Lead Telluride Tin Telluride

Author : Christopher M. Jaworski
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (289 download)

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Download or read book An Investigation Into Lead Telluride Lead Sulfide Composites and Bismuth Tin Telluride Alloys for Thermoelectric Applications written by Christopher M. Jaworski and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: With the global interest in cutting back dependence on non-renewable energy sources, the field of thermoelectricity has recently seen renewed interest. Additionally, several exciting breakthroughs in both nanoscale and bulk materials have led to increased figure of merit zT. Figure of merit is a indirect measurement of a material's thermoelectric efficiency; its ability to convert a thermal heat flux to electrical power, and vice versa. Material zT has been limited to approximately 1 since the 1950's; in the past decade there have been several reports of zT>1.4. The major drawback for the development of thermoelectric devices is historically low material efficiency. However, it has been predicted that only a zT=2 is necessary to reach widespread usage of thermoelectric materials. A high zT material requires high thermopower, low electrical resistivity, and low thermal conductivity. These three material parameters are all interrelated. Therefore, recent research has focused on decoupling these parameters from each other. In this thesis, the underlying theory that is necessary for characterizing thermoelectric materials is outlined. We investigate the zT increase in the material system PbTe-PbS that was achieved through nanoprecipitation of PbS rich regions in a bulk PbTe matrix. After performing a full galvanomagnetic and thermomagnetic characterization where electrical resistivity, Seebeck, Hall, and Nernst-Ettingshausen coefficients are measured we calculate Fermi level, carrier effective mass, and scattering parameter. The introduction of the second phase of PbS in PbTe does not lower the product S2[sigma] but is reported to reduce thermal conductivity. It is this decrease in thermal conductivity that leads to a gain in zT. The second system studied is Bi2Te3:Sn. It has been reported by Kulbachinskii that Sn possibly forms a resonant level in Bi2Te3, and in this thesis, we investigate this claim further. In order to do so, we calculate a Seebeck coefficient vs. carrier density (Pisarenko relation) for Bi2Te3 and confirm it with experimental and literature data. This relation is necessary to determine if one has modified the density of states of Bi2Te3 and increased thermopower over that of a similarly doped Bi2Te3 that has a normal energy dispersion relation. In addition to the galvanomagnetic and thermomagnetic measurements, Shubnikov-de Haas (SdH) measurements are performed at 1.9K. There is conflicting literature on possible interpretations of the SdH measurements, we follow both interpretations and report the results. In summary, we conclude that by doping Bi2Te3 to higher carrier densities, we could begin to dope the lower valence band thus leading to an increase in zT.