Synthesis and Real Structure Group

SPP 1386

Nanostrukturierte Thermoelektrika: Theorie, Modellsysteme und kontrollierte Synthese


In the mid 1990s research in the field of thermoelectrics experienced a renaissance due to theoretical predictions that the thermoelectric efficiency could greatly be enhanced through nanostructural engineering. It seems that disorder and complexity in the unit cell of appropriate materials as well as nanostructuring are the most promising approaches for an enhanced efficiency.
The most important motivation for this joint project in the frame of SPP 1386 “Nanothermoelectrics” are the results reported by Venkatasubramanian [Appl. Phys. Lett. 75, 1999, 1104]. ZT values as high as ~2.4 and ~1.7 were measured for p/n-V2VI3-superlattices. Unfortunately exclusively these few data exsist, in spite of the fact, that this publication was path breaking for the field of thermoelectrics. There are several important questions still open which should be answered within the common project:

  • How does the structural perfection influence the thermoelectric characteristics?
  • Are the V2VI3-superlattices thermally stable and is the thermal stability identical for p- and n-type material?
  • Is the sequence in the work of Venkatasubramanian the best with respect to highest ZT values?
  • Is the well known anisotropy of V2VI3-compounds stable in those superlattices?
  • How differing the results of a complete thermoelectric characterisation applying in-plane and cross-plane measurement set-up using the same sample?

TEM studies will be used to characterize the superlattices with atomic resolution and determine the real-structure property relations. Structural changes of the superlattices will be detected during annealing by in-situ TEM. Compositional fluctuations on the nanoscale should be clarified by means of state-of-the-art electron spectroscopy with GIF/EFTEM. In a combined approach the structure will be characterized with X-ray methods.