Preparation of Thermoelectric Material Bi₂Te_2.85Se_0.15 by Mechanical Alloying-Hot Pressing and Melt Quenching Processes

Abstract

Bi₂Te_2.85Se_0.15 was prepared, without doping materials, by two different processes: mechanical alloying-hot pressing (MA-HP) and melt quenching (MQ). Doped Bi₂Te_2.85Se_0.15 is a well-known n-type Bi₂Te₃-based material. MA was carried out for 30 h. The MA-HP samples were obtained by hot pressing at 673 K under a mechanical pressure of 147 MPa in an argon atmosphere. The MQ samples were prepared by direct melting of the constituent elements at 973 K in an evacuated quartz ampoule followed by quenching into water.
These samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), optical microscopy (OM), and thermoelectric property measurements. The samples were identified as single-phase materials related to Bi₂(Te, Se)₃. The MA-HP sample showed n-type conduction, but the MQ sample showed p-type conduction. The carrier densities of the MA-HP and MQ samples at room temperature were, respectively, 1.80×10²⁵ m^-3 of n-type carriers and 2.90×10²⁵ m^-3 of p-type carriers. The maximum values of the figure of merit ZT for the MA-HP and the MQ samples were 0.853 at 313 K for n-type and 0.064 at 353 K for p-type, respectively.