During the past decades, thermoelectric (TE) materials have received renewed attention for potential applications in power generation, waste heat harvesting and solid-state cooling/heating. With the introduction of new material systems and advanced preparation techniques, the performance of state-of-the-art candidate materials has been greatly improved. Oxide-based materials, as newcomers to this field, have attracted growing interests due to their low production cost, high thermal stability and low toxicity. In the present work, the author reports upon the following three oxides with complex crystal structures, with emphasis on the synthesis techniques and transport property study. In delafossite-type copper aluminum oxide (CuAlO2), magnesium was used as the dopant to substitute aluminum atoms to improve the compound's high temperature performance. Powder processing and advanced sintering techniques were employed to fabricate bulk samples. Characterization results showed simultaneous improvement in the electrical and thermal properties of hot-pressed samples. Sodium-rich sodium cobalt oxide (NaxCoO2) was investigated for structural study and thermoelectric characterization. Both wet-chemical and electrochemical techniques were adopted to intercalate sodium ions into the compound, which is expected to improve cryogenic TE performance. Starting from the setup of Na battery, a in-situ Seebeck coefficient measuring system was proposed, based on the fact that precise sodium concentration control was successfully achieved. The focus of calcium cobalt oxide (Ca3Co4O 9) is to develop an innovative synthesis approach. Using agarose as a template, a sol-gel chemistry route involving mild acetates salt were developed. Comparing to traditional solid-state reaction, finer product particles, lower reaction temperature and more effective doping were achieved. Stoichiometric and Yb-doped samples were successfully prepared and characterized. Our study confirmed that oxides are a promising category of materials for a wide range of thermoelectric applications. Even though they are not as sophisticated as traditional TE materials at present, they showed great potential and interesting physical properties that would attract interests towards future research.
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