All-Oxide Modules

Other pairs of cobaltite and perovskite nickelate as n-type have been assembled in modules where the electrical contacts were made by using silver paste charged with a powder of these oxides to improve the electrical contacts. With one pair of these materials, a power of 80 mW was delivered for a 500 K gradient. Larger output power values, reaching 340 mW have been also obtained by using more pairs. 

Although these points create severe limitations for short-term applications, the test of all-oxide modules has proved that large AT gradients up to 600 K can be applied on such modules, and, interestingly, that the performances of these TEG are reproducible after several cycles. Many research groups are putting efforts in this field. 

In this chapter, we have tried to give an overview on the emerging field of thermoelectric (TE) oxides. Dealing with this class of materials, the first important conclusion lies in the physics difference between the p- and n-type TE oxides. As a large part of that research has been devoted to the p-type NaxCo02 layer cobaltates and derived phases, one major output lies in the important role played by the electronic correlations. Usually the physics of conventional TEs is based on models of degenerate semiconductors and thus strongly correlated materials have opened new perspectives for the search of TE materials. 

The cobaltates behave as mixed-valent heavy fermions, with two bands, broad and narrow, responsible for the metallicity and large Seebeck coefficients, respectively. The origin of the coexistence of these localised spins and itinerant carriers is still under investigation, but this possible decoupling is very promising to optimise the TE properties. 

Finally, the possibility to create artificial superlattices to control the thickness of the conducting layer in order to take advantage of the S increase with the structure dimensionality decrease is also a promising route to enhance the figure of merit of oxides. This should help the solid state scientist in designing bulk TE oxides to use in TEG of the future. 

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