National Science Foundation Atomic Defects Hop to the Tune of Music Outcome: Professor Miladin Radovic from Texas A&M University and recipient of an NSF Faculty Early Career Development (CAREER) award, led the team that showed that large amplitude vibrations at the resonant frequencies can be significantly attenuated or damped in some, essentially rigid and brittle, doped metal-oxide ceramics even at elevated temperatures due to reorientation of clusters of the atomic defects (dopant- oxygen vacancy) that are common in those ceramics. Miladin Radovic,T exas Engineering Experiment Station, DMR Impact: This can be used to tailor mechanical response of oxide ceramics that are widely used in sensors and energy conversion devices, such as fuel cells by their selective doping with other oxides. These materials may also help dissipate sonic and ultrasonic vibrations in the large temperature range. Explanation: In most technologically important metal oxides, some of the host metal ions are substituted, i.e. doped, by other metal ions to tailor their physical properties, resulting in some vacant oxygen sites adjacent to the doping metal ions. When these doped oxides are exposed to the small periodic vibrations oxygen ions jump in and out of those vacant sites. Their hopping with the mechanical vibrations dissipates a large portion of mechanical energy. Prof. Radovic and Ph.D. student Peipei Gao next to the high temperature resonant ultrasound spectrometer developed at Texas A&M University. (courtesy Texas A&M University)

National Science Foundation Attenuation (damping coefficient) Q -1 vs. temperature determined by RUS for 20GDC. Maximum attenuation is used to determine the activation energy by the Arrhenius equation. Activation Energy of Defect Motion Miladin Radovic, Texas Engineering Experiment Station, DMR All objects oscillate at a greater amplitude at specific frequencies known as resonant frequencies, at which even small periodic driving force can produce large violent swaying motions and even catastrophic failure. One familiar example is the wine glass which can shatter when exposed to the sound. Researchers from Texas A&M University showed that large amplitude vibrations at the resonant frequencies can be significantly attenuated or damped in some metal-oxide ceramics even at elevated temperatures due to reorientation of the clusters of atomic defects (dopant-oxygen vacancy) that are common in those ceramics. The characteristic temperature and resonant frequency with the maximum attenuation was found to depend on the size of the substitute metal ion relative to the size of the host metal ion and amount of substituted metal ions. The temperature and frequency of maximum attenuation can be used to determine the activation energy for oxygen ion motion. This phenomena allows tailoring of the mechanical response of oxide by their selective doping with other oxides.

National Science Foundation Dr. Radovic frequently mentors undergraduate students during summer research projects. These students learn to use different equipment to aid in experimental work and data analysis. The students must also present their work at the end of the summer as a poster. This year, Gordon Morrow a freshman from Sam Houston State University worked on processing ceramic materials from powders to dense samples. REU Students Miladin Radovic, Texas Engineering Experiment Station, DMR REU student Gordon Morrow with is final poster presentation