T_cSUH Bi-Weekly Seminars

Friday, August 21, 2009

Room 102, University of Houston Science Center

12:00 PM - 01:00 PM

There are significant challenges to characterizing YBa2Cu3O7-δ (Y123) by electron microbeam but the results obtained have considerable utility. Few samples of Y123 have that cation stoichiometry. Variations within individual monoliths are used to map crystallization sequence and it will be shown that this is not necessarily from a single nucleus. Melting relations under different partial pressures of oxygen are employed to show that copper is in mixed valence state in Y-Ba-Cu oxide liquids even in pure oxygen and this has its own influence on the phase relations and in crystallization of Y123. Determination of oxygen content of Y123 is critical in its characterization but is altered by procedures used to prepare samples for analysis and by aging of the samples. The Cu L self-absorption spectrum of Y123 shows marked changes with oxygen doping and varies within some samples on a micron-scale.

Dr. Jim Meen has been a Research Associate Professor since 1995 and the Task Leader of the Materials Characterization Facility since 2002 at TcSAM. Previously he was a Research Assistant Professor, TcSUH (1990-1995); a Visiting Assistant Professor, University of North Carolina, Chapel Hill (1986-1990); and a Post-doctoral Fellow, Pennsylvania State University (1985-1986); He received his B. A. in Mineralogy and Petrology, Cambridge University, U.K. (1978); his M.Sc. in Geochemistry, Oxford University, U.K. (1979); and his Ph.D. in Geochemistry and Mineralogy, Pennsylvania State University (1985).