title: Experimental studies on anisotropic thermoelectric properties and structures of n-type Bi2Te2.7Se0.3.
abstract: The peak dimensionless thermoelectric figure-of-merit (ZT) of Bi(2)Te(3)-based n-type single crystals is about 0.85 in the ab plane at room temperature, which has not been improved over the last 50 years due to the high thermal conductivity of 1.65 W m(-1) K(-1) even though the power factor is 47 x 10(-4) W m(-1) K(-2). In samples with random grain orientations, we found that the thermal conductivity can be decreased by making grain size smaller through ball milling and hot pressing, but the power factor decreased with a similar percentage, resulting in no gain in ZT. Reorienting the ab planes of the small crystals by repressing the as-pressed samples enhanced the peak ZT from 0.85 to 1.04 at about 125 degrees C, a 22% improvement, mainly due to the more increase on power factor than on thermal conductivity. Further improvement is expected when the ab plane of most of the small crystals is reoriented to the direction perpendicular to the press direction and grains are made even smaller.
authors.affiliation: Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA.
authors.forename: Xiao
authors.initials: X
authors.lastname: Yan
authors.forename: Bed
authors.initials: B
authors.lastname: Poudel
authors.forename: Yi
authors.initials: Y
authors.lastname: Ma
authors.forename: W S
authors.initials: WS
authors.lastname: Liu
authors.forename: G
authors.initials: G
authors.lastname: Joshi
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Lan
authors.forename: Dezhi
authors.initials: D
authors.lastname: Wang
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.forename: Z F
authors.initials: ZF
authors.lastname: Ren