Exploration and Optimization of Tellurium‐Based Thermoelectrics

eported that another ternary in this system, TlSbTe2, also undergoes a phase transition – albeit at low
temperatures. [254] Several unsuccessful attempts involving high‐temperature XRD were also
endeavoured to further pursue this issue, but due to sample oxidation and additional noise from the
furnace, no reliable data could be produced. Quenching experiments in attempt to freeze the sample’s
state above this temperature are currently underway to learn if there is an identifiable high‐
temperature phase for the Sb compounds.
13.3.3.3. Low‐Temperature Physical Properties of Tl9TtxSb1‐xTe6
Due to the phase transition’s effect on the pellet quality and stability, samples were required to
be reproduced and annealed up to 473 K instead. Unfortunately, this lowers the functional temperature
for this material, therefore projecting that it may not be as useful as Tl9BiTe6 due to the temperature
ranges; lower annealing temperature also drops the magnitude of σ. Take for example Tl9Sn0.5Sb0.5Te6
which initially showed a value of 727 ‐1 cm ‐1 , dropping to 575 ‐1 cm ‐1 at room temperature. Likewise,
measurements on Tl9SbTe6 initially showed 874 ‐1 cm ‐1 to 429 ‐1 cm ‐1 at room temperature –a loss of
50 %. The systems however, show a more realistic trend in this lower temperature range, as depicted in
Figure 13.4. With both of the measured series, one observes the generic increase of S with increasing
temperature as expected for this family of compounds. All samples now show an overall increase in S
with decreasing x values, from 42 V∙K ‐1 at room temperature with Tl9Pb0.5Sb0.5Te6 to 86 V∙K ‐1 at room
temperature with Tl9Sn0.1Sb0.9Te6. It can be seen in the image that both series fall between the Seebeck
values of the respective ternaries. Though values can be slightly more erratic due to the low annealing
temperatures, this case demonstrates the system’s ability to form the expected trend through
modifications in x.
Figure 13.4 Low‐temperature ZEM measurements for Tl 9Tt xSb 1‐xTe 6:
Seebeck coefficient and electrical conductivity (left) and power factor (right)
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