Exploration and Optimization of Tellurium‐Based Thermoelectrics

For example, if Bi2Te3 is the powder, X must form intermediates with both Bi and Te for the reaction to
work. Typically halogens can achieve this; the solid halogen I2 as well as Cl2 gas – generated, in this case
from powdered TeCl4 – were both utilized in this work to achieve crystal growth from powders; to avoid
Te contamination, TeCl4 (thus Cl2 CVD) was saved only for reactions designed to contain Te. Typically a
small quantity of X(g), on the order of 5 – 10 mole percent, is utilized in the reaction to avoid the
formation of undesirable iodides or chlorides or cracking of reaction tubes from thermal expansion.
3.4. Arc Melting Reactions
Because many transition metals – in the case of this work, namely exploratory syntheses – have
melting points on the order of thousands of degrees Kelvin, a typical solid state reaction on the order of
923 or 1073 K may be insufficient to react the elements, depending on their melting point – even if
some ingredients are in a molten state. Producing a massive amount of current from a generator, an arc
of argon plasma is created in a chamber filled with the solids to be melted. The resultant electric arc is
capable of producing temperatures around 2773 K in seconds. Due to the volatility of many of the
studied elements such as Sb or Te, this procedure is not recommended when said powders are in their
elemental forms; in this case, excess powder should be used to offset the loss. Generally, a sample that
is to be arc‐melted is first placed in a resistance furnace between 773 – 1073 K to form a series of binary
compounds. After pressing the sample into a cylindrical (8mm diameter) pellet, it is arc melted for
seconds; enough to minimize any stoichiometry losses whilst still initializing the high‐temperature
reaction. This homemade setup is displayed in Figure 3.4.
Figure 3.4 Arc‐melting setup.
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