Substitution studies in casium lead bismuth telluride and sodium lead antimony telluride for thermoelectric applications . Aurelie Gueguen

ISBN: 9781109237504

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228 pages


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Substitution studies in casium lead bismuth telluride and sodium lead antimony telluride for thermoelectric applications .  by  Aurelie Gueguen

Substitution studies in casium lead bismuth telluride and sodium lead antimony telluride for thermoelectric applications . by Aurelie Gueguen
| NOOKstudy eTextbook | PDF, EPUB, FB2, DjVu, audiobook, mp3, RTF | 228 pages | ISBN: 9781109237504 | 7.76 Mb

Thermoelectric devices convert thermal energy into electrical power or vice versa. If materials with thermoelectric figure of merit 3 can be synthesized, thermoelectric devices will not be restricted to niche applications such as spacecraft powerMoreThermoelectric devices convert thermal energy into electrical power or vice versa.

If materials with thermoelectric figure of merit ≥ 3 can be synthesized, thermoelectric devices will not be restricted to niche applications such as spacecraft power generation and will have a significant impact on the economy. Power generation from waste heat recovery would be an alternative energy resource whereas electronic cooling would significantly increase computing processor speed.

Good thermoelectric materials require high electrical conductivity, large thermopower and low thermal conductivity. Complex chalcogenides materials, such as CsBi4Te6, exhibit promising thermoelectric properties. It consists of Cs+ cations weakly bound to [Bi4Te 6]- layers.

The Cs+ cations act as rattlers, hence contributing to a reduction of the lattice thermal conductivity. Partial substitution of Bi by Pb resulted in the discovery of the homologous family CsPbmBi3Te5+m. Further substitution studies both on the Cs and Bi sites lead to the synthesis of the new compounds Cs 0.76K0.74Bi3.5Te6 (1), CsNa0.98Bi4.01Te7 (2), Cs 0.69Ca0.65Bi3.34Te6 (3), Rb0.82Pb0.82Bi3.18Te6 ( 4), Rb0.19K1.31Bi3.50Te6 (5), RbSnBi3Te6 (6), Rb 0.94Ca0.94Bi3.06Te6 (7), RbYbBi3Te6 (8) and KSnSb3Te 6 (9).

However synthesis conditions could not yet be optimized to prepared pure phase with good quality crystal.-Doped PbTe is used in commercial applications. Recent studies on preparation of bulk nanostructured PbTe have shown significant improvement in the thermoelectric figure of merit, achieved mainly through reduction of lattice thermal conductivity.

The observation by TEM of nanoprecipitates embedded in the PbTe matrix is believed to be the origin of their low thermal conductivity. A figure of merit ZT ∼ 1.6 at 650 K was reported for example for the p-type Na1-xPb mSbyTem+2 (SALT) system. Partial substitution of Pb by Sn was studied through the synthesis of the NaPb18-xSn xSbTe20 series and increases the carrier concentration.

As a result, an increase in electrical conductivity and a decrease in thermopower were observed with increasing amount of Sn. Such substitution did not affect the formation of nanoprecipitates, which were observed with TEM along with lamellar features. The substitutions did not result in higher figure of merit. Replacing Sb by Bi produced weaker samples.

The K analog series, KPb 18-xSnxSbTe20, was prepared as well and resulted in weaker and more water-sensitive specimens. These different studies show that the best p-type materials so far are Ag(Pb1-ySny) mSbTe2+m (LASTT) and Na1-xPbmSb yTem+2 (SALT) systems. Substituting Ag by Cu in the n-type AgPbmSbTem+2 (LAST) system resulted in phase segregation of Cu2Te and Sb2Te3 in the PbTe matrix. The figure of merit of the specimens was lower than that of LAST.



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