Fine‐Grained and Nanostructured AgPb_mSbTe_m+2 Alloys with High Thermoelectric Figure of Merit at Medium Temperature

Abstract

. IntroductionThermoelectric (TE) materials have drawn increasing attention because of their potential applications in energy harvesting and electronic cooling devices. [ 1,2 ] The performance of a thermoelectric material is defi ned by its dimensionless fi gure of merit ZT = α 2 ( ρ κ ) −1 T , where α is the Seebeck coeffi cient (also called as thermopower), T is the absolute temperature, ρ is the electrical resistivity, and κ is the thermal conductivity. [ 3 ] Extensive research has been carried out attempting to discover thermoelectric materials with higher performance. [4][5][6][7][8][9][10] Among different types of TE materials, lead telluride (PbTe) has demonstrated a relatively high ZT value in the medium temperature region, which makes it a suitable material for power generation rather than cooling applications. [ 11 ] Many studies have been focused on the doping of PbTe alloys to optimize its carrier concentration, [ 12,13 ] manipulate its electronic density of states, [ 14 ] microstructure [ 15 ] as well as endotaxial nanostructure. [16][17][18] In 2004, Hsu et al. fi rst reported high ZT values of PbTe-based AgPb m SbTe m +2 alloys, which were abbreviated as LAST alloys by taking the names of constitutive elements. [ 19 ] The main contribution to the high ZT value in LAST alloys is their nanostructure feature with nanoscopic precipitates or nanodots with compositional fl uctuation, which reduces thermal conductivity due to enhanced phonon scattering but not greatly affects electrical conduction, owing to the endotaxial interface between the precipitates and the matrix. [ 19 ] In fact, our previous study revealed that thermal conductivity and electrical resistivity can be reduced at the same time by a traditional annealing treatment that facilitated the in-situ formation of precipitates of 5-20 nm in diameter. [ 20 ] A recent study has shown that optimization of hierarchical architecture from mesoscale grains and grain boundaries to nanoscale endotaxial precipitates is effective for further ZT enhancement. [ 21 ] This work recalled the importance of controlling grain-level microstructure, which can be easily realized in most thermoelectric materials. It is well known that refi ning microstructure by reducing grain sizes is a general approach to lowering the thermal conductivity. In fact, great ZT enhancement has been achieved in several kinds of thermoelectric alloys, and among them a good example is that signifi cant ZT elevation can be realized in half-Heusler alloys that have high thermal conductivity, which can be signifi cantly lowered by reducing grain sizes [ 22 ] or via a nanocomposite approach. [ 23 ] It was reported that grain refi nement could also lead to an increase in Seebeck coeffi cient in some thermoelectric materials due to an enhanced energy fi ltering effect at grain boundaries. [ 15,24 ] With a motivation to further increase the thermoelectric performance, a repeated mechanical alloying (MA)-spark plasma sintering (SPS) method was applied to the fabrication of LAST alloys and was in...

High-performance thermoelectric Cu2Se nanoplates through nanostructure engineering

“…This value has achieved over 20% improvement when compared with reported bulk Cu 2 Se [13]. In fact, this value is comparable to those highest thermoelectric materials reported so far [2,4,29,30]. To fundamentally understand our observed exceptional thermoelectric performance, detailed structural characterizations were performed on the sintered pellets.…”

PbTe-based thermoelectric nanocomposites with reduced thermal conductivity by SiC nanodispersion

“…9,26,27 Second, the incorporation of SiC nanoparticles refined the grains, leading to enhanced grain boundary scattering effect to reduce the lattice thermal conductivity in this polycrystalline LAST alloy. Such an effect was also realized in our previous work, 18 in which the microstructure was refined in a different way. Third, but importantly, the SiC nanodispersion effect of reducing lattice thermal conductivity of the present nanocomposites should be enhanced at the interfaces between the nanodispersions and the matrix by the existence of mismatched layer or spacing, as shown below.…”

“…16 Especially, in PbTe-based AgPb m SbTe mþ2 (LAST, lead-antimony-silver-tellurium) compounds, a high ZT value up to 1.7 at 700 K was achieved by Hsu et al in 2004. 17 Previous studies 9,17,18 indicated that the endotaxial nanostructure is very effective in enhancing ZT value of LAST alloys, such as the phase-segregation with the presence of embedded nanodots (appear to be rich in Ag and Sb) in the PbTe matrix, which are believed to play an important role in scattering phonons without influencing electron transport meanwhile. However, one may worry about the stability of such a nanostructure when used for a long time at high temperatures.…”

Enhanced thermoelectric performance of In2O3-based ceramics via Nanostructuring and Point Defect Engineering

“…However, the ZT value of n -type TE oxides (e.g., SrTiO 3 11, ZnO12, CaMnO 3 13) is still lower in terms of assembling a practical oxide-based TE device due to its mediocre electrical conductivity σ (~100–200 S.cm −1 ) and/or high thermal conductivity κ = ( κ l + κ e ) (~2–10 W.m −1 .K −1 ). In this regard, two main strategies have recently been applied to improve the ZT : One is to enhance the power factor ( S 2 σ ) by tuning the carrier concentration14, or band engineering151617 and the other is to reduce κ L by enhancing phonon scattering through solid solutions and nanostructuring2318. In fact, our previous work reveals that thermal conductivity can be reduced from 3 W m −1 K −1 (micron sample) to 2.2 W m −1 K −1 (nanostructured sample) in In 2 O 3 -based ceramics19.…”