National Science Foundation Toward a Greener World: The Development of Lead-Free Electroceramics Xiaoli Tan, Iowa State University, DMR Outcome: Researchers at Iowa State University have gained new insights in the physical mechanisms that govern the change in dimensions and temperature 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 while electrocaloric materials change their temperature when exposed to an electric field. Both types of electroceramics 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 new functioning mechanisms in lead-free electroceramics. The co-PI Beckman and Ms. Jordan Barr, the undergraduate research assistant, discuss their recent computed results. (Courtesy of Beckman )

National Science Foundation Solid-State Refrigeration Through Electrocaloric Effect Xiaoli Tan, Iowa State University, DMR The electrocaloric effect (ECE) causes a material to spontaneously change temperature when exposed to an applied electric field. Scientists at Iowa State University have found that for a group of lead-free compounds it is possible to achieve a large electrocaloric temperature change for a modest applied field. This is counter to the current trend in research where scientists and engineers are examining lead-containing materials that require fields approaching the breakdown strength. The theoretical approach employs a model that is parameterized purely from first-principles, quantum mechanical calculations. The ECE is particularly promising for application as a solid-state refrigeration technology. Domestic refrigeration for food storage is a major consumer of energy. The US Energy Information Administration reported that in % of household electricity is used in the kitchen and that of this 64% goes toward cooling food. Refrigerators are relatively low efficiency devices that require a large mechanical condenser to compress a gas. Moving to solid-state cooling has the potential to dramatically increase the efficiency of refrigeration devices because it is based on changing the local structure (order) of atoms in a crystal by directly applying an electric field to the crystal. Because so much energy is used for refrigeration, even a modest increase in efficiency would result in a dramatic savings.

National Science Foundation Lead-Free Piezoelectrics New insight: With the unique electric field in situ transmission electron microscopy (TEM) technique, the researchers at Iowa State discovered that the morphotropic phase boundary can be created, destroyed, or even replaced with a new one during electrical poling. The microstructural evolution correlates extremely well with the macroscopic piezoelectric property. This discovery is in sharp contrast with lead-containing ceramics, such as Pb(Zr,Ti)O 3, where only ferroelectric domain switching takes place during electrical poling. The results indicate that high piezoelectric performances can be achieved even in single phase compositions, which have always been excluded previously in the search for lead-free compositions. In situ TEM bright field images along the [112] zone-axis of an originally phase-pure P4bm grain in the 0.94(Bi 1/2 Na 1/2 )TiO BaTiO 3 ceramic under different electric fields are displayed to demonstrate the creation and destruction of the R3c/P4mm MPB during poling. (a) 0 kV/mm. (b) 3.2 kV/mm. The boundary between the volume with R3c wedge-shaped domains (region R) and that with P4mm lamellar domains (region T) is highlighted by bright dotted lines. The dark arrow indicates the direction of applied fields. (c) 3.6 kV/mm. (d) 4.0 kV/mm. Xiaoli Tan, Iowa State University, DMR