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
Compared to conventional deposition techniques for the epitaxial growth of metal oxide structures on a bulk metal substrate, wet-chemical synthesis based on a dispersible template offers advantages such as low cost, high throughput, and the capability to prepare metal/metal oxide nanostructures with controllable size and morphology. However, the synthesis of such organized multicomponent architectures is difficult because the size and morphology of the components are dictated by the interplay of interfacial strain and facet-specific reactivity. Here we show that solution-processable two-dimensional Pd nanotetrahedra and nanoplates can be used to direct the epitaxial growth of γ-Fe 2 O 3 nanorods. The interfacial strain at the Pd−γ-Fe 2 O 3 interface is minimized by the formation of an Fe x Pd "buffer phase" facilitating the growth of the nanorods. The γ-Fe 2 O 3 nanorods show a (111) orientation on the Pd(111) surface. Importantly, the Pd@γ-Fe 2 O 3 hybrid nanomaterials exhibit enhanced peroxidase activity compared to that of isolated Fe 2 O 3 nanorods with comparable surface area because of a synergistic effect for the charge separation and electron transport. The metal-templated epitaxial growth of nanostructures via wet-chemical reactions appears to be a promising strategy for the facile and high-yield synthesis of novel functional materials.
The synthesis and production of thermoelectrical active ceramic materials, the concepts of the module design by simulation, the assembly of modules by laser joining, and the investigations concerning the operation modes are described in this paper. Investigations of the material structure, the phase composition, and the thermoelectrical properties illustrate the material development. The newly developed technological route is described. The simulated results of thermoelectric modules for operational cases are compared with gained experimental data.
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