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Building new ferroelectrics layer by layer  
Ferroelectric materials possess extremely useful functional properties, such as a switchable electronic polarization, and high dielectric constants and piezoresponse. Matt Dawber's group , supported by the Ceramics program of the National Science Foundation through a CAREER award, is leading a research program to develop new and improved ferroelectric materials by depositing different perovskite oxide materials in extremely fine layers, one on top of another.

In a recent paper (Phys. Rev. Lett. 109, 067601 (2012)) they describe results on combining a ferroelectric material, lead titanate, and a material that is normally metallic, strontium ruthenate. As the strontium ruthenate layers are very thin, the conductivity in the new artificial material is very low in the direction of the ferroelectric polarization. The new material thus behaves like a ferroelectric, but one that has a strong preference for one polarization direction over another. This effect is driven by a breaking of symmetry across the interfaces of the material. In addition to the polarization effect, the symmetry breaking also has the potential to allow coupling between ferroelectricity and magnetism. Compounds with this property are called "multiferroic" materials. An essential part of this work was a strong collaboration with the theory group of Marivi Fernandez-Serra , also in the Dept of Physics and Astronomy at Stony Brook.

Even more recently another publication from the group (Phys. Rev. Lett. 109, 167601 (2012)) showcased a different material system with quite different properties. Although the ferroelectric component in this system was again lead titanate, the other material was calcium titanate, chosen because it was hoped that it would induce polarization rotation and an associated enhancement of the piezoresponse and dielectric constant. By a detailed experimental study, this was shown to be the case, and a new pathway to piezoelectric materials has been opened by this work.

Both projects made extensive use of user facilities at nearby Brookhaven National Laboratory, particularly the National Synchrotron Light Source, which was used to identify structural changes in the materials by x-ray diffraction, and the Center for Functional Nanomaterials, where Dong Su performed electron microscopy which was critical to the success of both projects.


Click on the image to see a a schematic representation of a ferroelectric crystal.
2012-10-20

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