Simple evaluation of the maximum thermoelectric figure of merit, with application to mixed crystals SnS1-xSex

Wasscher, J.D.; Albers, W.; Haas, C.

doi:10.1016/0038-1101(63)90083-2

Cited by 49 publications

(44 citation statements)

References 6 publications

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“…Intriguingly, our results for the remaining two axes disagree markedly with Ref. 5 8 The origin of this bc anisotropy can be traced to the phonon dispersions in Fig. 2: the average phonon frequencies and group velocities are higher along Γ → Y than along Γ → Z.…”

contrasting

confidence: 80%

Low thermal conductivity and triaxial phononic anisotropy of SnSe

Carrete

Mingo

Curtarolo

2014

Applied Physics Letters

242

201

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In this theoretical study, we investigate the origins of the very low thermal conductivity of tin selenide (SnSe) using ab-initio calculations. We obtained high-temperature lattice thermal conductivity values that are close to those of amorphous compounds. We also found a strong anisotropy between the three crystallographic axes: one of the in-plane directions conducts heat much more easily than the other. Our results are compatible with most of the experimental literature on SnSe, and differ markedly from the more isotropic values reported by a recent study.The ongoing quest for improved thermoelectric materials has spanned the past six decades. 1,2 Good thermoelectrics are characterized by their high figures of merit ZT = P T /κ. This requires a low thermal conductivity κ, and a high power factor P = σS 2 (where σ is the electrical conductivity, and S the thermopower) across their intended range of working temperatures. Nanotechnology has been able to greatly improve on earlier single-crystal thermoelectric materials 3 via hindering phonon flow while keeping favorable electric properties, even when starting from a poor performer such as bulk silicon. 4 Thus, it was somewhat surprising when single-crystal SnSe recently emerged as the best thermoelectric material ever measured. Experimental measurements on monocrystalline samples 5 point to a record figure of merit of ZT = 2.6 at T = 923 K. This is due mainly to its very low lattice thermal conductivity κ . Intense interest in SnSe was spurred by these results, and to date two independent sets of measurements on polycrystals have been published. 6,7 The two series are compatible with each other, yet they both display higher values of κ than those reported in Ref. 5 for the single crystal. This contrasts with the expectation that grain boundaries should decrease the thermal conductivity below that of the single crystal. Remarkably, preexisting studies of single crystals 8 reported even higher values of κ, with a directional maximum of around 1.8 W m −1 K −1 at room temperature.To address this controversy, we studied phonon transport in SnSe from first principles based on the Boltzmann transport equation (BTE) formalism. Such modeling studies offer substantially more detailed information than is readily available from the experiments, and have demonstrated both their wide range of applicability and their predictive power. 9-13 For the present work, we focused on the Pnma-symmetric phase of SnSe. This is the stable phase from room temperature up to ∼ 750 − 800 K. 5 Hence, it is the pertinent phase for most of the aforementioned measurements. We started with an atomistic description of Pnma SnSe extracted from the AFLOWLIB.org consortium repository [auid=aflow:d188eb9b8df60e58]. 14,15 We relaxed the structure without any geometrical constraint using the density functional theory (DFT) software package VASP. 16 All technical details are presented in the supplementary material. We obtained unit cell lengths of a = 11.72Å, b = 4.20Å and c = 4.55Å, which are in reasonab...

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contrasting

confidence: 80%

Low thermal conductivity and triaxial phononic anisotropy of SnSe

Carrete

Mingo

Curtarolo

2014

Applied Physics Letters

242

201

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“…Although their optical properties have been intensively investigated 22,23 , their thermoelectric properties have long been ignored since a simple study in 1963, which reported room temperature ZTs of 0.15 for SnSe and 0.27 for SnS, respectively 24 . Recently, ZTs as high as…”

Section: Introductionmentioning

confidence: 99%

First-principles study of anisotropic thermoelectric transport properties of IV-VI semiconductor compounds SnSe and SnS

Guo¹,

Wang²,

Kuang³

et al. 2015

Phys. Rev. B

428

406

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Tin selenide (SnSe) and tin sulfide (SnS) have recently attracted particular interest due to their great potential for large-scale thermoelectric applications. A complete prediction of the thermoelectric performance and the understanding of underlying heat and charge transport details are the key to further improvement of their thermoelectric efficiency. We conduct comprehensive investigations of both thermal and electrical transport properties of SnSe and SnS using first-principles calculations combined with the Boltzmann transport theory. Due to the distinct layered lattice structure, SnSe and SnS exhibit similarly anisotropic thermal and electrical behaviors. The cross-plane lattice thermal conductivity  L is 40-60% lower than the in-2 plane values. Extremely low  L is found for both materials because of high anharmonicity while the average  L of SnS is ~ 8% higher than that of SnSe from 300 to 750 K. It is suggested that nanostructuring would be difficult to further decrease  L because of the short mean free paths of dominant phonon modes (1-30 nm at 300 K) while alloying would be efficient in reducing  L considering that the relative  L contribution (~ 65%) of optical phonons is remarkably large. On the electrical side, the anisotropic electrical conductivities are mainly due to the different effective masses of holes and electrons along the a, b and c axes. This leads to the highest optimal ZT values along the b axis and lowest ones along the a axis in both p-type materials.However, the n-type ones exhibit the highest ZTs along the a axis due to the enhancement of power factor when the chemical potential gradually approaches the secondary conduction band valley that causes significant increase in electron mobility and density of states. Owing to the larger mobility and smaller  L along the given direction, SnSe exhibits larger optimal ZTs compared with SnS in both p-and n-type materials. For both materials, the peak ZTs of n-type materials are much higher than those of p-type ones along the same direction. The predicted highest ZT values at 750 K are 1.0 in SnSe and 0.6 in SnS along the b axis for the p-type doping while those for the n-type doping reach 2.7 in SnSe and 1.5 in SnS along the a axis, rendering them among the best bulk thermoelectric materials for large-scale applications. Our calculations show reasonable agreements with the experimental results and quantitatively predict the great potential in further enhancing the thermoelectric performance of SnSe and SnS, especially for the n-type materials.

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“…23 This material was scarcely studied as TE materials due to the large band gap ~0.9 eV. [35][36][37][38][39] The high ZT is solely attributed to the intrinsically ultralow thermal conductivity due to high anharmonicity of the chemical bonds. 23,40,41 Considering the large-scale applications and the poor mechanical properties in the layered single crystal SnSe (crystallized in the orthorhombic Pnma space group), SnSe polycrystals were then studied.…”

Section: Introductionmentioning

confidence: 99%

“…27 SnS (crystallized in the orthorhombic Pbmn space group) has the similar layered structure with SnSe and even larger band gap ~1.21 eV. 35,36,38,39,42,43 Potential application of this environmentally compatible and low-cost material was predicted by first principles calculation 44 and a ZT of ~0.6 at about 900 K was recently obtained in p-type Ag-doped SnS polycrystals. 29 However, there is no report on ntype tin chalcogenide alloys up to now.…”

Section: Introductionmentioning

confidence: 99%

Studies on Thermoelectric Properties of n‐type Polycrystalline SnSe_1‐xS_x by Iodine Doping

Zhang

Chere

Sun

et al. 2015

Advanced Energy Materials

301

240

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We prepared iodine-doped n-type SnSe polycrystalline by melting and hot pressing. The prepared material is anisotropic with a peak ZT of ~0.8 at about 773 K measured along the hot pressing direction. This is the first report on TE properties of n-type Sn chalcogenide alloys.With increasing content of iodine, the carrier concentration changed from 2.3×10 17 cm -3 (p-type)to 5.0×10 15 cm -3 (n-type) then to 2.0×10 17 cm -3 (n-type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p-type SnSe. By alloying with 10 atm. % SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ~1.0 at about 773 K measured also along the hot pressing direction.

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Simple evaluation of the maximum thermoelectric figure of merit, with application to mixed crystals SnS1-xSex

Cited by 49 publications

References 6 publications

Low thermal conductivity and triaxial phononic anisotropy of SnSe

Low thermal conductivity and triaxial phononic anisotropy of SnSe

First-principles study of anisotropic thermoelectric transport properties of IV-VI semiconductor compounds SnSe and SnS

Studies on Thermoelectric Properties of n‐type Polycrystalline SnSe_1‐xS_x by Iodine Doping

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Simple evaluation of the maximum thermoelectric figure of merit, with application to mixed crystals SnS1-xSex

Cited by 49 publications

References 6 publications

Low thermal conductivity and triaxial phononic anisotropy of SnSe

Low thermal conductivity and triaxial phononic anisotropy of SnSe

First-principles study of anisotropic thermoelectric transport properties of IV-VI semiconductor compounds SnSe and SnS

Studies on Thermoelectric Properties of n‐type Polycrystalline SnSe1‐xSx by Iodine Doping

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Studies on Thermoelectric Properties of n‐type Polycrystalline SnSe_1‐xS_x by Iodine Doping