Two-Step Phase Transition in SnSe and the Origins of its High Power Factor from First Principles

Dewandre, Antoine; Hellman, Olle; Bhattacharya, Sandip; Romero, Aldo H.; Madsen, Georg K. H.; Verstraete, Matthieu J.

doi:10.1103/physrevlett.117.276601

Cited by 102 publications

(96 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…As can be seen in figure 2, when reducing the number of layers, the in-plane lattice parameters (a and b) converge, and are almost identical for the monolayer case of SnSe. This behaviour mirrors experimental studies on heterostructures containing SnSe slabs [32] and the high-temperature behaviour of both compounds [3,4]. The monolayer of SnS also rectifies, but its a/b ratio does not converge to 1: we find a small dynamical instability for perfect square in-plane parameters (see Supplemental information).…”

Section: Few-layer Structuressupporting

confidence: 86%

“…Chalcogenides are a remarkable family of layered materials, displaying an extensive range of optical, electronic, thermal and mechanical effects [1]. They are used as phase-change materials in rewritable data storage [2], as high performance thermoelectrics [3,4], and as absorbing layers in photovoltaic cells [5][6][7]. Lead (Pb) chalcogenides and their alloys have been heavily studied for their excellent thermoelectric properties [8][9][10][11] but the presence of toxic chemical elements is a major industrial disadvantage.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spectroscopic properties of few-layer tin chalcogenides

et al. 2019

Self Cite

View full text Add to dashboard Cite

Stable structures of layered SnS and SnSe and their associated electronic and vibrational spectra are predicted using first-principles DFT calculations. The calculations show that both materials undergo a phase transformation upon thinning whereby the in-plane lattice parameters ratio a/b converges towards 1, similar to the high-temperature behaviour observed for their bulk counterparts. The electronic properties of layered SnS and SnSe evolve to an almost symmetric dispersion whilst the gap changes from indirect to direct. Characteristic signatures in the phonon dispersion curves and surface phonon states where only atoms belonging to surface layers vibrate should be observable experimentally.

show abstract

Section: Few-layer Structuressupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Spectroscopic properties of few-layer tin chalcogenides

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…In contrast, there is no big difference in electrical conductivity for the SnCl 2 -doped SnSe sample in this temperature range. [24] This means that the increase in carrier concentration is due to the creation of additional Sn vacancies during the phase transition. The rapid increase in the electrical conductivity above 600 K is mainly ascribed to the structural transition from Pnma to Cmcm, according to the neutron and synchrotron diffraction results (Figure 2,3,4).…”

Section: Thermoelectric Properties Of Pristine Ag-and Sncl 2 -Doped mentioning

confidence: 99%

Three‐Stage Inter‐Orthorhombic Evolution and High Thermoelectric Performance in Ag‐Doped Nanolaminar SnSe Polycrystals

Zhang

Wang

Sun

et al. 2017

Advanced Energy Materials

View full text Add to dashboard Cite

generation in deep-space and waste heat recovery from vehicle exhaust, as well as ice-free refrigeration in wine-storage cabinets, hotel room mini-refrigerators, and office water coolers. [1][2][3][4][5] The performance of TE materials is determined by the dimensionless figure of merit (ZT), defined as ZT = α 2 σT/(κ lat + κ ele ), where α, σ, κ lat , κ ele , and T are the Seebeck coefficient, electrical conductivity, lattice thermal conductivity, electronic thermal conductivity, and absolute temperature, respectively. The conversion efficiency for these potential applications requires high ZT over a wide range of temperatures. [6] For effective waste heat recovery in vehicles under a 350 K temperature differential, the average or device ZT (ZT dev ) should be about 1.25 in order to increase mileage up to 10%, [1,7] while for primary power generation, an average ZT of more than 1.5 is required under an 800 K temperature differential. [1,7] Recently, SnSe single crystals have produced a surge in the field of thermoelectrics as a new type of promising TE materials because of the intrinsically ultralow thermal conductivity (<0.4 W m −1 K −1 at 923 K) and high ZT along the b-and c-crystallographic directions (>2.3 at 923 K). [8] A new record of ZT dev ≈ 1.34 from 300-773 K along the b-crystallographic direction was achieved in thermoelectric device fabricated from hole-doped SnSe single crystal. [9] Nevertheless, the difficulties in large-scale synthesis of single crystals limit their practical applications, and extensive efforts have been devoted to the fabrication of high-performance polycrystalline counterparts. [10][11][12][13][14][15] For example, Wei et al. [12] reported a ZT of ≈0.8 at 800 K in 1% Na-and K-doped SnSe, which was produced by conventional solid state reaction followed by a spark plasma sintering (SPS) treatment. Due to an impressively low lattice thermal conductivity (≈0.20 W m −1 K −1 at 773 K) arising from the presence of coherent nanoprecipitates in the SnSe matrix, a high ZT of ≈1.1 at 773 K was achieved in the direction perpendicular to the pressing direction of SPS for ball-milled K-doped SnSe. [11] Apart from p-type alkali dopants (Li, Na, K), n-type dopants such as I and BiCl 3 are also adopted to improve the performance of polycrystalline SnSe. [14,16] For instance, a ZT of ≈0.8 at 773 K was obtained in I-doped SnSe polycrystals, whichThe ultrahigh thermoelectric performance of SnSe-based single crystals has attracted considerable interest in their polycrystalline counterparts. However, the temperature-dependent structural transition in SnSe-based thermoelectric materials and its relationship with their thermoelectric performance are not fully investigated and understood. In this work, nanolaminar SnSe polycrystals are prepared and characterized in situ using neutron and synchrotron powder diffraction measurements at various temperatures. Rietveld refinement results indicate that there is a complete inter-orthorhombic evolution from Pnma to Cmcm by a series of layer slips and stretches a...

show abstract

“…Additionally, theoretical predictions based on the Boltzmann formalism indicate an increase of the electrical conductivity with temperature -arising from the thermal excitation of carriers across the Fermi surface -which is in stark contrast with experimental observations, where a pronounced reduction of charge conduction with increasing temperature has been observed [5].These findings seem to suggest a strong interplay between electronic and ionic degrees of freedom. While recent theoretical works have thus far provided a comprehensive investigation, based on first-principles calculations, of quasiparticle bands [15], defect formation energies [16], crystal-lattice dynamics [17], lattice anharmonicities [4], electron-phonon interaction [18], and transport properties [15,19,20], unraveling the origin of the peculiar temperature-dependent properties of this high-performance thermoelectric continues to represent a major challenge.In this work, we tackle the temperature-induced renormalization of the electronic and transport properties of SnSe by combining, within a first-principles framework, the many-body theory of the electron-phonon interaction in the Fan-Migdal approach and the Boltzmann transport formalism beyond the constant relaxation time, including effects of the lattice expansion. We find a strong enhancement of the electron-phonon coupling strength with temperature which stems from the thermal excitation of soft polar modes and manifests itself through band-structure renormalization effects, an increase of electron linewidths by a factor of five between 0 and 600 K, and a highlyanisotropic renormalization of the hole effective mass.…”

mentioning

confidence: 99%

“…[5]. For the undoped SnSe, we assume a hole concentration of 4.5 · 10 17 cm −3 to account for the additional carriers induced by the formation of Sn vacancies [20]. The results obtained for the crystallographic axis a are shown in Fig.…”

mentioning

confidence: 99%

Thermally enhanced Fröhlich coupling in SnSe

et al. 2019

View full text Add to dashboard Cite

To gain insight into the peculiar temperature dependence of the thermoelectric material SnSe, we employ many-body perturbation theory and explore the influence of the electron-phonon interaction on its electronic and transport properties. We show that a lattice dynamics characterized by soft highly-polar phonons induces a large thermal enhancement of the Fröhlich interaction. We account for these phenomena in ab-initio calculations of the photoemission spectrum and electrical conductivity at finite temperature, unraveling the mechanisms behind recent experimental data. Our results reveal a complex interplay between lattice thermal expansion and Fröhlich coupling, providing a new rationale for the in-silico prediction of transport coefficients of high-performance thermoelectrics.The discovery of the record-breaking thermoelectric properties of SnSe has laid a new milestone in the quest for high-efficiency thermoelectric materials [1]. SnSe combines large carrier conductivity σ and Seebeck coefficient S, with highly anharmonic lattice dynamics [2-4]. Anharmonic effects limit the lattice thermal conductivity κ via phonon-phonon scattering, thus contributing to a record-high figure of merit ZT = (S 2 σ/κ)T ∼ 2.6, which may be even further improved through doping and alloying [5][6][7][8].As the operational conditions of thermoelectric devices typically involve large temperatures, a quantummechanical description of the electronic and lattice properties of SnSe across the temperature domain of its thermodynamical stability is key to unravel the microscopic origin of this outstanding thermoelectric performance. Recent experimental investigations have unveiled a pervasive influence of temperature on the electronic and transport properties of SnSe. Angle-resolved photoemission spectroscopy experiments, for instance, have reported (i) a pronounced dependence of the peak linewidth on the sample temperature [9], (ii) the emergence at low temperature of a gap between the first two occupied bands at the Z point, [10][11][12][13], and (iii) a non-monotonic effective-mass renormalization as a function of temperature [14]. Density-functional theory calculations fail at unraveling the origin of these phenomena. Additionally, theoretical predictions based on the Boltzmann formalism indicate an increase of the electrical conductivity with temperature -arising from the thermal excitation of carriers across the Fermi surface -which is in stark contrast with experimental observations, where a pronounced reduction of charge conduction with increasing temperature has been observed [5].These findings seem to suggest a strong interplay between electronic and ionic degrees of freedom. While recent theoretical works have thus far provided a comprehensive investigation, based on first-principles calculations, of quasiparticle bands [15], defect formation energies [16], crystal-lattice dynamics [17], lattice anharmonicities [4], electron-phonon interaction [18], and transport properties [15,19,20], unraveling the origin of the peculiar tempera...

show abstract

Two-Step Phase Transition in SnSe and the Origins of its High Power Factor from First Principles

Cited by 102 publications

References 57 publications

Spectroscopic properties of few-layer tin chalcogenides

Spectroscopic properties of few-layer tin chalcogenides

Three‐Stage Inter‐Orthorhombic Evolution and High Thermoelectric Performance in Ag‐Doped Nanolaminar SnSe Polycrystals

Thermally enhanced Fröhlich coupling in SnSe

Contact Info

Product

Resources

About