In this project, the displacement of defect ions and atoms in insulating crystals will be studied. Paraelectric resonance experiments, using hydrostatic pressure, will investigate the on- to off-center transitions in several systems. EXAFS (extended x-ray absorption Fine Structure) will measure directly, independent of the charge state, the off-center displacement of ions or atoms such as Ag;s+, Cu;s+, Co;s2;s+, Ag;so and Cu;so. In some cases, it will measure for the first time, the distortion of the lattice about an off-center defect. Data will also be obtained for the cation - anion distances in several series of defect systems in which the position of the defect varies from off-center to on-center. Some of these data will test Vegard's Law in systems for which there is a large difference in ionic radii. These experiments will provide needed information about the conditions required for off-center behavior.
