Highest ZT Value Research Articles

Magnetism Modulation for Cryogenic Thermoelectric Enhancements in Fe3O4 Nanoparticle-Incorporated Bi0.85Sb0.15 Nanocomposites.

The internal magnetism introduced by the magnetic nanoparticles combined with the external magnetic field can provide an effective way to modulate the thermoelectric (TE) properties of materials. Herein, we comparably investigate the effect of magnetism of Fe3O4 nanoparticles (Fe3O4-NPs) and the external magnetic field on the cryogenic thermoelectric properties of Fe3O4-NP/Bi0.85Sb0.15 nanocomposites. With the ferromagnetism-superparamagnetism transition, the Fe3O4-NPs in the superparamagnetic state exhibit a stronger magneto-trapped carrier effect, where the electron concentration at high temperature is evidently reduced. With the simultaneous increase of S and reduction of electronic thermal conductivity, a high ZT value of 0.33 at 180 K is obtained for 0.05 wt % Fe3O4/Bi0.85Sb0.15. Meanwhile, under the external magnetic field, the magnetoresistance of the composites is suppressed by Fe3O4-NPs, which results in a remarkable enhancement of the electronic transport performance. Consequently, the highest ZT value of 0.48 at 220 K under 1 T is achieved for 0.1 wt % Fe3O4-NPs/Bi0.85Sb0.15, increased by 55% compared with that of the matrix. A single-leg device is prepared using 0.1 wt % Fe3O4-NP/Bi0.85Sb0.15 nanocomposites. Its cooling temperature difference at 180 K reaches 1.3 and 3.2 K under 0 and 1 T when applying 300 mA current, increased by 20 and 46% compared with that of the matrix, respectively. This work suggests that magnetism modulation with introducing magnetic nanoparticles will enhance the TE and magneto-TE performance of composite materials.

Uplimit (ZT)max and effective merit parameter B* of thermoelectric semiconductors

Thermoelectric materials directly convert thermal energy and electrical power, attracting wide attention. New materials and new strategies to pursue a high ZT value mark the progress of thermoelectric materials. However, the critical factors relative to a given material's uplimit (ZT)max in the dual-parameter space of temperature carrier concentration are still an open question. In this work, we theoretically show that (ZT)max has a proximately linear relationship with B* that connects the weighted mobility, lattice thermal conductivity, and the bandgap in a single parameter. We also provide insight discussion for achieving a high B* by pursuing high U*, large Eg, and low κlat, or breaking the connections among κlat versus U*, Eg versus κlat, U* versus Eg, suggesting that B* is a good primary effective merit parameter for quick screening new thermoelectric materials.

Spin-polarized linear dispersions, lattice dynamics and transport properties of quaternary Heusler alloys (LiMgXSb)

In this study, we are predicting a new class of materials obtained by substituting a magnetic transition metal ion in quaternary Heusler alloys with the formula LiMgXSb (X = Co, Cr, Fe, Mn). We found that all the studied alloys exhibit a ferromagnetic ground state except LiMgCoSb. The phonon dispersions of the studied alloys computed within spin-polarized density functional perturbation theory (DFPT) do not exhibit any imaginary frequencies indicating that the proposed alloys are dynamically stable. The band structure calculations show that the studied alloys are metallic and exhibit the states near Fermi level for both spins. The fixed spin moment (FSM) calculations have been employed to exclude the possibility of other ferromagnetic ground states. One of the most interesting aspects of the band structure of these compounds is the existence of multiple band crossings leading to multiple Weyl points in the Brillouin zone. We have also computed the spin-polarized transport properties of these alloys. Our results find that doping charge carriers in the unit cell can significantly enhance the power factor and ZT. Electron doping is more effective for improving the power factor. Our findings show that among all the alloys LiMgFeSb has the highest ZT value with electron doping. Our studied materials constitute a new family of three-dimensional materials exhibiting band degeneracies that lead to Weyl points.

High mobility and excellent thermoelectric performance monolayer ZnX2Z4 (X = In, Al, Ga; Z = S, Se, Te) materials.

Recently, two-dimensional (2D) layered polarized ZnIn2S4 nanosheets have been successfully synthesized in experiments. However, the polarized monolayers are unstable in air, which hinders their practical applications. Therefore, in this work, we proposed a new family of nonpolarized monolayers (β2-phase) ZnX2Z4 (X = In, Al, and Ga; Z = S, Se, and Te) by first-principles. It is confirmed that the energies of β2-phase ZnX2Z4 are lower than those of the polarized and β-phase ZnX2Z4 monolayers. Moreover, these ZnX2Z4 monolayers have not only desirable indirect band gaps but also high electron mobility (up to 103 cm2 V-1 s-1), revealing a fascinating visible light absorption range. Furthermore, β2-phase ZnX2Te4 (X = In, Al, and Ga) has ultra-low lattice thermal conductivity and high ZT value (up to 0.89), suggesting that these monolayers can be good candidates for thermoelectric materials. These new 2D ternary monolayers not only effectively broaden the family of 2D materials but also provide promising candidates for optoelectronic and thermoelectric materials.

First-principles study on novel Fe-based quaternary Heusler alloys, with robust half-metallic, thermoelectric and optical properties.

This work aims are studying new and unique Fe-based quaternary Heusler alloys for data storage, energy conversion and optoelectronics applications. The structural, magnetic, mechanical, electrical, thermal, and optical properties of novel FeCrYZ (Y = Ti, Zr, & Hf and Z = Sn, and Sb) alloys have been theoretically explored making use of density functional theory (DFT). Except for FeCrHfSb, all the alloys are found to exhibit a stable ferromagnetic ground state during the energy minimization process, also half metallic ferromagnetism exhibiting 100% spin-polarization at the Fermi level obeying Slater-Pauling rule with total integer magnetic moments of 2.00μ B and 1.00μ B respectively. FeCrTiSn, FeCrTiSb and FeCrZrSb alloys have mechanical and dynamical stability under ambient conditions. Boltzmann transport theory was used to investigate the thermoelectric performance of the materials in the temperature range of 100-900 K. The estimated dimensionless figure of merit (ZT) for FeCrTiSb is 1.76, FeCrZrSb is 0.61, and FeCrHfSb is 0.86 at 900 K. Optical spectra reveal that absorption occurs across the visible and near UV ranges of the region. Results show that the narrow bandgap, spin polarization and high ZT value of FeCrTiSb make it a promising candidate for spintronic, thermoelectric and optoelectronic applications.

Physical, optoelectronic and thermoelectric characteristics of double perovskite (Sr2ScBiO6) for green energy technology using ab initio computations.

This work presents the investigation of physical characteristics including structural, electronic, elastic, optical and thermoelectric, of the double perovskite (DP) oxide Sr2ScBiO6 with the aid of the FP-LAPW method, dependent on DFT combined with BoltzTraP code. To incorporate the inclusion of exchange as well as correlation effects, approximations like LDA and three different forms of GGA [PBE-GGA, WC-GGA & PBEsol-GGA] are applied. The mBJ-GGA method including spin-orbital coupling (SOC) & not including SOC was utilised in this investigation and it was carried out in the WIEN2k code. In addition, the TB-mBJ exchange potential analysis classified Sr2ScBiO6 as having a p-type semiconducting nature with an indirect bandgap value of 3.327 eV. Additionally, the mechanical properties analysis and the related elastic constants demonstrate the anisotropic nature of Sr2ScBiO6 with decent mechanical stability. Apart from that, the Sr2ScBiO6 was considered a brittle non-central force solid with dominant covalent bonding. The varying optical parameter evaluations highlighted the potential use of Sr2ScBiO6 in visible-light (vis) and ultraviolet (UV)-based optoelectronic devices. Moreover, the semiconducting nature of Sr2ScBiO6 was verified through its thermoelectric response, which revealed that the charge carriers mostly consist of holes. Over a wide temperature range (100-1200 K), several transport metrics like the Seebeck coefficient (S), electrical conductivity (σ/τ), thermal conductivity (κ/τ), and power factor (PF) are investigated. An optimal value of figure of merit (ZT) ∼ 0.62 at T = 1200 K is accomplished. The extremely lower value of thermal conductivity as well as higher electrical conductivity leads to a higher figure of merit of the investigated system. The Sr2ScBiO6 verified a high ZT value, confirming that the material would be beneficial in renewable energy and thermoelectric (TE) applications.

Cryogenic thermoelectric enhancements in SbCl3-doped porous Bi0.85Sb0.15 alloys

The high ZT values of 0.45 under 0 T and 0.64 under 1 T at cryogenic temperature are achieved for a porous Bi0.85Sb0.15/1 vol% SbCl3 material prepared by SbCl3 sublimation due to a large decrease of thermal conductivity.

Vacancy Manipulation Induced Optimal Carrier Concentration, Band Convergence and Low Lattice Thermal Conductivity in Nano‐Crystalline SnTe Yielding Superior Thermoelectric Performance

AbstractSynergetic optimization of electrical and thermal transport properties is achieved for SnTe‐based nano‐crystalline materials. Gd doping is able to suppress the Sn vacancy, which is confirmed by positron annihilation measurements and corresponding theoretical calculations. Hence, the optimal hole carrier concentration is obtained, leading to the improvement of electrical transport performance and simultaneous decrease of electronic thermal conductivity. In addition, the incremental density of states effective mass m* in SnTe is realized by the promotion of the band convergence via Gd doping, which is further confirmed by the band structure calculation. Hence, the enhancement of the Seebeck coefficient is also achieved, leading to a high power factor of 2922 µW m−1 K−2 for Sn0.96Gd0.04Te at 900 K. Meanwhile, substantial suppression of the lattice thermal conductivity is observed in Gd‐doped SnTe, which is originated from enhanced phonon scattering by multiple processes including mass and strain fluctuations due to the Gd doping, scattering of grain boundaries, nano‐pores, and secondary phases induced by Gd doping. With the decreased phonon mean free path and reduced average phonon group velocity, a rather low lattice thermal conductivity is achieved. As a result, the synergetic optimization of the electric and thermal transport properties contributes to a rather high ZT value of ≈1.5 at 900 K, leading to the superior thermoelectric performance of SnTe‐based nanoscale polycrystalline materials.

Structural, vibrational, electronic, thermodynamic and thermoelectric properties of CaCdSi Half Heusler compound: A first-principles study

The new half-Heusler CaCdSi alloy, as a new crucial nonmagnetic thermoelectric candidate, is desired to be understood in terms of its potential physical properties and stability in both experimental and theoretical studies. Here we investigate the thermal properties of half-Heusler CaCdSi using the plane-wave pseudopotential approach based on the density functional theory within the generalized gradient approximation (GGA). Firstly, dynamical and mechanical stability was assured in its cubic phase. These results also elucidate the stable and brittle nature of the compound. Furthermore, electronic band structure calculation shows that the CaCdSi alloy has semiconductor behavior with a direct band gap of 0.59 eV. Lastly, the Seebeck coefficient, electronic conductivity, electronic thermal conductivity, the power factor, and figure of merit have been investigated using the semi-classical Boltzmann transport theory. The high value of ZT of the CaCdSi alloy makes it a potential candidate material for thermoelectric applications. Our research not only enriches the family of thermoelectric materials but also provides a good platform for further experimental investigations.

Electronic Structure, Optical and Thermal Response of Lead-Free RbAuBr3 and RbAuBr4 Perovskites for Renewable Energy Applications

The presence of toxic lead in the perovskites is the major hurdle in commercializing these novel materials-based devices. The first principles calculations have been conducted to investigate the electronic structure, optoelectronic, and transport properties of lead-free RbAuBr3 and RbAuBr4 perovskites. Modified Becke-Johnson approximation is used to evaluate the accurate band structures for both compounds. The calculated energy-volume curves and the negative formation energy values confirm their stability. The band structure profile shows a semiconductor nature of both compounds with bandgap values of 0.77 eV and 2.32 eV for RbAuBr3 and RbAuBr4, respectively. The density of states graphs endorsed the band structure results. The optical response is calculated in terms of real and imaginary parts of the dielectric function, refractive index, and energy loss parameters. The maximum absorption is achieved in the infrared region for RbAuBr3 and the visible region for RbAuBr4. The thermoelectric response is also computed and a high ZT value of 0.96 is achieved for RbAuBr3, while a moderate value of 0.60 is obtained for RbAuBr4 at 800 K. The calculated properties reveal the potential of studied lead-free perovskites for thermoelectric and optoelectronic applications.

Realizing high thermoelectric performance of Cu and Ce co-doped p-type polycrystalline SnSe via inducing nanoprecipitation arrays

Thermoelectric (TE) performance of polycrystalline stannous selenide (SnSe) has been remarkably promoted by the strategies of energy band, defect engineering, etc. However, due to the intrinsic insufficiencies of phonon scattering and carrier concentration, it is hard to simultaneously realize the regulations of electrical and thermal transport properties by one simple approach. Herein, we develop Cu and Ce co-doping strategy that can not only greatly reduce lattice thermal conductivity but also improve the electrical transport properties. In this strategy, the incorporated Cu and Ce atoms could induce high-density SnSe2 nanoprecipitation arrays on the surface of SnSe microplate, and produce dopant atom point defects and dislocations in its interior, which form multi-scale phonon scattering synergy, thereby presenting an ultralow thermal conductivity of 0.275 W·m-1·K-1 at 786 K. Meanwhile, density functional theory (DFT) calculations, carrier concentration, and mobility testing reveal that more extra hole carriers and lower conducting carrier scattering generate after Cu and Ce co-doping, thereby improving the electrical conductivity. The co-doped Sn0.98Cu0.01Ce0.01Se bulk exhibits an excellent ZT value up to ~1.2 at 786 K and a high average ZT value of 0.67 from 300 to 786 K. This work provides a simple and convenient strategy of enhancing the TE performance of polycrystalline SnSe.

Enhanced thermoelectric performance in n-type Mg3.2Sb1.5Bi0.5 doping with lanthanides at the Mg site

• Gd and Ho have increased the DOS of the valence band near the Fermi level, and the d electrons of Gd and Ho have made extraordinary contributions. • Gd and Ho are effective n-type cation site dopants with higher doping efficiency and better carrier concentration than the anion site dopants chalcogenide elements. • For Mg 3.2 Gd 0.02 Sb 1.5 Bi 0.5 and Mg 3.2 Ho 0.02 Sb 1.5 Bi 0.5 samples, we obtain high zT values of 1.61 and 1.55 at 725 K, respectively. • Gd as well as Ho are an alternative effective n-type doping element for higher thermoelectric performance. Mg-based thermoelectric materials have attracted more and more attention because of their rich composition elements, green environmental protection, and lower price. In recent years, the thermoelectric properties of n-type Mg 3 Sb 2 materials have been optimized by doping chalcogenide elements (S, Se, and Te) at the anionic position. In this work, n-type Mg 3.2 A x Sb 1.5 Bi 0.5 ( A = Gd, Ho; x = 0.01, 0.02, 0.03, and 0.4) samples were prepared by the cation site doping of lanthanide elements (Gd and Ho). The research results show that Gd and Ho doped n-type Mg 3.2 Sb 1.5 Bi 0.5 samples are entirely comparable to the S, Se, and Te doped n-type Mg 3.2 Sb 1.5 Bi 0.5 samples, demonstrating more excellent thermoelectric properties. Doping with lanthanides (Gd and Ho) at the Mg site increases the carrier concentration of the material to 8.161 × 10 19 cm −3 . Doping induces the contribution of more electron, thus obtaining higher conductivity. The maximum zT value of the Mg 3.2 Gd 0.02 Sb 1.5 Bi 0.5 and the Mg 3.2 Ho 0.02 Sb 1.5 Bi 0.5 samples reaches 1.61 and 1.55, respectively. This work theoretically and experimentally demonstrates Gd and Ho are efficient n-type dopants for Mg 3.2 Sb 1.5 Bi 0.5 thermoelectric material.

Enhanced thermoelectric performance of 3D-printed Bi2Te3-based materials via adding Te/Se

Bi2Te3-based materials were prepared by direct ink writing (DIW) 3D printing and their microstructure and thermoelectric properties were investigated with an emphasis on the effect of the content of DMF and Te/Se addition. As the mass ratio of DMF in the composition increased from 6.5% to 8.0% (in mass), the electrical conductivity deteriorated because of the corresponding increased porosity and organic remains in the samples. However, the volatilization of DMF would reduce the fluidity of the slurry. Thus, thermoelectric slurry with 7.0% DMF is the most suitable mass ratio for 3D printing. Additionally, adding Te in the p-type Bi0.4Sb1.6Te3 and adding Se in the n-type Bi2Te2.6Se0.4 have significantly improved their electrical conductivity due to the increased carrier concentration and mobility. Combining with the moderate Seebeck coefficient (∼200 μV/K), high power factors with ∼802 μW·m−1·K−2 and 1266 μW·m−1·K−2 were obtained for the n-type Bi2Te2.6Se0.4+10%Se and p-type Bi0.4Sb1.6Te3+7%Te, respectively, which result in the final relatively high zT values of 0.68 at 573 K and 0.56 at 330 K for n-type and p-type 3D-printed samples.

First principle studies on electronic and thermoelectric properties of Fe2TiSn based multinary Heusler alloys

The alloys with 8/18/24 valence electron count (VEC) are promising candidates for efficient energy conversion and refrigeration applications at low as well as high temperatures. Recently Fe-based Heusler alloys attracted researchers due to their compelling electronic band structure i.e flat band along one direction of the Brillouin zone and highly dispersive bands along the other directions. Here we focus on the thermoelectric (TE) transport properties of isovalent/aliovalent substituted Fe2TiSn systems those may be potential TE materials. The multinary substitution has been done in such a way that it preserves the 24 VEC and hence the semiconducting nature. The calculated total energies with VASP-PAW potential within density functional theory with PBE-GGA functional were used to determine the ground state properties such as equilibrium lattice parameters, bulk modulus etc. We have also investigated the structural, electronic, lattice dynamic and TE transport properties by using PBE-GGA and TB-mBJ exchange–correlation functional. The full potential linearized augmented plane wave method as implemented in WIEN2k code was used to investigate electronic structure and TE transport properties with the PBE-GGA and TB-mBJ exchange potentials and Boltzmann transport theory. The calculated single crystal elastic constants, phonon dispersion and phonon density of states confirm that these systems are mechanically and dynamically stable. The TE transport properties is calculated by including the lattice part of thermal conductivity (κL) obtained from two methods one from the calculated elastic properties calculation (κLelastic) and the other from phonon dispersion curve (κLphonon). The strong phonon–phonon scattering by large mass difference/strain fluctuation of isovalent/aliovalent substitution at Ti/Sn sites of Fe2TiSn reduces the lattice thermal conductivity which results in high thermoelectric figure-of-merit (ZT) value of 0.81 at 900K for Fe2Sc0.25Ti0.5Ta0.25Al0.5Bi0.5. The comparative analysis of TE transport properties using the band structures calculated with the PBE-GGA and TB-mBJ functional shows that the ZT value obtained from TB-mBJ scheme is found to be significantly higher than that based on PBE-GGA. The calculated relatively low lattice thermal conductivity and high ZT values suggest that isovalent/aliovalent substituted Fe2TiSn are promising candidates for medium to high temperature waste heat recovery.

Fast preparation of AgxPb20SbTe20 (x = 0.5–3) component with high thermoelectric performance

PbTe-based quaternary AgPbmSbTem+2 (LAST) has been a kind of promising thermoelectric materials due to its relatively low lattice thermal conductivity and good electrical performance. However, traditional melting or mechanical alloying methods are time-consuming, which is not suitable for applications. To solve this problem, a fast method combined self-propagating high-temperature synthesis (SHS) with spark plasma sintering (SPS) has been adopted in this work. Nanostructured n-type AgxPb20SbTe20 (x = 0.5–3) materials with high thermoelectric performance have been successfully prepared. On one hand, power factors of all samples reached over 1.6 mW·m−1·K−2 at high temperature, because Ag assembles grain boundaries and forms Ag2Te precipitates in the SHS process, enhancing the thermoelectric properties by modulation doping, energy filtering and dynamic doping. On the other hand, the Ag2Te-PbTe coherent interfaces bring multiple phonon scattering resources to reduce the thermal conductivity. As a result, a high ZT value of ∼1.32 at 773 K is achieved in Ag1.25Pb20SbTe20. This work provides a facile, rapid and energy-saving way to prepare PbTe-based materials with good thermoelectric performance.

Effects of different Bismuth concentrations of InSbBi crystals grown by Bridgman technique

InSb1-xBix (x = 0, 0.005, 0.010, 0.015) crystals are grown by vertical Bridgman technique using single-zone resistive heating furnace. The main objective of this paper is to study the improvement of thermoelectric quality factors by different concentrations of Bismuth (Bi) in InSbBi crystals. EDAX (Energy Dispersive Analysis of X-rays) confirms that the grown crystals are pure and show the presence of In, Sb, and Bi in proportion. Powder X-ray diffractogram confirms the cubic zinc blend structure of these crystals with space group F-43m and all the diffraction peaks are matched well to the standard JCPDS-ICDD No. 6-0208. Raman spectra are recorded from 80 K to 300 K and Raman mapping spectra at room temperature for all above crystals have shown the presence of TO mode at 179.91 cm−1 and LO mode at 190.16 cm−1. The sharpness and intensity of Raman spectra have clearly reflected the purity and quality of the grown crystals. The electrical conductivity σ is found to increase slowly upto 450 K and then increases linearly upto 600 K and above that, it gets saturated in all crystals. The Seebeck coefficient remains negative showing that these crystals are n-type semiconductor and its value is found to be increased to −200 μV/K for InSb0.985Bi0.015 in comparison to −150 μV/K for pure InSb near 600 K. From the lattice thermal conductivity, power factor and thermoelectric figure of merit i.e. ZT calculations, it is concluded that InSb0.985Bi0.015 at 670 K gives the highest value of ZT = 0.45 in comparison to other grown crystals.

Engineering Interfacial Effects in Electron and Phonon Transport of Sb2Te3/MoS2 Multilayer for Thermoelectric ZT Above 2.0

AbstractEfficient thermoelectric (TE) conversion of waste heat to usable energy is a holy grail promising to address major societal issues related to energy crisis and global heat management. For these to be economical, synthesis of a solid‐state material with a high figure‐of‐merit (ZT) values is the key, with characterization methods quantifying TE and heat transport properties being indispensable for guiding the development of such materials. In the present study, a large enhancement of the TE power factor in Sb2Te3/MoS2 multilayer structures is reported. A new approach is used to simultaneously experimentally determine the values of in‐plane (kxy) and out‐of‐pane (kz) thermal conductivities for multilayer samples with characteristic layer thickness of few nanometres, essential for the quantification of the ZT, the key parameter for the TE material. Combining simultaneous enhancement in the value of in‐plane power factor (to (4.9 ± 0.4) × mWm−1 K−2) and reduction of the in‐plane value of the thermal conductivity (to 0.7 ± 0.1 Wm−1 K−1) for Sb2Te3/MoS2 multilayer sample led to high values of ZT of 2.08 ± 0.37 at room temperature. The present study, therefore, sets the foundation for a new methodology of exploiting the properties of 2D/3D interfaces for the development of novel fully viable thermoelectric materials.

Thermoelectric transport properties of n-type layered homologous (Bi2)m(Bi2Se3)n compounds

This work experimentally showed that the homologous heterostructure (Bi2)m(Bi2Se3)n compounds of Bi4Se3 (m = 1, n = 1), Bi8Se7 (m = 5, n = 7), BiSe (m = 1, n = 2), and Bi8Se9 (m = 1, n = 3) are promising TE materials, with low lattice thermal conductivity (<0.8 W m−1 K−1) due to the bismuth bilayer. Each compound with pure phase can be obtained by using the simple method of mechanical alloying and spark plasma sintering. All of them show a high electrical conductivity over 1000 S cm−1 and relatively low Seebeck coefficient below 100 μV K−1 due to the high carrier concentration. However, the electrical conductivity gradually decreases with reducing the ratio of m to n from Bi4Se3 (m = 1, n = 1) to Bi8Se7 (m = 5, n = 7), BiSe (m = 1, n = 2) and Bi8Se9 (m = 1, n = 3) due to the reduced proportion of the [Bi2] layers in per crystal cell, while reverse for the change of the Seebeck coefficient. Thus, a relative high power factor with ∼8.0 μW cm−1 K−2 were obtained for BiSe and Bi8Se9. Therefore, combining with the low thermal conductivity, a maximum ZT of ∼0.3 at 623 K was obtained for Bi8Se9. Higher ZT values can be expected by further properly optimizing their electrical transport property using doping or alloying.

Electronic structure and thermoelectric properties of uniaxial strained SnSe from first-principles calculations

SnSe is a promising candidate of thermoelectric material for its high ZT value. To further optimize its thermoelectric performance, we systematically investigate the uniaxial strain dependence of electronic structure and thermoelectric properties for both p- and n-type SnSe based on first-principles calculations and Boltzmann transport equation. The band gap of SnSe can be significantly tuned by the uniaxial strain along b-axis. The momentum alignment and energy convergence of band structure induced by uniaxial strains are observed. The Seebeck coefficient, electrical conductivity and power factor can be significantly improved by applying suitable uniaxial strains. In particular, for p-type SnSe at 300 K, the peak value of PFxx/τ for εa = −6% is 7.6 times as large as that of unstrained SnSe. The peak values of PFxx/τ, PFyy/τ and PFzz/τ in p-type SnSe at 300 K under εb = −6% are 2.6, 2.0 and 2.3 times as large as those of unstrained SnSe, respectively. At 750 K, the peak value of PFzz/τ increases by 96.9% under εc = −6% in p-type SnSe and the peak value of PFyy/τ increases by 73.2% under εb = 6% in n-type SnSe. Our findings indicate that uniaxial strain can be an efficient strategy to modulate the thermoelectric properties of SnSe and provide a helpful perspective for its practical applications.

Phonon Scattering Mechanism for Size‐Dependent Thermoelectric Properties of Bi2Te3 Nanoparticles

AbstractThe effect of nanoparticle size on thermoelectric properties of Bi2Te3 nanoparticles is theoretically analysed using a phonon scattering mechanism. The size‐dependent thermoelectric properties in Bi2Te3 nanoparticles give an opportunity to tune the nanoparticles′ size, which helps to optimize the figure of merit (ZT=S2σT/κ). The thermoelectric effect in Bi2Te3 nanoparticles is investigated using the phonon scattering effect. Reduction in nanoparticle size increases interface volume ratio, which increases the scattering of phonons with grain boundaries. An increase in phonon‐grain boundary scatterings decreases the thermal conductivity (κ) due to the shortening of the phonon mean free path. The Seebeck coefficient (S) and simultaneously ZT increase significantly because of a decrease in lattice thermal conductivity. The highest value of ZT=0.45 is obtained at temperature T=400 K for 150 nm Bi2Te3 nanoparticles, which has been enhanced up to ZT=0.92 by reducing the nanoparticles size up to 30 nm at the same temperatures. The results obtained from the present model are in good agreement with the experimental data and reflect that the thermoelectric properties are dominated by the phonon scattering mechanism and depend on the density of interfaces in the material. Numerical analysis of thermoelectric properties from the present investigation will help in designing efficient thermoelectric materials.