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ion Processing Lead-Free Piezoelectrics at Lower

Energy ConsumptionXiaoli Tan, Iowa State University, DMR 1037898

Outcome: Researchers at Iowa State University have gained new insights in the physical mechanisms that govern the change in dimensions in a group of lead-free oxides under applied electric fields. Impact: The discovery could help to eliminate lead, the substance detrimental to the environment and human health, from ceramics that are widely used in our everyday life, such as speaker phones and ultrasonic medical imaging devices.

Explanation: Piezoelectric ceramics change their dimensions when exposed to an electric field. They are critical to numerous engineering technologies. However, currently used materials contain high amounts of lead.

Professors Xiaoli Tan and Scott Beckman, of Iowa State's Department of Materials Science and Engineering, worked jointly and discovered a new processing technique for lead-free piezoelectric ceramics. The discovery suggests that the environmentally friendly ceramic can be produced with reduced energy consumption.

The co-PI Beckman and Ms. Jordan Barr, the undergraduate research assistant, discuss their recent computed results. (Courtesy of Beckman )

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ion Electrical Poling below Coercive Field for Large Piezoelectricity

Xiaoli Tan, Iowa State University, DMR 1037898

• Isotropic polycrystalline ferroelectric ceramics have to be electrically poled to develop a net macroscopic polarization and hence piezoelectricity. It is well accepted that a sufficient poling can only be realized under an electric field that is much higher than the coercive field.

EC: Coercive field

EF: Phase transition field

EP: Required poling field

• The researchers at Iowa State discovered that in (Bi1/2Na1/2)TiO3BaTiO3 ceramics, large piezoelectricity can develop at poling fields far below the measured coercive field (below). Using in-situ transmission electron microscopy, such an unusual behavior is interpreted with the polarization alignment of polar nanodomains in the non-ergodic relaxor phase (right).

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ion Graduate, Undergraduate and High School Students Training

Xiaoli Tan, Iowa State University, DMR 1037898• Two graduate students supported by this project obtained their PhD degrees and are now

employed by the Oak Ridge National Laboratory and the Lawrence Berkeley National Laboratory. • Last year, the graduate students on this project won the following awards at Iowa State:

Research Excellence Award, Best Paper Award, Go-For-The-Gold, and the Zaffarano Prize. • Ms. Jordan Barr, the undergraduate student working on this project, presented a paper

“Electrocaloric Effect in Lead-free Ceramics: BaTiO3 and KNbO3” at the 2013 Materials Research Society Spring Meeting on April 3, 2013 at San Francisco. She also published her results in in Materials Letters 89, 254-7 (2012).

• A group of Ames High School Science Olympiad team members were hosted by the PI on April 20, 2013 in the Department of Materials Science and Engineering teaching lab to prepare them for the National Tournament on the Materials Science event. The high school students were exposed to basic crystallography, materials classifications and their properties. They also watched live experiments on indentation, uniaxial tension, and Charpy impact tests.

• Research findings were widely disseminated, including the following high-impact publications:– C. Ma, H.Z. Guo, S.P. Beckman, and X. Tan, “Creation and destruction of morphotropic phase

boundaries through electrical poling: A case study of lead-free (Bi1/2Na1/2)TiO3–BaTiO3 piezoelectrics,” Physical Review Letters 109, 107602/1-5 (2012).

– H.Z. Guo, C. Ma, X.M. Liu, and X. Tan, “Electrical poling below coercive field for large piezoelectricity,” Applied Physics Letters 102, 092902/1-4 (2013).

– C. Ma, H.Z. Guo, and X. Tan, “A new phase boundary in (Bi1/2Na1/2)TiO3–BaTiO3 revealed via a novel method of electron diffraction analysis,” Advanced Functional Materials, in press, 2013. DOI: 10.1002/adfm.201300640.