Effect of Mechanical Deformation on Thermoelectric Properties of p-Type (Bi0.225Sb0.775)2Te3 Alloys

The effect of mechanical deformation and annealing on thermoelectric properties of p-type ( Bi0.225Sb0.775)Te-3 was performed. The ingots were prepared by melting, followed by quenching method using source materials with compositions of (Bi0.225Sb0.775)(2)Te-3. Rectangular shaped specimens (5 x 5 x 12 mm(3)) were cut from ingots and then cold-pressed at 700 MPa for 2 to 20 times by changing the press direction perpendicular to previous one. The cold-pressed samples have been annealed in a quartz ampoule at 573 K. The grain size of the samples was controlled by the number of cold-pressing process and annealing time. Fine grain structure with a grain size of not more than 10 mu m is obtained in highly deformed samples. The Seebeck coefficient of the deformed samples were gradually increased with annealing and converged to the similar value of about 225 mu V/K after 30 hrs. The small grain size in highly deformed sample enables a rapid increase of Seebeck coefficient with annealing time (similar to 2 hrs.), indicating that the thermal energy needed to recrystallize in highly deformed specimens is lower than that in low deformed specimens. Z values are rapidly increased with annealing time especially in highly deformed alloys, and converge to about 3.0 x 10(-3)/K at room temperature. A higher thermoelectric performance could be expected by the optimization of composition and microstructural adjustment. The present study experimentally demonstrates a simple and cost-effective method for fabricating Bi-Te-based alloys with higher thermoelectric performance.