Seminar Announcement

Professor Frank (Bud) Bridges

University of California Santa Cruz

"Unusual Local Distortions in Crystals:
the Underlying Cause for Many Observed Macroscopic Properties"

Date: Thursday, January 20, 2005
Time: 4:10 pm.

Abstract:

In many systems, macroscopic properties such as metal/insulator transitions, unusually low thermal conductivity in crystals, and magnetism are determined by small distortions at the unit cell level. Such local distortions can be generated by thermal vibrations, polarons, static strain, or small structural transitions, but often are determined by novel features of the lattice structure, particularly in system with more complex unit cells. I will first review some aspects of the local structure that can be probed with the Extended X-ray Absorption Fine Structure (EXAFS) technique. Then using this tool I'll discuss local structure studies of low thermal conductivity systems such as the filled skutterudites and Ga/Ge clathrates (both are thermoelectric materials) and also metal/insulator transitions in a skutterudite and in colossal magnetoresistive manganites. For the latter, changes in the local distortions are directly related to the sample magnetization.