| Thermoelectric material is a kind of functional materials which can convert thermal energy directly into electricity mutually, and due to it’s special ability in the aspect of energy utilization and environmental protection, making it become the focus of material research field. Cobalt oxide materials exhibit better thermoelectric properties among oxide thermoelectric materials, more over their advantages such as non-toxic, environmental friendly and high temperature stability at high temperature attracted much attention of many researchers in recent years. RBa Co4O7 ceramic material is a new type of cobalt oxide material, belonging to the p type semiconductor material, possessing complicated lattice structure, higher Seebeck coefficient and lower thermal conductivity, exhibiting better thermoelectric properties at high temperature. Many previous studies show that metal elements of good conductive properties doping can often improve the performance of thermoelectric materials. Therefore, we hope that we can improve the thermoelectric properties of RBa Co4O7 ceramic materials through R site metal elements doping.The ceramic samples were synthesized by the traditional solid-state reaction method in this experiment. X-Ray diffraction(XRD) was employed to check the phase structures of the prepared samples and the influence of temperature and the content of doping elements on electrical resistivity, Seebeck coefficient, power factor, thermal conductivity and ZT value were investigated.First, the investigation of YBa Co4O7 ceramic doping was selected as the inquiry experiment due to the relatively cheap raw materials, and Ag、Pb、Sr、Tl、Zn、C u were chosen as the doping elements. The results show that more impurities phase were produced by higher proportion of elements doping, causing higher electrical resistivity, so the doping ratio is controlled at about 0.1 in this experiment. O n the whole, the selected doping elements significantly reduce the electrical resistivit y of the material, optimizing the thermoelectric properties of materia ls. The effect of different doping elements on the thermoelectric properties of materials is different due to the differences of ionic radius, electrical conductivity and atom mass of different doping elements. Among the selected doping elements, Ag and Pb doping have best effects on optimizing the thermoelectric properties of YBa Co4O7 ceramic materials. Specially, the optimum doping amount is 0.15 in Ag doping experiment, and the power factor of Y0.85Ag0.15 Ba Co4O7 samples reached a maximum value of 81μWm-1K-2 at 973 K, 72.7% higher than that of the undoped sample, at the same time, the ZT value can reach 0.125.The optimum doping elements of Ag and Pb which were filtered in the inquiry experiment were used to analyse its effect on Yb Ba Co4O7 ceramic materials. The results show that Pb doping have best effects on optimizing the thermoelectric properties of Yb Ba Co4O7 ceramic materials, and the power factor of Yb0.92Pb0.08 Ba Co4O7 samples can reach 84 μW m-1 K-2 at 973 K, 55% higher than that of the undoped sample, meanwhile, the ZT value reached 0.12, 69.5% higher than that of the undoped sample.Finally, the optimum doping elements of Ag and Pb which were filtered in the inquiry experiment were used to analyse its effect on Lu Ba Co4O7 ceramic materials. The results show that Pb doping have best effects on optimizing the thermoelectric properties of Lu Ba Co4O7 ceramic materials, and the power of Lu0.92Pb0.08 Ba Co4O7 samples can reach 85 μW m-1 K-2 at 973 K, 22.3% higher than that of the undoped sample, meanwhile, the ZT value reached 0.18.On the whole, the results show that: R site hole doping significantly reduces the resistivity of RBa Co4O7 ceramic materials, but also reduces the Seebeck coefficient of materials, while on the whole effect, the power factor of the material are improved in small proportion of doping due to the amplitudes of the electrical resistivity’s decrease greater than that of Seebeck coefficient’s. Among the selected doping elements, Ag and Pb doping have best effects on optimizing the thermoelectric properties of RBa Co4O7 materials, which is consistent with the doping effect on the most of oxides materials. |
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