Abstract
In order to improve the thermoelectric conversion efficiency and figure of merit, ZT, composite materials of organic or inorganic constituents often are considered. The limitation of this approach is set by the effective medium theory, which states that the ZT in a composite material cannot exceed the greatest value of any single constituent, if the constituents do not interact. Here, we describe a method that circumvents this limit, based on the introduction of interfacial doping. An electrically and thermally insulating medium is distributed into a conventional thermoelectric host material but is coated with an aliovalent acceptor that is allowed to diffuse locally into the host matrix, thereby doping it locally. The thermal conductivity decreases when the insulating material is added, but the more electrically conducting region around the insulator prevents an equally large increase in electrical resistivity. Employing this method in p-type (Bi1-xSbx)2Te3 compounds results in a maximum figure of merit zT = 1.3, an over 10% improvement compared to the host material alone. We report synthesis and measurement techniques in addition to thermoelectric transport properties. While we report on one material system, the concept is not specific to that system and may be used to provide functionality in other thermoelectric composites.
Highlights
Due to their all-solid-state operation, thermoelectric coolers based on the Peltier effect have many positive attributes: they require no regular maintenance, produce no vibrations, emit no greenhouse gasses, offer a high specific cooling capacity, and scale well to low power and small size
We deployed silica beads with a coating made from an elemental metal known to be an aliovalent acceptor in (Bi0.25Sb0.25)2Te3 into the host
The coated beads were introduced in the (Bi0.25Sb0.25)2Te3 host matrix at various concentrations, and the elements (Pb or Ag) subsequently were allowed to diffuse
Summary
Due to their all-solid-state operation, thermoelectric coolers based on the Peltier effect have many positive attributes: they require no regular maintenance, produce no vibrations, emit no greenhouse gasses, offer a high specific cooling capacity, and scale well to low power and small size. In this case the model predicts that the power factor will rise, but the thermal conductivity will rise congruently, again resulting in a ZT that is unaffected.
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