The Preparation And Properties Of Bi₂Te₃ Based Thermoelectric Alloys

This paper have reviewed detailed the thermoelectricity, the history of thermoelectric materials. The studies in existence showed that the solid solutions which based with Bi₂Te₃ and doped with other elements are the best thermoelectric semiconductors working at low-temperature at present.The n-type Bi₂(Te_0.0975Se_0.025)₃ and p-type (Bi_0.2Sb_0.8)₂Te₃ thermoelectric semiconductor alloys were prepared by powder metallurgy method and spark plasma sintering. The relationship between thermoelectric properties of samples and sinter temperature were researched, and the best preparation craftwork were been ensured. The result showed that because of Bi and Se elements have low melting point and boil point, it is easily gasification and separation in the process of melting and sinter which influenced the thermoelectric properties of samples. Ar gas was filled when melting the alloys and used lower sinter temperature. Higher sinter temperature is in favor of the electrical conductivity go against Seebeck coefficient to p-type materials. When the sinter temperature is increasing, the electrical conductivity decreased and increased, the Seebeck coefficient increased and decreased to n-type materials. The melting temperature of n-type Bi₂Te₃ based thermoelectric material is 620℃, the best sinter temperature is 400 ℃ and they are 700℃ and 470℃ for p-type.The element compound of n-type Bi₂(Te_1-xSe_x)₃ and p-type (Bi_1-xSb_x)₂Te₃ solid solutions were researched. The solid solutions with different x were prepared and their thermoelectric properties were compared. The result showed that the best n-type alloys and p-type alloys can be got when x=0.1⁰.15 and x=0.7⁰.8, the ZT are about 0.8 and 1.16.The samples in perpendicular and parallel sections to the pressing direction were studied. The XRD analysis indicate that the X-ray diffraction apex of crystal surfaces occur obvious difference in different direction. The SEM micrographs show that the appearance of samples are different in different directions. This argued that alloys are anisotropic. When the sinter temperature increasing the crystal orientation of p-type is increasing too, but the crystal orientation of n-type has not obvious change.