Thermoelectric Materials and Devices - Hierarchical Nanostructures for Energy Devices - page 122

d n 3 r 4 n g | 7

Figure 6.11 (a) Schematic of phonon scattering by various scales of hierarchical

structures. (b) Scanning TEM image showing the presence of SrTe
nanostructures in the PbTe matrix. The inset is the energy dispersion
X-ray spectrum (black, precipitate; blue, matrix). The histogram shows
the concentration profiles of Pb, Te, Sr and Na across the interface of
the large SrTe precipitate. (c) Figure of merit of Na-doped PbTe-SrTe
with various SrTe concentrations.
Reprinted with permission from Ref. 51. Copyright r 2012 Nature
Publishing Group.

.

6.3 Material Synthesis

6.3.1 Conventional Synthesis Schemes
Traditional bulk thermoelectric materials such as Bi 2 Te 3 , PbTe and SiGe
have been intensively studied in the last few decades. All of them are alloys
because alloys have low thermal conductivity, as we mentioned in the pre-
vious sections. Researchers obtain superior thermoelectric performance
with these materials by adjusting the synthesis methods, optimizing the
composition, and so on. These traditional thermoelectric materials have
been made by conventional alloy synthesis methods, which are very useful
because of their simple processes and ease of control. Here we introduce two
commonly used synthesis methods: 'melting and quenching' and 'mech-
anical alloying' (MA).