| The thermoelectric phenomena, the history and the recent development progress of thermoelectric materials were reviewed in detailed at first.We have selected calcium cobalt oxide(Ca3Co2Oo6) 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. To the part of Slack's theory, the oxide thermoelectric material calcium cobalt oxide(Ca3Co2O6) is a "phonon glass and an electron crystal" or PGEC. It has lower carrier mobility which enhanced by temperature. The phonon mean free path is lower than lattice parameters. So it has low electrical conductivity and low thermal conductivity.In this thesis, We prepared the sample through the method of sol-gel, sintered the nano-meter powders by spark plasma sintering. We have made an analysis on the thermoelectric properties such as the seebeck coefficient and electrical conductivity of the samples with doped different elements such as Na and Ni.For calcium cobalt oxide(Ca3Co2O6) which is a P-type semiconductor, the thermoelectric properties is as good as other Co-based oxide thermoelectric materials. At 700k, the dimensionless figure of merit ZT of the pure calcium cobalt oxide(Ca3Co2O6) can be as high as 0.15. With doped Ni element, the material converted into N-type semiconductor, what's more it has very low seebeck coefficient which shows Ni is +4 in this material. But when we doped Na element, the carrier density of the material ascended, and the electrical conductivity of the sample made improvements, its resistivity has up to 10-3 at 600k. Different Na doped have different result, so the stoichiometric ratio 2:1 of between Na element and Ca element in our research has the best properties, and the dimensionless figure of merit can be up to 0.3.The result in our thesis is a part of the oxide system, which reveals the is a promising material. Once it has good doped element, the probability of improvements exists. |
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