First-Principles Based Prediction of High-Temperature Defect Chemistry and Conductivity of TiO 2 Elizabeth C. Dickey, Pennsylvania State Univ University Park, DMR TiO 2 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 energies in TiO 2 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. (Figure Right) Predicted electrical conductivity (solid lines) in comparison to measured properties from the literature (points) as a function of temperature and oxygen partial pressure with no adjustable parameters. (Figure Below) Atomic models of an oxygen vacancy (left) and Ti interstitial site, (right) in the in the TiO 2 crystalline lattice.

Education and Outreach S.B. Sinnott (Co-PI), University of Florida, DMR This research project has trained two University of Florida graduate students in ceramic engineering and computational materials science and engineering. One of these students, Dr. Jun He, starts a postdoctoral position at Argonne National Laboratory in September, The project has also trained two undergraduate students and five Student Science Training Program (SSTP) high school students. The SSTP students spend two months carrying out research with graduate student mentors. As part of the program, they also present their findings in an oral presentation at the end of the summer. Ms. Ann Dietrich, a 2007 University of Florida SSTP student, presents her research results on TiO 2 defect formation energies in group meeting.

Training of High School Students in Computational Materials Science and Engineering S.B. Sinnott (Co-PI), University of Florida, DMR Rutile TiO 2 Pyrolusite MnO 2 Cassiterite SnO 2 Cation radius (Å) Cation electron configuration [Ar]4S 2 3d 2 [Ar]4S 2 3d 5 [Kr]5S 2 4d 10 5p 2 Bond energy (kJ/mol, gaseous diatomic species) O vacancy formation energy (eV) Prof. Sinnott and graduate student, Mr. Jun He (left), mentored and worked with high school student, Mr. Leemen Weaver (right) on the described research. Mr. Weaver was a University of Florida Student Science Training Program participant during the summer of Mr. Weaver’s project was to understand oxygen vacancy formation in three rutile, metal oxides using first principles, density functional theory calculations. A sample unit cell is shown in the top, right-most figure. His preliminary results are shown in the table. They indicate that the cation electron configuration and bond energies are dominant factors in the formation of oxygen vacancies. Oxygen vacancy Cation (Ti, Mn, Sn)