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Thermoelectric materials thermoelectric effect is achieved through the material conversion between heat and electricity as a functional material, because of its environmental, energy and material use, and other areas, materials thermoelectric materials become a popular research direction. This article first thermoelectric phenomena, the history of development of thermoelectric materials, thermoelectric effects applications, such as thermoelectric materials research made a more detailed overview. In this paper, Ca 3 Co 4 O 9 as the research object, AR Co (NO 3 ) 2 · 6H 2 O, Ca (NO 3 ) 2 · 4H 2 O, citric acid as raw materials by sol - gel method (Sol-gel) system of Ca 3 Co 4 O 9 precursor powders with pressureless sintering method successfully prepared single-phase Ca 3 Co 4 O 9 materials. By XRD, optical microscopy, SEM, EDX, Archimedes, etc. on the prepared sample phase composition, microstructure, elemental composition, density, porosity, etc. are analyzed; and the testing and analysis of the sample resistance and thermal conductivity. Meanwhile, the sol - gel preparation of Ca 3 Co 4 O 9 sample with conventional solid-phase synthesis prepared Ca 3 Co 4 O 9 samples were analyzed. The results showed that: Ca 3 Co 4 O 9 material lamellar structure. In our experimental conditions, T 1 ~ T 3 temperature range, n 1 ~ n 4 citric acid with than the concentration range, t 1 ~ t 2 sintering time can generate Ca 3 Co 4 O 9 phase. Best preparation process: pre-firing process 2, n 1 concentration ratio, T 2 sintering temperature, t 2 sintering time. Citric acid concentration ratio, sintering temperature, sintering time and other parameters of the sample microstructure and thermoelectric properties has important implications: the same ratio of the concentration under the same sintering time appropriately increasing the sintering temperature is conducive to tissue growth; appropriate concentration ratio help to reduce the sintering temperature increased to shorten the sintering time; sintering at the same time the same concentration ratio, with the sintering temperature, the sample resistance substantially decreases, the thermal conductivity increases: the same sintering temperature is the same sintering time, as the concentration ratio increases, the sample resistance at first decreases and then increases the trend, the thermal conductivity decreases. Sol - gel method of Ca 3 Co 4 O 9 more traditional solid phase prepared Ca 3 Co 4 O 9 in the microscopic structure of the above have greatly improved. Sol - gel preparation of the sample particle size mostly in the 1 ~ 2μm between the pore distribution is uniform. Samples prepared by solid particle sizes vary greatly in the size range between 1 ~ 10μm, pore distribution is uneven. In Ag, Cr as the doping element, the system of the microstructure of the samples, to explore its electrical properties, etc. The results show: the microstructure of the samples doped, has a great impact on electrical performance, these two mixed miscellaneous agents can be improved to varying degrees, the thermoelectric properties of materials, and the doping is not the bigger the better, but the performance of the best doping.
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