Page 381 - Book Hosokawa Nanoparticle Technology Handbook

6.4 ELECTRIC PROPERTIES FUNDAMENTALS
Z is called “Thermoelectric Figure of Merit typical thermoelectric material used in Peltier cool-
(FOM)” and is an important performance measure of ing module, is known around 0.003 K 1 at room tem-
thermoelectric materials. It has a unit of inverse tem- perature; on the other hand, Si Ge 20 alloy has a Z
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1
perature (K ). value around 0.0008 K 1 at 1,000 K. Fig. 6.4.15
Since the thermoelectric effects are reversible phe- shows thermoelectric properties of polycrystalline
nomena, the electrical-to-thermal energy conversion Si Ge alloy measured from 300 to 1,300 K [2].
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5
has a similar configuration as shown in Fig. 6.4.14b. In
this case, the thermoelectric materials work as a solid- 6.4.3.1 Measurement method for thermoelectric
state heat pump operated by an external electric cur- materials
rent source. The maximum heat transfer from the low
temperature to high temperature side at specific power Practically, the thermoelectric properties , S and ,
consumption is called as “Coefficient of Performance should be evaluated with a same sample to determine
(COP),” and can be expressed as follows [1]. the Z value, because we cannot expect uniformity
among samples. The details to measure the electrical
conductivity and thermal properties are mentioned in
Q T 1 ZT ave T T L the Sections 6.4.2 and 6.3.1, respectively. References
H
IN L (6.4.11) on the measurement techniques for thermoelectric
P IN T H T L 1 ZT ave 1 materials are available at Japanese Industrial Standard
(JIS), such as JIS-R-1650-1 (Seebeck coefficient),
As seen in equations (6.4.10) and (6.4.11), an evalua- 1650-2 (Electrical resistivity), 1650-3 (thermal con-
tion of Z (or dimensionless value ZT ) is of importance ductivity).
in thermoelectric energy conversion applications, In this section, the principles of measuring impor-
which require the measurement of , S and of a tant physical properties of thermoelectric materials,
sample at a specific range of temperatures. For exam- such as Seebeck coefficient and Figure of Merit, are
ples, Z value for (Bi Te ) (Sb Te ) (x 0.7–0.9), outlined.
2
3 1 x
2
3 x

Figure 6.4.15
Thermoelectric properties of SiGe alloy [2]. (a) The electrical resistivity (inverse electrical conductivity ), (b) the
Seebeck coefficient S, (c) thermal conductivity and (d) the thermoelectric Figure of Merit Z. Open circles, filled
circles, filled square and filled triangle correspond to P-doped Si Ge , P/GaP doped Si Ge , Si Ge , respectively.
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