Development of High performance Thermoelectrics

Development of High performance Thermoelectrics

Thermoelectric generators are solid state devices which convert heat into electricity (Seebeck effect). The use of solar radiation or waste heat from thermal combustion processes (e.g. machines, engines, and living beings) as energy source for a thermoelectric generator is an attractive and sustainable way to cover the increasing auxiliary electrical power demand.
In order to compete as energy converters, solid state thermoelectric generators must be more efficient and/or cheaper and lighter than the today’s systems. The research on thermoelectricity aims at the development and characterisation of novel materials suitable for the direct and efficient thermoelectric conversion of heat into electricity. The material should exhibit high stability, a large Seebeck coefficient, good electrical conductivity, and a small thermal conductivity. The challenge for the materials design is that these transport properties are interdependent- changing one alters the other-, making the optimization difficult.

The performance of a TE material is quantified by the dimensionless figure of merit ZT = a2sT/k, where a is the Seebeck coefficient (thermopower), σ the electrical conductivity, and k the thermal conductivity (in the simplest case k = ke + kph, where ke is the carrier thermal conductivity and kph the phonon thermal conductivity.). For convenience, a2s is called the power factor (PF). To date, degenerate semiconductors constitute the corner stone of state-of-the-art TE materials; and these materials have maximum ZT~1-2 in their respective temperature range of operation. Per the definition of ZT and in the context of G. Slack’s “phonon glass electron crystal” concept, the strategy of TE research is two-fold: (i) reducing the phonon thermal conductivity (kph) toward a “phonon glass”, while (ii) enhancing the power factor (PF) toward an “electron crystal”.

Our research focus on developing high performance thermoelectric materials by manipulating microstructure and composition, which control the phonon and electron transport properties. The research topics include:

·       Complex transition metal oxides (manganates, cobaltates, titanates),

·       Fe- and Ni based half Heusler materials,

·       inhomogeneous high temperature phases

·       2D materials: Chalcogenides

·       Nanostructured and hybride materials.