
Date: Wednesday, August 2, 2017
Time: 1:00 pm
Title: Dielectric and Electrothermal Properties of Ferroelectric Multilayers and Superlattice Heterostructures
Artificial ferroelectric (FE) heterostructures show unique electrical properties compared to bulk and single-crystal FEs. The internal built-in electrical fields due to heterogenoeuos nature of the structure gives rise to electrical properties that are not observed in a bulk FE. Dielectric and electrothermal (pyroelectric and electrocaloric) properties of such multilayers and superlattice heterostructure are investigated using a non-linear thermodynamic model. The underlying reasons for the enhancement of electrical properties of FE heterostructures are analyzed based on the strain and built-in electrostatic fields that could be used as design parameters under realistic processing conditions of such materials. It is shown that the choice of multilayer/substrate pair, processing/growth temperature, and relative layer fraction of ferroelectric could be tailored to enhance dielectric and electrothermal properties of FE multilayers. For instance, large tunabilities (90% at 400 kV/cm) are possible in carefully designed barium strontium titanate-STO and PZT-STO even on Si for which there exist substantially large in-plane strains. It is also possible to obtain enhanced electrocaloric response from multilayers. 0.75·BTO-0.25·PZT and 0.35·STO-0.65·PZT bilayers show ~120% and 65% increase in electrocaloric response, respectively, compared to PZT films on Si for ΔE=500 kV/cm. It is possible to obtain enhanced dielectric and pyroelectric response from PZT-STO superlattices (SLs), especially with increased number of repeating unit for a fixed thickness. It is possible to avoid domain splitting in the FE and obtain enhanced properties with reduced overall transition temperature. For example, small bias pyroelectric coefficient of 8-unit symmetrical SLs is ~55% higher than that of a zero bias PZT monolayer reaching 0.045 µC cm-2K-1.
Sponsored By: Materials Science and Engineering Program
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