Preparation And The Thermoelectric Properties Of The BiTe Based Thermoelectric Materials

Thermoelectric materials are those materials that directly convert heat to electricity or conversely, which are prospect using as the thermoelectric generators and cooling devices that is small in sizes, without noises and without any pollutions of the environment. Bi2Te3 compounds and their solid solutions have received considerable attention due to their great potential for application in refrigeration, the figure of merit of which is about 1. In this paper, the new approaches have been applied to improve the performance of the BiTe-based alloys. Special consideration has been made on the alloying with the rare earth elements, since they have an unusual electronic state called the intermediate valence state. It is first time to synthesize the Bi2Te3-based rare earth intercalated compounds by mechanical alloying (MA) in the present work. Bi0.5Sb1.5Tes/Polyaniline composites were also prepared and studied aimed to develop the low thermal conductive inorganic/organic thermoelectric composites.It is shown the electrical conductivity of the MA alloys powders are small in grain size and uniform in element dispersion in comparing with melting alloys, however fine grain sizes result also in the lower electrical conductivity.The XRD analyses of the La15Bi34Te51 and Mn15Bi34Te51 alloys prepared by MA showed that the LaisBi34Te51 and Mn15Bi34Te51 alloys were synthesized with vacuum milling for 100 and 150 hours, and the nanostructured La15Bi34tTe51 compounds were synthesized after milling for 150 hours. It was found by The XRD analyses that the lanthanum atoms have intercalated into the layer structure of BizTea host by 150 hours and 370癈 annealing of the La15Bi34Te51 alloy. The Seebeck coefficient of La15Bi34Te51 suggests that the carrier scattering mechanism must be changed when the grain sizes decreased to a few nanometers, which lead to the Seebeck coefficient increases dramatically.The experimental results on the Bi0.5Sb1.5Te3/Polyaniline composites prepared by mechanical blending showed that the polymer additives do not lead to any remarkable decrease on the Seebeck coefficients of the composites, which applies that the scattering of carries in the composites must be significantly enhanced due to the dispersed polymer powders, and so that the Seebeck coefficient of the composites remain comparable withthe Bio.sSbi.sTea alloy, although the polymer has a much small Seebeck coefficient than the Bio.sSbi.sTea alloy. However the electrical conductivity of the composites decreases dramatically, which leads to a remarkable descent on their power factors.It was found that the composites prepared by in-situ polymerization have a remarkable higher electrical conductivity and so that a higher power factor than those of the composites prepared by mechanical blending, which suggests that the method of the in-situ polymerization could be helpful to decreasing the resistance of the polymer/alloy interfaces.