Study On Preparation And Property Of Cobaltite Oxides Based Thermoelectric Ceramics

Thermoelectric material is a kind of special functional material, which can drive the conversion between thermal and electrical energy based on the Seebeck, Peltier and Thomson effects. Considering the complex based Sol-Gel preparation and thermoelectric properties of Ca₃Co₄O₉ series compounds, this paper mainly carried out following studies: (1) exploring the preparation of Ca₃Co₄O₉ and its ceramic bulk using ethylenediaminetetraacetic acid (EDTA) as complex and discussing the effects of preparation conditions (such as heat treatment temperature) on the microstructure and composition of Ca₃Co₄O₉ samples through modern analysis and measurement techniques; (2) studying the preparation techniques of Ca3-xSmxCo4O9 and Ca3(Col-xZnx)4O9 on the basis of Sm and Zn doping, and the effects of heat treatment temperature on their microstructures; (3) Studying the effects of Sm and Zn doping on thermal and electrical conductivity by electrochemical impedance technique.During the complex based Sol-Gel preparation of Ca₃Co₄O₉ thermoelectric materials in aqueous solution, the amount and pH of the precursor sol and the calcination temperature can affect the purity of the designated products dramatically. The confirmed preparation condition in this study is as follows: molar ratio of the metal ion and complex was 1:1.5; pH value of the sol was 5⁶; the maintained temperature of designated products was 700 oC. An endothermic peak can be found at 700 oC in the differential thermal analysis(DTA)result, indicating the formation of Ca₃Co₄O₉ phase. X-Ray Diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX) and Fourier Transform Infrared Spectroscopy (FT-IR) results proved the high purity of the samples. The conditions for fabricating Ca₃Co₄O₉ ceramic bulk were also discussed and the optimized one is as follows: the pressure from the tablet press was 20 MPa, calcination temperature was 800 oC and holding time was 6 hours. Similarity, the confirmed optimized preparation conditions of series Sm/Zn doped Ca3-xSmxCo4O9 and Ca3(Col-xZnx)4O9 thermoelectric materials were confirmed.The electrical and thermal conductivity measurements based on the electrochemical impedance technique suggested that the electrical conductivity can be improved with increasing the temperature and Sm-doped amount for Ca3-xSmxCo4O9 system. Similarity, as far as Ca3(Col-xZnx)4O9 system was concerned, the Zn-doping with appropriate amount can improve the electrical conductivity and meanwhile abate thermal conductivity apparently.