2 research outputs found
Silicon-Based Thermoelectrics Made from a Boron-Doped Silicon Dioxide Nanocomposite
We report a method for preparing
p-type silicon germanium bulk
alloys directly from a boron-doped silica germania nanocomposite.
This is the first successful attempt to produce and characterize the
thermoelectric properties of SiGe-based thermoelectric materials prepared
at temperatures below the alloy’s melting point through a magnesiothermic
reduction of the silica-germania nanocomposite. We observe a thermoelectric
power factor that is competitive with the literature record obtained
for high energy ball milled nanocomposites. The large grain size in
our hot pressed samples limits the thermoelectric figure of merit
to 0.5 at 800 °C for an optimally doped Si<sub>80</sub>Ge<sub>20</sub> alloy
Rapid Microwave Preparation of Thermoelectric TiNiSn and TiCoSb Half-Heusler Compounds
The 18-electron ternary intermetallic systems TiNiSn
and TiCoSb
are promising for applications as high-temperature thermoelectrics
and comprise earth-abundant, and relatively nontoxic elements. Heusler
and half-Heusler compounds are usually prepared by conventional solid
state methods involving arc-melting and annealing at high temperatures
for an extended period of time. Here, we report an energy-saving preparation
route using a domestic microwave oven, reducing the reaction time
significantly from more than a week to one minute. A microwave susceptor
material rapidly heats the elemental starting materials inside an
evacuated quartz tube resulting in near single phase compounds. The
initial preparation is followed by a densification step involving
hot-pressing, which reduces the amount of secondary phases, as verified
by synchrotron X-ray diffraction, leading to the desired half-Heusler
compounds, demonstrating that hot-pressing should be treated as part
of the preparative process. For TiNiSn, high thermoelectric power
factors of 2 mW/mK<sup>2</sup> at temperatures in the 700 to 800 K
range, and <i>zT</i> values of around 0.4 are found, with
the microwave-prepared sample displaying somewhat superior properties
to conventionally prepared half-Heuslers due to lower thermal conductivity.
The TiCoSb sample shows a lower thermoelectric figure of merit when
prepared using microwave methods because of a metallic second phase