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

Abstract

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, Weinhei

In2O3-Based Thermoelectric Materials: The State of the Art and the Role of Surface State in the Improvement of the Efficiency of Thermoelectric Conversion

“…However, the ZT of oxychalcogenides is restricted by their electrical resistivity. The low electrical conductivity is related to a low carrier concentration of 1 × 10 18 cm −3 and a carrier mobility of 22 cm 2 /V·s [68].…”

“…However, the ZT of oxychalcogenides is restricted by their electrical resistivity. The low electrical conductivity is related to a low carrier concentration of 1 × 10 18 cm −3 and a carrier mobility of 22 cm 2 /V·s [68]. In contrast, n-type oxides, demonstrating high TE performance comparable to p-type oxides, have not yet been developed, despite continuing efforts [18,33,69].…”

“…Information on other n-type oxides such as MnO 2 , WO x , V 2 O 5 , MoO x , Fe 2 O 3 , Cr 2 O 3 , and their various binary and ternary compounds such as Magneli phases and Ruddlesden-Popper phases, which were also tested as thermoelectric materials, can be found in [2,32,33,68]. It is important to note that all these metal oxides are inferior to the previously-considered oxides in their parameters.…”

Spark Plasma Sintering of Tungsten Oxides WOx (2.50 ≤ x ≤ 3): Phase Analysis and Thermoelectric Properties

“…By now, TMOs are subject of in-depth investigations [2][3][4] in particular because there is still a lack of appropriate n-type counterparts, although lanthanum-doped SrTiO 3 [5], ZnO [6] or doped TiO 2−x [7][8][9] show promising results.…”

“…An interesting approach is the exploitation of crystallographic shear (CS) for the reduction of the lattice thermal conductivity κ lat due to increased phonon scattering [4,10,11]. CS plane structures occur when a transition metal is partially reduced and oxygen layers are removed from the structure, e.g., of TiO 2 , VO 2 , MoO 3 and WO 3 .…”