Thermoelectric materials are highly important due to the ever-increasing demands for more eﬃcient and environmentally-friendly methods of energy production. They oﬀer enhanced energy eﬃciency across the industrial and automotive sectors through the harvesting of waste heat and conversion into electricity and are assessed by the ﬁgure of merit ZT = (S2σ/κ)T, which combines the Seebeck coeﬃcient (S), electrical conductivity (σ), thermal conductivity (κ) and temperature (T).
Strong coupling between the above properties limits the improvement of ZT. The electronic (σ and S) and thermal (κ) transport properties are strongly coupled making it notoriously diﬃcult to control them separately and maximise ZT through the design of new thermoelectric materials. An increase in σ, for example, would degrade S and increase the electronic component of κ, detrimental to ZT overall.
The decoupling of electronic and lattce transport, which allows for independent control over these properties has not yet been realised in oxide thermoelectrics.
A team at the University of Liverpool has successfully separated the thermal and electronic transport properties through the introduction of chemical disorder within an n-type thermoelectric oxide. This chemical disorder resulted in an intrinsically low κ, reduced by a factor of four over materials with the same structure type. The structural chemistry makes it possible to further dope the material using chemical substitution to independently tune the electronic properties whilst retaining the low κ. The ability to decouple the electronic and thermal transport is intrinsic to the material and structure, and is not a result of microstructure eﬀects.
- Decoupling of electronic and thermal transport within an oxide
- Reduced thermal conductivity is intrinsic to the material, and not a result of microstructure eﬀects
- Ability to independently inﬂuence the electronic and thermal properties through chemical substitution
- Low cost, low toxicity and superior chemical stability of oxide materials over classical intermetallics is a major advantage.
The University team has synthesised, characterised processed and measured dense ceramics of such materials in-house to explore the above concept.
Currently the team are investigating the applicability of this method to a broad range of materials.