Abstract
In the field of thermoelectric energy conversion, oxide materials show promising potential due to their good stability in oxidizing environments. Hence, the influence of oxygen partial pressure during synthesis on the thermoelectric properties of Cu-Delafossites at high temperatures was investigated in this study. For these purposes, CuFeO2 powders were synthetized using a conventional mixed-oxide technique. X-ray diffraction (XRD) studies were conducted to determine the crystal structures of the delafossites associated with the oxygen content during the synthesis. Out of these powders, films with a thickness of about 25 µm were prepared by the relatively new aerosol-deposition (AD) coating technique. It is based on a room temperature impact consolidation process (RTIC) to deposit dense solid films of ceramic materials on various substrates without using a high-temperature step during the coating process. On these dense CuFeO2 films deposited on alumina substrates with electrode structures, the Seebeck coefficient and the electrical conductivity were measured as a function of temperature and oxygen partial pressure. We compared the thermoelectric properties of both standard processed and aerosol deposited CuFeO2 up to 900 °C and investigated the influence of oxygen partial pressure on the electrical conductivity, on the Seebeck coefficient and on the high temperature stability of CuFeO2. These studies may not only help to improve the thermoelectric material in the high-temperature case, but may also serve as an initial basis to establish a defect chemical model.
Highlights
IntroductionThermal energy can be directly converted into electrical energy
We evaluated the thermoelectric performance and the electrical conductivity of the delafossite-type oxide CuFeO2, as it depends on the oxygen partial pressure at high temperatures, and found some interesting properties, especially an as yet unknown p-n-transition
Since the oxygen partial pressure plays a decisive role during the synthesis and application of Delafossites, X-ray diffraction (XRD) studies confirmed that a lowly oxidizing calcination atmosphere is essential for the preparation of single phase CuFeO2
Summary
Thermal energy can be directly converted into electrical energy. We evaluated the thermoelectric performance and the electrical conductivity of the delafossite-type oxide CuFeO2 , as it depends on the oxygen partial pressure at high temperatures, and found some interesting properties, especially an as yet unknown p-n-transition. As the particles impact on the substrate, a dense layer forms by fracture and plastic deformation of the particles on the surface of the substrate [41,42,43,44] Using this method, thin CuFeO2 and dense layers were prepared to study the oxygen partial pressure dependence on the thermoelectric properties, to compare aerosol deposited. CuFeO2 with conventionally solid-state prepared CuFeO2 , and to deepen the understanding of their electrical conduction mechanism
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