Synthesis and thermoelectric properties of bismuth antimony telluride thermoelectric materials fabricated at various ball-milling speeds with yttria-stabilized zirconia ceramic vessel and balls

Abstract

p-type Bi0.3Sb1.7Te3.0 thermoelectric materials were fabricated at various ball-milling speeds with yttria-stabilized zirconia (YSZ) ceramic balls in an YSZ vessel, and then hot-pressed. The powders milled at speeds of or higher than 150 rpm were completely alloyed and single-phase Bi0.3Sb1.7Te3.0 was obtained. The grain size of a disk sintered at 350 °C was approximately 1 μm at a fracture surface. The Seebeck coefficients of sintered disks fabricated by YSZ milling were higher while their electrical conductivities were lower than those of disks fabricated by using a stainless-steel vessel and Si3N4 balls, as the YSZ milling suppressed the contamination by materials acting as carrier dopants in the Bi0.3Sb1.7Te3.0 bulk. The contamination from the YSZ vessel and milling balls did not affect the phonon thermal conductivities of the Bi0.3Sb1.7Te3.0 bulk materials. The dimensionless figure of merit ZT of the sample milled at 150 rpm with the YSZ vessel and balls and sintered at 350 °C was approximately 1.7 times that of the sample milled with the stainless-steel vessel and Si3N4 balls. ZT remained above 1.0 and reached the peak of 1.16 (α: 295 μV/K, σ: 4.16 ×104 S/m, κ: 0.94 W/(m K)) at room temperature for the sample milled at 130 rpm and hot-pressed at 350 °C. Thus, the thermoelectric properties can be improved by selecting appropriate milling vessels and balls.