Exploration and Optimization of Tellurium‐Based Thermoelectrics

5.1. Power Factor Measurements: ZEM‐3 Instrument
The numerator of , , is known as the Power Factor and is the product of the Seebeck
coefficient squared and the electrical conductivity. The ULVAC‐RIKO ZEM‐3 setup is the most frequently
used instrument in the Kleinke group at this time, due to simultaneous measurement of S and σ over a
wide temperature range – generally between ambient temperature and 673 K in this work because
conventionally, materials are examined 100 K below their melting point to ensure the machine is not
affected by melting compounds or vaporizing elements.
Figure 5.1 (a) ULVAC ZEM‐3 (left) ZEM schematic (right)
Pellets for the ZEM must have a minimum of 6 mm length in order to be properly measured by the
horizontal probes displayed in Figure 5.1 (b), which are capable of 3, 5 or 8 mm separations. The four
visible points of contact in the ZEM pellet mount are displayed in Figure 5.1 (b) along with conceptual
representation of the instrument’s functionality. A digital microscopic camera (Dino‐lite plus, AnMo
Electronics Co.) and analysis software is used to obtain accurate measurements of pellet dimensions and
probe separations along with the Vernier calliper initially used to measure pellets.
The Seebeck coefficient, S, is simply defined in Chapter 1 as ∆
. This is achieved by the
instrument creating a temperature difference between the platinum‐iridium thermocouples, then
measuring the voltage difference ∆ utilizing the same probes. ∆ is created by taking the average of
three manually input temperature targets for the internal platinum heater (Figure 5.1 (b)) which in this
case are set to ‘10’, ‘15’ and ‘20’ K, leading to ~2‐3, ~3‐4 and ~4‐5 degree differences above the target
ambient temperature respectively. This leaves enough space between measured values for the
system to create a reasonable line‐of‐best‐fit such that this slope becomes the measured ∆ taken to
achieve the experimental values at each .
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∆