Publications
Interfacial structure in Telluride-based thermoelectric materials
Chalcogenide compounds based on the rocksalt and tetradymite structures possess good thermoelectric properties and are widely used in a variety of thermoelectric devices. Examples include PbTe and AgSbTe2, which have the rocksalt structure, and Bi2Te3, Bi2Se3, and Sb2Te3, which fall within the broad tetradymite-class of structures. These materials are also of interest for thermoelectric nanocomposites, where the aim is to improve thermoelectric energy conversion efficiency by harnessing interfacial scattering processes (e.g., reducing the thermal conductivity by phonon scattering or enhancing the Seebeck coefficient by energy filtering). Understanding the phase stability and microstructural evolution within such materials is key to designing processing approaches for optimal thermoelectric performance and to predicting the long-term nanostructural stability of the materials. In this presentation, we discuss our work investigating relationships between interfacial structure and formation mechanisms in several telluride-based thermoelectric materials. We begin with a discussion of interfacial coherency and its special aspects at interfaces in telluride compounds based on the rocksalt and tetradymite structures. We compare perfectly coherent interfaces, such as the Bi2Te3 (0001) twin, with semi-coherent, misfitting interfaces. We next discuss the formal crystallographic analysis of interfacial defects in these systems and then apply this methodology to high resolution transmission electron microscopy (HRTEM) observations of interfaces in the AgSbTe2/Sb2Te3 and PbTe/Sb2Te3 systems, focusing on interfaces vicinal to {l_brace}111{r_brace}/{l_brace}0001{r_brace}. Through this analysis, we identify a defect that can accomplish the rocksalt-to-tetradymite phase transformation through diffusive-glide motion along the interface.