Atomic Scale Investigations of Interfaces in Telluride-Based Thermoelectric Materials
Dr. Douglas L. Medlin
Materials Physics Department
Sandia National Laboratories
Interfaces strongly affect the thermal and electronic transport properties of thermoelectric materials. At present, however, the fundamental understanding of interfacial structure in thermoelectrics is in its infancy. Here, I will discuss our electron microscopic studies of the atomic structure of interfaces in telluride-based thermoelectric materials, considering both tetradymite structured materials, such as Bi2Te3, as well as heterophase interfaces between tetradymite and rock-salt structured tellurides, which have been investigated in the context of thermoelectric nanocomposites. A key theme throughout this work is to establish the underlying roles of interfacial line defects, such as dislocations and interfacial steps. I will begin with an analysis of low-angle grain boundaries in Bi2Te3, discussing the arrangement and core structure of the individual dislocations that accommodate small tilt misorientations in this material. Second, I will discuss the structure of high angle grain boundaries in Bi2Te3, considering in detail the (0001) basal twin and nature of defects at interfaces vicinal to this relatively simple and low energy interface. Finally, I will discuss the role of interfacial defects in controlling phase transformations and strain accommodation at tetradymite/rocksalt telluride interfaces.
Dr. Medlin received his Ph.D. in Materials Science and Engineering at the University of California, Davis, in 1992 and is presently a Distinguished Member of the Technical Staff at Sandia National Laboratories in Livermore, California. Electron microscopy serves as a central tool for his research, which is broadly concerned with how the atomistic and mesoscale structure of interfaces controls the microstructural evolution and functional properties of materials. His current research is on the structure of interfacial line defects, the mechanisms of solid-state phase transformations, and the behavior of interfaces in thermoelectric and other energy conversion materials.