A chemists view: Metal oxides with adaptive structures for thermoelectric applications

Thermoelectric devices can help to tackle future challenges in the energy sector through the conversion of waste heat directly into usable electric energy. For a wide applicability low-cost materials with reasonable thermoelectric performances and cost-efficient preparation techniques are required. In this context metal oxides are an interesting class of materials because of their inherenthigh-temperature stability and relative high sustainability. Their thermoelectric performance, however, needs to be improved for wide application. Compounds with adaptive structures are a very interesting class of materials. A slight reduction of early transition metal oxides generates electrons as charge carriers and crystallographic shear planes as structure motif. The crystallographic shear planes lead to a reduction of intrinsic thermal conductivity. At the same time, the electronic transport properties can be tuned by the degree of reduction. So far only a few transition metal oxides with adaptive structures have been investigated with respect to their thermoelectric properties, leaving much room for improvement. This review gives an overview of thermoelectric oxides, highlights the structural aspects of the crystallographic shear planes and the resulting thermoelectric properties. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim