Preparation And The Thermoelectric Properties Of The Bi₂Te₃ Based Thermoelectric Materials

Bi2Te3 compounds and their solid solutions, with the high figures of merit about 1, have received considerable attention due to their great potential for applications in refrigeration. In this work, Bi2Te3-based alloys were prepared with vacuum melting, pressureless sintering and mechanical alloying. Special consideration has been taken on the alloying with the rare earth elements, since many rare earth contained compounds have an unusual electronic state called the intermediate valence state, which leads to a high Seebeck coefficient. In the present work, the microstuctures and transport properties of E^Tea-based alloys were investigated by means of XRD analysis, SEM/EDS observations and the measurements of XPS.It was found that LaBi^ee and SmBi^eg alloys could be synthesized successfully only by the method of mechanical alloying with rotation speed of 220rpm, instead of the method of vacuum melting, pressureless sintering and mechanical alloying with lower rotation speed (150 rpm).It was shown that the addition of the rare earth elements facilitates the formation of nanostructured LaBi/tTee and SmBi/tTeg alloys. The grain sizes of LaBi4Te6 and SmBi4Tee alloys were 9.40nm and 11.06nm before hot pressing, respectively, and increased to 22.13nm and 25.27nm after hot pressing.Compared with Mni5Bi34Te5i, the experimental results revealed that the LaBi4Tes and SmBi4Te6 have higher Seebeck coefficients and power factors in the 350-500K temperature range. On the one side this is because of the special energy band structure of the rare earth compound. On the other side, when the grain sizes decreased to a few nanometers, the carrier scattering mechanism was changed. At the same temperature, Seebeck coefficient of SmBi4Te6 is about 10u.VK~' higher than that of LaBi4Te6, due to the 4f orbital in samarium atoms.