Exploration and Optimization of Tellurium‐Based Thermoelectrics

scientist Heinrich Emil Lenz (1804 – 1865) demonstrated that Peltier’s temperature difference could be
reversed if the current were reversed. The Peltier coefficient thusly describes the ratio of heat flow,
, to current applied, , in the form Π
. Following the discovery of the Seebeck and Peltier Effects,
William Thompson (Figure 1.2 (c)) or Lord Kelvin, in 1852 succeeded in proving the existence of a
relationship between Seebeck’s and Peltier’s phenomena. That is,
.[8] This demonstrates that the
properties discovered separately are in fact united as a single concept of thermoelectric effects.
While the effects were known and in part studied for the purpose of research, the field
remained relatively dormant until the 1930s evolved Strutt’s electron band theory of crystals [9] and a
keen interest by William Ioffe lead to proof that a semiconductor‐based thermoelectric generator could
achieve an efficiency (η) of approximately 4 %. [10] In the 1950s and 1960s, the study of the key materials
PbS and PbTe and their thermal conductivity [11] kept the field active. The next major discovery in
thermoelectrics was work by Glen Slack in the late 1970s regarding thermal conductivity of non‐metallic
crystals and the concept of materials reaching a thermal conductivity minimum at some temperature [12]
(i.e. reduction of all thermal transport except lattice vibrations). This work lead to performance limits
and eventually evolved into an idealized notion of a material with the thermal conductivity of a glass
and the electrical conductivity of a crystal – phonon glass electron crystal (PGEC). [13]
1.2. Efficiency and the Thermoelectric Figure of Merit
Thermoelectric materials are evaluated in the field based on their dimensionless figure of merit,
or ZT. It allows researchers to quickly identify materials with good potential in the field and the
components of said material that make it promising. This figure allows for a quick and universally
understood classification of materials’ thermoelectric potential based on a few key properties displayed
below (Equation 1.1): S is the Seebeck coefficient, σ is the electrical conductivity and is the thermal
conductivity from both electronic and lattice (or phonon) contributions. represents the average
system temperature based on the hot and cold gradient temperatures:
.
Equation 1.1 Dimensionless figure of merit
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