| dc.description.abstract | The high performance thermoelectric material tin selenide is of notable interest to the field of thermoelectric materials; since breaking the record for being the most efficient thermoelectric material due to the ultralow thermal conductivity. These materials have many potential and current applications such as radioisotope generators, waste heat recovery in vehicles, power generation, sensors, and refrigeration.
The optimization of the thermoelectric properties of p-type double doped tin selenide, and n-type double doped tin selenide have been investigated through the course of this thesis project. The experimental synthesis parameters have been thoroughly investigated to determine a consistent, optimized procedure for the production of polycrystalline tin selenide thermoelectric materials. The key components of the optimized synthesis procedure include, cooling method from melt synthesis (water quenching), preparation before hot pressing (ball milling 600 rpm, 6 hours), reduction (773 K, 8 hours, 5 % H2/Ar), and hot pressing parameters (773 K, 48 MPa, 10 min).
Using consistent synthesis methods, the optimization of the composition for the double doped p-type, and n-type samples was determined by using a triangulated 3-dimensional surface plot for each of the systems. The p-type system NaxCuySn1-x-ySe (0≤x≤0.035), (0≤y≤0.016) had two compositions of interest with notably high average and peak thermoelectric figure of merit (ZT) Na0.034Cu0.016Sn0.961Se (0.45, 0.96), Na0.0113Cu0.0077Sn0.978Se (0.45, 0.77) between 298 K and 773 K, low minimum thermal conductivities (K) of (0.36 W m-1 K-1 ), (0.45 W m-1 K-1 ), and peak electrical conductivity (σ ) (132 S cm-1 at 420 K), (239 S cm-1 at 323 K) respectively. The n-type system Sn1-xBixSe1-yBry (0≤x≤0.06), (0≤y≤0.06) had a composition of interest with notably high peak and average thermoelectric figure of merit (zT) (0.57 at 773 K, 0.21 from 298 K to 773 K), low minimum thermal conductivity (0.48 W m-1 K-1 ), and power factor (3.66 μW cm-1 K-2) for SnSe0.94Br0.06 .
Finally using the fully optimized procedure and compositions three high performance p-type, and two n-type polycrystalline tin selenide samples were prepared with the compositions; Na0.033Cu0.015Sn0.96Se, Na0.033Ag0.015Sn0.96Se, Na0.034Au0.015Sn0.96Se, SnSe0.94Br0.06, SnSe0.94Cl0.06.
All five samples were prepared using identical sources of tin, and were prepared in parallel to ensure comparison between the different dopants can be consistently determined.
The highest performance p-type sample was Na0.033Ag0.016Sn0.963Se, with a maximum zT of 2.12 at 910 K, an average zT of 0.87 from 298 K to 910 K, minimum thermal conductivity of 0.24 W m-1 K-1 at 910 K and peak power factor of 6.01 μW cm-1 K-2 at 468-516 K.
The highest performance n-type sample was SnSe0.9Br0.1, with a maximum zT of 0.77 at 910 K, and an average zT of 0.34 from 298 K to 910 K, minimum thermal conductivity of 0.49 W m-1 K-1 at 811 K and peak power factor of 4.89 μW cm-1 K-2 at 910 K. | en |
