Sol - Gel Preparation Of Ca <sub> 3 </ Sub> The Co. <sub> 4 </ Sub> O <sub> 9 </ Sub> Thermoelectric Materials,

Thermoelectric material is a functional material that realizes the exchange between thermal energy and electrical energy. Thermoelectric material is becoming a topical research aspect because of the ascendancies in the environment, energies and the utilization of materials. In this work,.the thermoelectric phenomena, the history, the use and the recent development progress of thermoelectric materials are reviewed in detailed at first.We have selected calcium cobalt oxide (Ca₃Co₄O₉) as our research object, which is a layered compound consisting of the alternate stack of CoO₂ layer which is responsible for the electric conduction and the insulated layer. Traditionally, the thermoelectric oxides can be fabricated by solid reaction method, but the whole process usually needs very long time, and it is easy to make the reactants become impure and inhomogeneous during preparing the samples. These problems result in sintering slowly, and getting good material performances difficultly. To be compared, the sol-gel method can get rid of these flaws.In the experiments, analytically pure Co(NO₃)₂·6H₂O, Ca(NO₃)₂·4H₂O and citric acid were used as raw materials, Ca₃Co₄O₉ samples were fabricated by sol-gel method. The microstructures of the samples were characterized by XRD, SEM, EDX et al. The relative density and pore number were measured too. The thermoelectric properties were determined by measuring electrical resistivity and thermal conductivity. At the same time, we prepared Ca₃Co₄O₉ samples by traditional solid reaction method too, which were contrasted with the samples prepared by sol-gel method.The results show that Ca₃Co₄O₉ ceramics contain random-oriented plate-shaped grains with layered structure. In the experiments, Ca₃Co₄O₉ phase formation sintering temperature, citric acid proportion and sintering time extent are in the region of T1^T3, n₁ⁿ₄ and t₁^t₂ respective. The best technique is sintering t₁ at T₂ in n₁. The technological parameters, such as citric acid proportion, sintering temperature, sintering time and so on, influence the microstructures and thermoelectric properties greatly. It is advantaged for the crystal growth when increase the sintering temperature reasonably in the same citric acid proportion and sintering time. And the reasonable increasing of the citric acid proportion...