Effects of annealing on electrical properties of n-type Bi₂Te₃ fabricated by mechanical alloying and spark plasma sintering

N-type Bi₂Te₃ thermoelectric materials were firstly prepared by spark plasma sintering (SPS) using mechanically alloyed powders and then annealed at 423-593 K for 10-144 h. The samples were characterized by X-ray diffraction, scanning electron and optical microscope, and the Hall coefficient, electrical resistivity and Seebeck coefficient were measured. The effects of annealing conditions on the electrical transport properties were studied on the basis of the effective-medium-theory (EMT) and antisite defect model. The electrical transport properties of Bi₂Te₃ were reduced by annealing at 523 K and 593 K, but were improved by annealing at 423 K from 10 h to 144 h. The good property stability of the SPSed Bi₂Te₃ annealed at 423 K is attributed to the fact that lattice defects are reduced by appropriate annealing treatments.