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We have presented here direct proof that the AgPbmSbTem+2
samples do not behave as classical solid solutions between
AgSbTe2 and PbTe but exhibit nanoscopic inhomogeneities with
alarge range of structural features from atomic ordering, revealed
by single-crystal X-ray diffraction, to nanostructures
highlighted by electron diffraction and high-resolution imaging.
The superiorthermoelectric figure of merit in the LAST
materials by a large part originates from a lowering of the lattice
thermal conductivity. The presence of coherent, endotaxial,
nanosized islands that arerich in Ag-Sb embedded in a matrix
rich in Pb may be associated with the enhancement of the
thermoelectric properties encountered in the AgPbmSbTem+2
materials. One of the possible explanations forthe depression
of the thermal conductivity with simultaneous retention of a
high power factor is that these coherent nanocrystalline regions
possess different electronic and vibrational propertiesthan those
of the surrounding matrix leading to a sort of quantum
confinement and enhanced acoustic phonon scattering.32 From
these considerations it becomes apparent that the thermoelectricproperties of the LAST family of materials might be very
sensitive to the experimental conditions employed to prepare
them. If proper conditions prevail to allow these nanostructures
to develop we mayanticipate superior thermoelectric properties.
(32) (a) Hicks L. D.; Dresselhaus M. S. Phys. ReV. B 1993, 47, 12727-12731.
(b) Hicks L. D.; Harman T. C.; Dresselhaus M. S. Appl. Phys. Lett. 1993,63, 3230-3232. (c) Dresselhaus M. S.; Lin Y. M.; Cronin S. B.; Rabin
O.; Black M. R.; Dresselhaus G.; Koga T. Recent Trends In Thermoelectric
Materials Research Iii Semiconductors and Semimetals 2001,71, 1-121.
Figure 11. High-resolution image on a LAST-18 sample (a) showing the coexistence at the nanoscopic scale of two kinds of domains magnify in b and c
figures. The fast Fourier transforms...
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