Rational Synthesis of Ultrathin n-Type Bi₂Te₃ Nanowires with Enhanced Thermoelectric Properties

Abstract

A rational yet scalable solution phase method has been established, for the first time, to obtain n-type Bi(2)Te(3) ultrathin nanowires with an average diameter of 8 nm in high yield (up to 93%). Thermoelectric properties of bulk pellets fabricated by compressing the nanowire powder through spark plasma sintering have been investigated. Compared to the current commercial n-type Bi(2)Te(3)-based bulk materials, our nanowire devices exhibit an enhanced ZT of 0.96 peaked at 380 K due to a significant reduction of thermal conductivity derived from phonon scattering at the nanoscale interfaces in the bulk pellets, which corresponds to a 13% enhancement compared to that of the best n-type commercial Bi(2)Te(2.7)Se(0.3) single crystals (~0.85) and is comparable to the best reported result of n-type Bi(2)Te(2.7)Se(0.3) sample (ZT = 1.04) fabricated by the hot pressing of ball-milled powder. The uniformity and high yield of the nanowires provide a promising route to make significant contributions to the manufacture of nanotechnology-based thermoelectric power generation and solid-state cooling devices with superior performance in a reliable and a reproducible way.

Design Principle of Telluride-Based Nanowire Heterostructures for Potential Thermoelectric Applications

“…Second, the Seebeck coefficient in our Te−Bi 2 Te 3 nanowire heterostructures (608 μV·K −1 at 300 K and 588 μV·K −1 at 400 K) is also considerably higher than that of Te nanowires (408 μV·K −1 at 298 K), 29 Te bulk crystals (340 μV·K −1 at 293 K), and pure Bi 2 Te 3 nanowires reported previously by our group (205 μV·K −1 at 300 K and 245 μV·K −1 at 400 K). 21 The largely enhanced Seebeck coefficient could result from the energy filtering effect occurring at grain−grain interfaces, as seen in Figure 5A in our hot pressed samples. To decide whether there is any energy filtering effect happening in the heterostructure, the work function and band gap of tellurium and bismuth telluride need to be experimentally determined.…”

“…Using anhydrous hydrazine in the reaction will only lead to the formation of pure Bi 2 Te 3 nanowires with a much thinner diameter, which is consistent with our previous report. 21 Decreasing the amount of 80% hydrazine hydrate added into the reaction (Figure 3) leads to the growth of a thicker Te nanowire body with larger Bi 2 Te 3 plates and promotes multiple nucleation and growth of Bi 2 Te 3 plates along the surface of Te nanowires ( Figure 3D). Examining and understanding these observations suggest a possible growth mechanism for the "barbell" heterostructure: it has been widely accepted that the tips of nanowires usually possess the highest reactivity where the reaction/growth tends to happen first.…”

“…34,35 Third, the thermal conductivity of our sample (0.365 W·m −1 ·K −1 at 300 K and 0.309 W·m −1 ·K −1 at 400 K) is only ∼16% of bulk Te crystal (2.27 W·m −1 ·K −1 at 293 K) and ∼26% of pure Bi 2 Te 3 nanowires reported previously (1.42 W·m −1 ·K −1 at 300 K and 1.19 W·m −1 ·K −1 at 400 K). 21 Such a low thermal conductivity is comparable to the Te nanowire−poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) composite (0.22−0.30 W·m −1 ·K −1 at 298 K) and pure organic PEDOT:PSS polymer (0.24−0.29 W·m −1 ·K −1 at 298 K), 29 which directly benefits from the enhanced phonon scattering at nanowire−nanowire, nanowire−plate, and plate−plate interfaces. Lastly and most importantly, the ZT of our Te−Bi 2 Te 3 nanowire heterostructure-based composite is more than two orders better than pure Te nanowires (0.0004 at 298 K) and 2.4 times better than the Te nanowire−PEDOT:PSS composite (0.1 at 298 K).…”

Composition Modulation of Ag2Te Nanowires for Tunable Electrical and Thermal Properties

“…To remove the surface ligands, the Ag 2 Te nanowires are dispersed in 800 ml ethanol and mixed with 80 ml N 2 H 4 •H 2 O under vigorous stirring for a day. [1][2][3] The nanowires are then collected with centrifugation and washed with DI water for three times.…”

A novel route to nanostructured bismuth telluride films by electrodeposition

“…Zhang and co-workers [12] have reported a non-templated solvo-thermal route to ultrathin Bi 2 Te 3 nanowires with average diameters of 80 Å. This requires temperatures of 160 °C to produce the separate nanowires; they are then spark plasma sintered at several hundred °C and 50 MPa axial pressure to consolidate the wires into a continuous electrical contact.…”