Preparation and thermoelectric properties of iodine-doped Bi2Te3-Bi2Se3 solid solutions

Abstract

Bismuth chalcogenides, such as p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3, are known to have excellent thermoelectric properties at temperatures near room temperature. Since Bi2Te3, Sb2Te3 and Bi2Se3 have the same class of crystal symmetry, they can form homogeneous solid solutions. The thermoelectric figure of merit can be improved by increasing the power factor through doping to optimize the carrier concentration and/or by reducing the thermal conductivity through the formation of solid solutions for phonon scattering. In this study, n-type Bi2Te2.7Se0.3:Im (m = 0.0 -0.015) solid solutions were successfully prepared by using encapsulated melting and hot pressing. The increase in the carrier concentration induced by I doping led to an increase in both the electrical conductivity and the electronic thermal conductivity, with I atoms acting as phonon scattering centers reducing the lattice thermal conductivity. The undoped solid solution had a carrier concentration of 6.27 × 10 19 cm −3 , a power factor (PF ) of 1.71 mWm −1 K −2 , and a dimensionless figure of merit (ZT ) of 0.54 at 323 K. However, the ZT value was improved by I doping due to the increased PF, demonstrating a maximum of ZT = 1.13 at 423 K for Bi2Te2.7Se0.3:I0.0075.

Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi2Te2.85Se0.15Ix Compounds

“…[ 3 ] The p-type bismuth tellurides show high zT values in the hot-deformed Bi 0.3 Sb 1.7 Te 3 (1.3 at 380 K) [ 4 ], Te-excess Bi 0.4 Sb 1.6 Te 3 (1.41 at 147 K) [ 5 ], melt-spun BiSbTe alloys (1.24 at 350 K [ 6 ] and 1.56 at 300 K [ 7 ]). The n-type bismuth tellurides also show relatively high zT values such as hot-deformed Bi 2 Te 2.3 Se 0.7 (1.2 at 445 K) [ 4 ], Cu-doped polycrystalline Bi 2 Te 2.7 Se 0.3 (1.10 at 373 K) [ 8 ], I-doped polycrystalline Bi 2 Te 2.7 Se 0.3 (1.13 at 423 K) [ 9 ], CuI-doped Bi 2 Te 2.7 Se 0.3 with hot-deformation (1.07 at 423 K) [ 10 ], textured Bi 2 Te 2.7 Se 0.3 nano crystal (1.31 at 438 K) [ 11 ], Se-deficiency polycrystalline Bi 2 Te 2.3 Se 0.69 (1.2 at 450 K) [ 12 ] and hot-deformed Bi 1.95 Sb 0.05 Te 2.3 Se 0.7 ( zT = 1.3 at 450 K) [ 13 ].…”

“…Even though the thermoelectric performance of n-type bismuth tellurides has been progressing significantly, the zT values of the n-type materials are not compatible with those of the p-type properties because the thermoelectric device’s performance is mainly determined by the average zT values of p-and n-type materials. [ 14 ] To reach high thermoelectric performance in n-type bismuth tellurides, there have been many studies such as the control of Se concentration Bi 2 Te 3−x Se x [ 4 , 11 , 15 , 16 ], Cu-doping [ 8 , 17 ], I-doping [ 9 , 17 ] Ga-doping [ 18 ], CuI-doping [ 10 , 19 , 20 ], hot-press and hot-deformation processes [ 8 , 13 , 21 , 22 , 23 , 24 ], etc.…”

“…Iodine is a good n-type dopant of the bismuth tellurides, which can tune the Fermi level. It is also known that iodine doping reduces lattice thermal conductivity but the origin is not fully understood yet [ 9 , 17 , 25 , 26 ]. Recently, we found that the lattice distortion (or charge density wave formation) by the CuI-doping can decrease the lattice thermal conductivity with the enhancement of Hall carrier mobility [ 20 , 27 ].…”

Thermoelectric degrees of freedom determining thermoelectric efficiency

“…The dataset consists of Seebeck coefficient a, electrical resistivity r, and thermal conductivity k at measured temperature T. For the numerical computation of efficiency, we use the available temperature ranges of the given material: the T c is defined as the maximum of the lowest measured temperautre and T h is defined as the minimum of the highest measured temperature for given materials. Heremans et al (2008); Hsu et al (2004);Hu et al (2014Hu et al ( , 2016; Kim et al (2015c); Lin et al (2016); Liu et al (2011Liu et al ( , 2012b; Pan and Li (2016); Pei et al (2011g, 2011c; Poudel et al (2008); Rhyee et al (2009); Wang et al (2014a); Zhao et al (2012aZhao et al ( , 2012bZhao et al ( , 2014Zhao et al ( , 2015; Cui et al (2007Cui et al ( , 2008; Eum et al (2015); Fan et al (2010); Han et al (2013); Hsu et al, 2014;Zheng et al (2014);Hu et al (2015); Hwang et al (2013); Ko et al (2013); Zhang et al (2015b); Zhao et al (2005); Lee et al (2010Lee et al ( , 2013cLee et al ( , 2013a; Yan et al (2010); Lee et al (2013bLee et al ( , 2014cLee et al ( , 2014bLee et al ( , 2014aLee et al ( , 2014d (2011a, 2011e, 2011f, 2011d, 2012a, 2012b, 2014);…”

Influence of Ga-doping on the thermoelectric properties of Bi(2−x)GaxTe2.7Se0.3 alloy

“…Lee et al [13] reported that the increase in the carrier concentration induced by I doping led to an increase in the electrical conductivity. The ZT value was improved by I doping due to the increased PF, demonstrating a maximum of ZT ¼ 1.13 at 423 K for Bi 2 Te 2.7 Se 0.3 :I 0.0075 .…”