Nagu, Manikanda Prabu
Synthesis and thermoelectric studies of Zintl phases in the systems of Ba-Al-Sb, Ba-Ga-Sb, and Ba-In-Sb.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2014)
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|Item Type:||Ph.D. Thesis|
|Title:||Synthesis and thermoelectric studies of Zintl phases in the systems of Ba-Al-Sb, Ba-Ga-Sb, and Ba-In-Sb|
Zintl phases have attracted interest due to their physical properties, electronic and crystal structures. In recent years ternary Zintl phases were being studied for their interesting thermoelectric properties. Though many Zintl phases are known, the compounds discussed in this work were not studied extensively before. This work emphasizes ternary Zintl phases containing barium and antimony. Ba3AlSb3, Ba3GaSb3, Ba7Ga4Sb9, BaGa2Sb2, and Ba5In2Sb6 have been investigated. In this work, ternary Zintl phases were prepared with optimized synthetic routes and characterized. DFT was used to calculate band gaps, according to which Ba3AlSb3 and Ba3GaSb3 are expected to be semiconductors and Ba7Ga4Sb9, BaGa2Sb2 and Ba5In2Sb6 should be metallic.
Spark plasma sintering was used to compact the products of high-temperature reactions of the elements to make pellets for thermoelectric measurements. Ba3AlSb3 exhibits high Seebeck coefficients (αmax = 383 µVK-1 at 342 K), low electrical (σmax = 18 Sm-1 at 342 K) and thermal conductivities (Κmin = 0.75 Wm-1K-1 at 342 K). Ba3GaSb3 also shows high Seebeck coefficients, low electrical and thermal conductivities. ZT values of both compounds were found to be low due to very low electrical conductivities. To modify the properties doping was attempted using zinc, calcium and strontium as dopants. The products were analysed to identify the presence of dopants using energy dispersive X-ray spectroscopy and atomic absorption spectroscopy. As an example, the thermoelectric properties of Ba3Al0.97Zn0.03Sb3 were studied. It shows modified properties and a higher figure of merit (ZTmax = 0.1081 at 490 K) than the undoped Ba3AlSb3. The thermoelectric properties of Ba7Ga4Sb9 could not be studied due to lack of thermal stability. BaGa2Sb2 was found to be stable in air. It shows high Seebeck coefficients, low electrical and thermal conductivities. Ba5In2Sb6 was found to be an n-type semiconductor. Ba5In2Sb6 exhibits low Seebeck coefficients (αmin = -74 µVK-1 at 473 K), low electrical (σmax = 12,955 Sm-1 at 683 K) and thermal conductivities (Κmin = 1.73 Wm-1K-1 at 520 K). The ZT values of BaGa2Sb2 and Ba5In2Sb6 were also found to be low.
|Place of Publication:||Darmstadt|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 540 Chemie|
|Divisions:||07 Fachbereich Chemie
07 Fachbereich Chemie > Fachgebiet Anorganische Chemie
|Date Deposited:||11 Dec 2014 13:54|
|Last Modified:||11 Dec 2014 13:54|
|Referees:||Albert, Prof. Dr. Barbara|
|Refereed:||3 November 2014|