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Synthesis and Thermoelectric Properties of RXTe3(X=Bi,Sb) Compound at Low Temperatures

Author: YangErHao
Tutor: HuoDeZuo
School: Hangzhou University of Electronic Science and Technology
Course: Physical Electronics
Keywords: thermoelectric material Bi-Te alloy mechanical alloying solid phase reaction high energy ball milling grain refinement n-type doping
CLC: TB34
Type: Master's thesis
Year: 2014
Downloads: 1
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Abstract


With a gradually serious problem of energy shortages and global environmental pollution,exploiting new and clean energy sources is becoming more and more important to cover the futuredemands. Thermoelectric(TE) materials is a new semiconductor functional materials, which candirectly convert heat energy into electricity or vice versa. TE devices based on the Seebeck effectand Peltier effect has been widely used in many fields, such as aerospace, medicine andmicroelectronics. The devices with the advantages of non-pollution, non-noise, safe and reliable andetc, has become an important and promising way to convert heat energy to electricity. Bi2Te3, andits alloys which is the widest application in the business are the best TE materials available todaynear room temperature with the highest dimensionless figure of merit ZT of about1.Much effort has been made to try to improve the thermoelectric properties of Bi-Te basedalloys, including metal doping and alloying. It has been found that alloying and the addition ofsmall amounts of metal can effectively improve the TE transport properties and raise the figure ofmerit. In order to further improve the TE efficiency of Bi2Te3based alloy, hence, in this study, thecomposition, crystal structure, technological parameter of the Bi2Te3, Sb2Te3based alloys areinvestigated. Rare earth (RE) elements were used as dopants to improve the TE transport properties.The main results are listed as follows:1. PrBiTe3, GdBiTe3,GdSbTe3ternary alloy compounds were successfully produced by solidstate reaction and mechanical alloying technique with control the ball milling time. The theoreticalresearch shows that there are comparatively strong interaction between the electrons of the alloysdoped by RE elements, which causes a relatively large effective mass. which is called “heavyfermion semiconductor materials”, which can increase the Seebeck coefficient of Bi-Te based alloyand improve the TE transport properties. The experiment result shows that, at room temperature, theSeebeck coefficient of the GdSbTe3can reach365μV/K.2. The technology of high-energy ball milling in the study can effectively decrease the grainsize and introduce lots of crystal boundary inner the alloys which can depress the phonon thermalconductivity. Simultaneously, the introducing of quantum effect contributes to improving thethermoelectric transport properties. The analysis of the experiment result indicates that theminimum contribution of the crystal lattice vibration to the thermal conductivity is just0.8Wm-1K-1at room temperature. 3. For the Bi-Te based alloys, the proper doping of rare earth can effectively better the carrierconcentration. The existing theoretical calculations suggest that, the optimum carrier concentrationwhich can make the materials show the best properties is in the range of1019~1020cm-3. Accordingto the measurement result, the carrier concentration of GdBiTe3, PrBiTe3respectively are2.3×1019cm-3,1.5×1019cm-3at room temperature, Corresponding the hall coefficient are2.8×10-7m3/C,2.5×10-7m3/C.4. The ternary alloy compounds RXTe3show the phenomenon of the magnetoresistance effectto varying degrees, when the magnetic field changes from0to9T, the change of the resistivity canreach the maximum value0.03m, accounting for3.75%of the resistivity of the materials.5. The result shows that, the figure of merit of the Bi-Te based ternary rare earth alloy is onlyabout0.01. There is a relatively large distance compared with some advanced Bi2Te3basedmaterials at present. The replacement of Bi atom to Pr atom or Gd atom has no obvious effect to theTE transport properties, but the n-type doping inner the material. The increase of the effective mass,grain refinement, the optimization of the component does not improve the power factor of the alloysignificantly and we should further optimize the carrier concentrate and increase the properties ofthe materials. In addition, the theory about how the rare earth effect the TE transport properties ofthe special alloys should be studied further.

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