Thermoelectric Properties Of SnSe Research Articles

Microstructural Instability and Its Effects on Thermoelectric Properties of SnSe and Na-Doped SnSe.

Effects of thermal cycling on the microstructure and thermoelectric properties are studied for the undoped and Na-doped SnSe samples using X-ray computed tomography and property measurements. It is observed that thermal cycling causes significant cracks to develop, which decrease both the electrical and lattice thermal conductivities but do not affect the thermopower. The zT values are drastically reduced after the repeated heat treatment. It is important to account for density changes during cycling to obtain accurate values of the thermal conductivity. Even before thermal cycling, the spark-plasma sintered (SPS) samples have a significant number of microcracks. The orientation of cracks within the SPS pellets and their effect on the microstructure are influenced by the presence of a Na-rich impurity. The SnSe and Sn0.995Na0.005Se samples without the impurity develop cracks and exhibit grain growth parallel to the pellet surface, which is also the plane of the 2D SnSe layers. The Sn0.97Na0.03Se sample containing the impurity develops cracks that are orthogonal to the pellet surface. Such an orientation of cracks in Sn0.97Na0.03Se inhibits grain growth. All samples appear mechanically unstable after thermal cycling.

Ultrahigh power factor of Bi/Zn co-doped SnSe: Mechanical and thermoelectric properties on DFT level

Tin selenide-based materials have attracted much attention recently because of their unique properties. This study employs first-principles calculations and density functional theory (DFT) to investigate the impact of Bismuth and Zinc co-doping on the electronic, mechanical, and thermoelectric properties of SnSe. The co-doped system exhibits a triclinic crystal structure and shows enhanced electrical conductivity and the generation of n-type carriers. The co-doped SnSe also demonstrates improved mechanical stability, higher susceptibility to shear deformation, and increased deformability under shear stresses. Thermoelectric calculations reveal significantly enhanced power factor (PF) values compared to pristine SnSe and single-doped Zn and Bi SnSe structures, with a maximum PF of 63.0 μV/Kcm at 800 K. These findings highlight the potential of Bi and Zn co-doped SnSe as a promising high-performance thermoelectric material and provide valuable insights for further research in SnSe-based materials.

Enhancement of the Seebeck Coefficient of C doped SnSe: First Principles Study

The effect of C dopant on the electronic structure and thermoelectric properties of SnSe has been studied using density functional theory (DFT) and by solving the Boltzmann transport equation (BTE). We found that the substitution of C into the Sn site creates a strongly localized defect state with a sharp density for the state peak. This strong modification of band structure reduces the band gap from 0.61 eV to 0.42 eV. It was found that the maximal Seebeck coefficient can be enhanced up to 17.1% and the maximal temperature reduces from 525 K to 280 K. These behaviors can be understood using the Mott equation and Goldsmid – Sharp relation.

High-Performance Thermoelectrics Based on Solution-Grown SnSe Nanostructures.

Two-dimensional layered tin selenide (SnSe) has attracted immense interest in thermoelectrics due to its ultralow lattice thermal conductivity and high thermoelectric performance. To date, the majority of thermoelectric studies of SnSe have been based on single crystals. However, because synthesizing SnSe single crystals is an expensive, time-consuming process that requires high temperatures and because SnSe single crystals have relatively weaker mechanical stability, they are not favorable for scaling up synthesis, commercialization, or practical applications. As a result, research on nanocrystalline SnSe that can be produced in large quantities by simple and low-temperature solution-phase synthesis is needed. In this Perspective, we discuss the progress in thermoelectric properties of SnSe with a particular emphasis on nanocrystalline SnSe, which is grown in solution. We first describe the state-of-the-art high-performance single crystal and polycrystals of SnSe and their importance and drawbacks and discuss how nanocrystalline SnSe can solve some of these challenges. We illustrate different solution-phase synthesis procedures to produce various SnSe nanostructures and discuss their thermoelectric properties. We also highlight a unique solution-phase synthesis technique to prepare CdSe-coated SnSe nanocomposites and its unprecedented thermoelectric figure of merit (ZT) of 2.2 at 786 K, as reported in this issue of ACS Nano. In general, solution synthesis showed excellent control over nanoscale grain growth, and nanocrystalline SnSe shows ultralow thermal conductivity due to strong phonon scattering by the nanoscale grain boundaries. Finally, we offer insight into the opportunities and challenges associated with nanocrystalline SnSe synthesized by the solution route and its future in thermoelectric energy conversion.

Realizing high thermoelectric performance in hot-pressed polycrystalline AlxSn1-xSe through band engineering tuning

SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit. We synthesized polycrystalline AlxSn1-xSe (x = 0.01, 0.02, 0.03 and 0.04) by hot-pressing method, and combined theoretical estimation with experimental measurement to investigate the influence of Al doping on thermoelectric properties of SnSe. It was found that dopant Al can effectively adjust the band structure of SnSe by introducing intermediate band. Al doping with low content (x = 0.01 and 0.02) can introduce a single intermediate band close to the valence band maximum or conduction band minimum, achieving band engineering optimization. In high temperature region (498 K < T < 823 K), the electronic transport properties significantly enhance with thermal excitation. The lattice thermal conductivity reduces with the Al atomic point defect scattering, leading to a low thermal conductivity of 0.47 W m−1K−1 in Al0.04Sn0.96Se at 823 K. As a result, a high ZT of 0.84 at 823 K is obtained from the Al0.04Sn0.96Se perpendicular to the pressing direction, which is 58.5% larger than that of SnSe. In addition, dopant Al can adjust the anisotropy of polycrystalline SnSe. The anisotropy of electronic properties are enhanced with low doping level (x = 0.01, 0.02) and suppressed with high doping level (x = 0.03, 0.04).

Enhanced thermoelectric performance of hydrothermally synthesized polycrystalline Te-doped SnSe

In this study, large-scale Te-doped polycrystalline SnSe nanopowders were synthesized by a facile hydrothermal approach and the effect of Te doping on the thermoelectric properties of SnSe was fully investigated. It is found that the carrier concentration increases due to the reduction of band gap by alloying with Te, which contributes to significant enhancement of electrical conductivity especially at room temperature. Combined with the moderated Seebeck coefficient, a high power factor of 4.59 μW cm−1 K−2 is obtained at 773 K. Furthermore, the lattice thermal conductivity is greatly reduced upon Te substitution owing to the atomic point defect scattering. Benefiting from the synergistically optimized both electrical- and thermal-transport properties by Te-doping, thermoelectric performance of polycrystalline SnSe is enhanced in the whole temperature range with a maximum ZT of ∼0.79 at a relatively low temperature (773 K) for SnSe0.85Te0.15. This study provides a low-cost and simple low-temperature method to mass production of SnSe with high thermoelectric performance for practical applications

Excellent thermoelectricity performance of p-type SnSe along b axis

The electronic and thermoelectric properties of SnSe were calculated using the first-principles calculations and the semiclassical Boltzmann theory. The accurate electronic structure (calculated by the TB-mBJ) resulted in the trend changing between the Seebeck coefficient and the electrical conductivity, which were in good agreement with the experimental data. During the Pnma phase, the maximal zT value increased from 0.32 to 1.62 as the temperature rose. During the Cmcm phase, the maximal zT value increased from 4.03 to 4.33 as the temperature rose. The theoretical investigation provided valuable insight into the relationship between the electronic structure and thermoelectric transport properties of SnSe material.

The effect of Sm doping on the transport and thermoelectric properties of SnSe

SnSe has attracted much attention from scientific researchers because of its reported high ZT values. In this study, Sm doped p-type SnSe polycrystal is prepared through melting synthesis and high pressure (6.0GPa) sintering (HPS) method. The composition and microstructure of the samples was analyzed, and the thermoelectric transport properties were investigated in the temperature range of 303K to 823K. The results indicate that the electrical conductivity increases as Sm content increases. The Seebeck coefficient shows a decreasing trend with increasing Sm content. Due to the increase of alloy scattering, the total thermal conductivity decreases with increasing Sm content. The maximum power factor (PF) and ZTmax value are 214μWm−1K−2 and 0.55 for Sn0.97Sm0.03Se at 823K, respectively.

Insights into the thermoelectric properties of SnSe from ab initio calculations.

The thermoelectric properties of SnSe are studied by first-principles methods using an original methodology. We computed first the electronic structure of the system, which justifies its macroscopic anisotropy; the inclusion of van der Waals dispersive corrections improves the agreement of the structural parameters with experiments. The Seebeck coefficient and the electrical and thermal conductivities of single crystals and polycrystals are subsequently described in good agreement with experimental data. As for the electrical conductivity, values calculated with a temperature-dependent relaxation time compare well with the available measurements, especially for single crystals; in contrast, a constant relaxation time suffices to describe the results for polycrystals. Based on the iterative solution of the Boltzmann transport equation for phonons, we discuss the behavior of the thermal conductivity of the system in terms of its phonon spectrum. Finally, the figure of merit of SnSe single crystals and polycrystals is calculated and correlated with the previous discussions about electrical and thermal conductivities. From these findings, possible strategies to increase the figure of merit in practice are suggested.

Synthesis and Thermoelectric Properties of SnSe by Mechanical Alloying and Spark Plasma Sintering Method

The bulks of polycrystalline SnSe materials were successfully prepared by the mechanical alloying (MA) and spark plasma sintering (SPS) method. X-ray powder diffraction analysis showed that pure Sn and Se powders were synthesized into the SnSe phase by MA, and after SPS under 30–120 MPa, the single phase bulks of SnSe materials were successfully prepared. Scanning electron microcopy images displayed that the grain size of SnSe shows refinement with higher pressure. The electrical properties of the sintered samples increased with increasing sintering pressure. The thermal conductivity results show that the thermal conductivity remained low, in the range of 0.50–0.85 W m−1 K−1, with the different sintering pressure. The samples sintered under 100 MPa have the best thermoelectric properties; the dimensionless figure of merit ZT reached 0.71 at 873 K.

Enhanced thermoelectric performance of p-type SnSe doped with Zn

In this study, we have synthesized SnSe doped with zinc (Zn) and investigated the effect of Zn doping on the thermoelectric properties of SnSe. The results demonstrate that a high thermoelectric figure of merit (ZT) of 0.96 at 873K is obtained for Zn0.01Sn0.99Se, which is 41% higher than that of pure SnSe (ZT=0.68). The value is the highest value reported for p-type polycrystalline doped SnSe materials, which arises from the increased power factor coming from a high electrical conductivity and an enhanced Seebeck coefficient.

Optimization of Thermoelectric Performance of Anisotropic Ag x Sn1−x Se Compounds

SnSe is a promising thermoelectric material due to its ultralow thermal conductivity. However, stoichiometric SnSe compounds exhibit very low intrinsic defect concentration (3 × 1017 cm−3) and poor electrical transport properties, limiting the thermoelectric performance. In the present work, we investigated the effect of Ag dopant on the thermoelectric properties of SnSe. The results demonstrate that all the AgxSn1−xSe compounds exhibited anisotropic thermoelectric properties. The carrier concentration in the AgxSn1−xSe compounds greatly increased with increase of the Ag content, saturating at 1.9 × 1019 cm−3 for Ag0.01Sn0.99Se at room temperature. We found that a maximum zT value of 0.74 was obtained for Ag0.01Sn0.99Se perpendicular to the pressing direction at 823 K, being 23% higher than that of undoped SnSe (zT = 0.6).

A supercell approach to the doping effect on the thermoelectric properties of SnSe.

We study the thermoelectric properties of tin selenide (SnSe) by using first-principles calculations coupled with the Boltzmann transport theory. A recent experimental study showed that SnSe gives an unprecedented thermoelectric figure of merit ZT of 2.6 ± 0.3 in the high-temperature (>750 K) phase, while ZT in the low-temperature phase (<750 K) is much smaller than that of the high-temperature phase. Here we explore the possibility of increasing ZT in the low-temperature regime by carrier doping. For this purpose, we adopt a supercell approach to model the doped systems. We first examine the validity of the conventional rigid-band approximation (RBA), and then investigate the thermoelectric properties of Ag or Bi doped SnSe as p- or n-type doped materials using our supercell method. We found that both types of doping improve ZT and/or the power factor of the low-temperature phase SnSe, but only after the adjustment of the appropriate doping level is achieved.

The effect of Te doping on the electronic structure and thermoelectric properties of SnSe

SnSe 1− x Te x ( x =0, 0.0625) bulk materials were fabricated by melting Sn, Se and Te powders and then hot pressing them at various temperatures. The phase compositions of the materials were determined by X-ray diffraction (XRD) and the crystal lattice parameters were refined by the Rietveld method performed with DBWS. XRD analysis revealed that the grains in the materials preferentially grew along the (l 0 0) directions. The structural behavior of SnSe 1− x Te x ( x =0, 0.0625) was calculated using CASTEP package provided by Materials Studio. We found that the band gap of SnSe reduced from 0.643 to 0.608 eV after Te doping. The calculated results were in good agreement with experimental results. The electrical conductivity and the Seebeck coefficient of the as-prepared materials were measured from room temperature to 673 K. The maximum power factor of SnSe is ∼0.7 μW cm −1 K −2 at 673 K.