Exploration and Optimization of Tellurium‐Based Thermoelectrics

1.3.2. Advantages and Disadvantages
Like any device or material on the market, the good must be weighed against the bad. In the
case of TE materials, there are many wonderful advantages – many of which can be postulated from the
applications recently discussed. Possessing no moving or mechanical parts allows these materials to
function for a substantially long time without need for repair. Additionally, the lack of moving parts can
allow one to conclude that these devices are extremely quiet; compare a TE refrigerator to a standard
refrigerator, and the lack of a compressor leaves the TE device both quiet and light‐weight. Another
advantage that can be related to the applications is there are no bi‐products with TE devices such as
CFCs inside old refrigerators, or greenhouse gasses from combustion engines.
The major disadvantage of using TE materials is their low efficiency. A typical efficiency for a
combustion engine is between 30 and 45 % while thermoelectrics have been found to achieve between
2 and 12 % currently. The idea of efficiency will be further evolved in the following section in terms of
ZT information. Another consideration with respect to disadvantages of TE materials is the cost
involved. At this point the TEG alone is approximately $1200 USD, as is the module’s assembly; the total
cost is projected at $4800 USD (1 kW) or nearly $20,000 for a 5 kW system in the preliminary stages. [42]
It should also be noted that a TEG requires two TE semiconductor (p‐ and n‐) types, and the system is
only as efficient as its weakest material. Thus, one must assemble a device from the best p‐ and n‐ types
known.
1.3.3. State‐of‐the‐Art Materials
1.3.3.1. Chalcogenide Materials
The chalcogenides were the first TE materials to be studied with the intense thermoelectric push
of the late 1950s, where a significant topic of interest was the Bi2Te3 compound – a semiconductor that
could serve as both a p‐ and n‐ type material depending on whether the deficiencies were placed on the
Bi sites or on the Te sites. [4] With a layered structure (discussions within Section III), a high ZT value
near room temperature, and rampant opportunities for doping, this material is an understandable topic
of interest. From the mid‐1900s work commenced – much by Caillat et al. – on improving Bi2Te3’s
thermoelectric properties. From mixing it with Bi2Se3 or Sb2Te3 starting in the early ‘80s, [13] on to using
nanostructuring techniques around the late ‘90s, such as nanotube creation by Zhao et al. [43] Closely
following the work on Bi2Te3, were studies on other tellurides including PbTe – also having an extensive
array of studies such as doping, deficiencies, alloying, etc. Like PbTe, the closely related Te‐Sb‐Ge‐Ag
(TAGS), [44] which is a compound comprised of the four elements based on the solid solution
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