Research Briefs

aug13

Aerodynamic levitation, modeling, new analytical techniques lead to cement-to-semiconductor advances Normally, creation of a metallic glass begins with a metal that is transformed to a glassy state. Recently an international research team demonstrated a novel way to make metallic glass. The process starts with a type of cement that is heated with a laser while floating in a container, which leads to creation of a material that surprisingly behaves like a semiconductor at room temperature. After characterizing it with X-ray and neutron diffraction and extended X-ray absorption, this material was successfully matched with models that help explain this nonintuitive behavior and point the way to the discovery of other unexpected semiconductors. The researchers focused on several glass compositions, including 64 mol% CaO (64CaO) glass and 50CaO glass, combining multiple computational and experimental techniques to determine what is going on in the new material. To obtain samples, the group used a tool called an “aerodynamic levitator” in which they heated the cement with a laser to 2,000°C. The levitator prevented the melting cement from touching the sides of the heating vessel, suppressed crystal growth, and allowed the material to cool as a glass. They then compared predictions based on the structural models with analytical results and found close correlation. According to the researchers, as the material cooled, free electrons were trapped via “efficient elemental mixing” in cagelike structures. These trapped electrons are at the root of the unusual conductive behavior in the glass. “This phenomenon of trapping electrons and turning liquid cement into liquid metal was found recently, but not explained in detail until now,” says Chris Benmore, a physicist from the US Department of Energy’s Argonne National Laboratory (Argonne, Ill.), in the lab’s news release. “Now that we know the conditions needed to create trapped electrons in materials, we can develop and test other materials to find out if we can make them conduct electricity in this way.” The appeal of this type of metallic glass could be very strong because its properties (not brittle, corrosion resistant, easily processed and molded) would provide new nonmetal options for engineers and designers. One application Benmore predicts is thin-film resistors used in liquid-crystal displays. Materials Development Inc.’s (Arlington Heights, Ill.) Rick Weber, also a member of the research group, is excited by the work that has been done so far. He said the effort united novel processing, advanced analytical techniques, rigorous modeling, and supercomputing to deliver “good, fundamental science. It was great that our modeling matched our experimental data, but this was a very nonintuitive result. It is a real-life example of how researchers have to be open to new ideas and how we can use this array of tools to open up new areas of research.” Results of the work are reported in Proceedings of the National Academy of Sciences in the article “Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses.” n Sintering of Ceramics Short Course on DVD NEW! Special Introductory Learn sintering fundamentals at your own pace, or host multi-person training sessions at your facility. Taught by Dr. Mohamed N. Rahaman, the course covers sintering basics; di usion and defect chemistry; solid-state, viscous and liquid-phase sintering; microstructure development and control; and much more. Take advantage of the $100 savings thru October 1st List: $665 $565 ACerS Member: $595 $495 14 www.ceramics.org | American Ceramic Society Bulletin, Vol. 92, No. 6 (Credit: Akola et al.; Argonne National Lab.) research briefs One type of cage structure around the spin-density of one electron in a model of cement-based semiconducting metallic glass (gray=Al, green=Ca, and red=O). www.ceramics.org/sinteringdvd Rate


aug13
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