Coupled Atomistic and Thermodynamic Calculations of Point Defect Energetics in TiO 2 DMR-0303279

1. Coupled Atomistic and Thermodynamic Calculations of Point Defect Energetics in TiO2DMR-0303279 Elizabeth Dickey, Penn State Univ. and Susan Sinnott, Univ. of Florida (Figure Below) Atomic model of a Ti ion in an interstitial site, denoted Tii , in the TiO2 crystalline lattice. TiO2 is used in a wide variety of electrical, dielectric and sensing applications. Point defects in the crystalline lattice play an important role in its electronic and functional properties.We have developed a computational approach that integrates first-principles electronic-structure and thermodynamic calculations to determine point defect stabilities in TiO2 over a range of temperatures, doping levels and oxygen partial pressures. This data allows us to predict material nonstoichiometry and electrical conductivity as a function of the material environment. 5nm Tii. VOx Tii... (Figure Right) Stability diagrams for predominant point defects in TiO2 as a function of temperature, oxygen partial pressure and Fermi level (F). Tii represents a titanium interstitial, Vo a vacancy on an oxygen site and VTi a vacancy on a titanium lattice site. The superscript denotes the charge ( ‘ positive and . negative) Temperature (K) VO.. VTi VTi εF=2.5eV εF=1.5eV Oxygen Partial Pressure, log(P/P0)

2. Research Experiences for High School and Undergraduate Students in Oxide Electroceramics DMR-0303279Elizabeth Dickey, Penn State Univ. and Susan Sinnott, Univ. of Florida Mentoring and training both undergraduate and high school students is an integral part of the research program. John Foreman, an undergraduate student at Penn State, has been gaining valuable research exposure and experience by selectively doping TiO2 to study the effects on grain boundary properties. This experience has motivated John to pursue a graduate degree in Materials Science after his graduation in Dec. 2006. Riley Butler, an undergraduate student at UF, has been working with UF graduate students Jun He and Patrick Chiu to carry out combined electronic structure and thermodynamics calculations to determine defect formation energies in metal oxides. Leah Nation also worked with Patrick Chiu to carry out molecular dynamics simulations of oxide surface chemistry. She was a UF Student Science Training Program participant during the summer of 2006. Leah Nation and Patrick Chiu at the University of Florida, July, 2006