Journal of Materials Research


Microstructures and nanostructures in long-term annealed AgPb18SbTe20 (LAST-18) compounds and their influence on the thermoelectric properties

Jayaram Daddaa1 c1, Eckhard Müllera1, Susanne Perlta2, Thomas Höchea2, Paula Bauer Pereiraa3 and Raphaël P. Hermanna3

a1 Institute of Materials Research, German Aerospace Center (DLR), D-51170 Köln, Germany

a2 Leibniz Institute of Surface Modification (IOM), D-04318 Leipzig, Germany

a3 Forschungszentrum Jülich GmbH, IFF, JNCS and JARA-FIT, D-52425 Jülich, Germany Faculty of Sciences, University of Liège, B-4000 Liège, Belgium


This article reports on the role of annealing on the development of microstructure and its concomitant effects on the thermoelectric properties of polycrystalline AgPbmSbTe2+m (m = 18, lead–antimony–silver–tellurium, LAST-18) compounds. The annealing temperature was varied by applying a gradient annealing method, where a 40-mm-long sample rod was heat treated in an axial temperature gradient spanning between 200 and 600 °C for 7 days. Transmission electron microscopy investigations revealed Ag2Te nanoparticles at a size of 20–250 nm in the matrix. A remarkable reduction in the thermal conductivity to as low as 0.8 W/mK was also recorded. The low thermal conductivity coupled with a large Seebeck coefficient of ∼320 μV/K led to high ZT of about 1.05 at 425 °C for the sample annealed at 505 °C. These results also demonstrate that samples annealed above 450 °C for long term are more thermally stable than those treated at lower temperatures.

(Received December 22 2010)

(Accepted April 20 2011)

Key Words:

  • Thermoelectricity;
  • Annealing;
  • Second phases


c1 Address all correspondence to this author. e-mail: