Structural phase transition of SnSe under uniaxial stress and hydrostatic pressure: an ab initio study

Alptekin, Sebahaddin

doi:10.1007/s00894-011-1019-2

Cited by 33 publications

(33 citation statements)

References 20 publications

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“…As temperature increases, there is a continuous phase transition towards the Cmcm phase, spreading over more than 200 K below the critical temperature of 807 K [3]. This transition can also be induced by pressure [56]. Our theoretically relaxed Cmcm lattice parameters are a ¼ 4.2838, b ¼ 4.2816, c ¼ 6.3250 Å, which also compare well to experimental data [1].…”

Section: -2supporting

confidence: 74%

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

et al. 2016

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The interest in improving the thermoelectric response of bulk materials has received a boost after it has been recognized that layered materials, in particular SnSe, show a very large thermoelectric figure of merit. This result has received great attention while it is now possible to conceive other similar materials or experimental methods to improve this value. Before we can now think of engineering this material it is important we understand the basic mechanism that explains this unusual behavior, where very low thermal conductivity and a high thermopower result from a delicate balance between the crystal and electronic structure. In this Letter, we present a complete temperature evolution of the Seebeck coefficient as the material undergoes a soft crystal transformation and its consequences on other properties within SnSe by means of first-principles calculations. Our results are able to explain the full range of considered experimental temperatures. DOI: 10.1103/PhysRevLett.117.276601 Thermoelectric (TE) materials and the thermoelectric effect are an interesting alternative energy source, harvesting waste heat from power production and other thermal engines. Despite their vast potential impact, only few materials are used in practice: most thermoelectric materials are highly toxic, expensive, and the devices present too low efficiencies to compete with other forms of power generation in industry. The main concern in this field is to discover or design thermoelectric materials that deal with these issues. The efficiency of a TE material is quantified by the thermoelectric figure of merit zT ¼ S 2 σT=ðκ el þ κ l Þ, which is the ratio of the electrical conductivity (σ), multiplied by the Seebeck coefficient (S) squared and the absolute temperature (T), over the thermal conductivity, which has both ionic (κ l ) and electronic (κ el ) contributions. The recent demonstration of zT ¼ 2.6 in monocrystalline tin selenide [1] or zT ¼ 1.34 in device form [2] has given a new breath to the field of thermoelectrics. By more than doubling the efficiency record for intrinsic bulk systems, SnSe has shown that economically competitive, nontoxic TE devices are within reach. The microscopic mechanism responsible for the performance is, however, not fully established, in particular due to sublimation effects in the high-T phase. Bulk SnSe is a narrowband-gap semiconductor that undergoes a phase transition spanning the temperature range from 600 to 807 K, from a Pnma low-temperature phase as illustrated in Fig. 1 (space group 62) to a Cmcm high-temperature phase (space group 63) [3]. Both are distorted phases of rocksalt Fm3m (the isoelectronic structure of PbTe and SnTe). Exceptional values of zT are obtained for two main reasons: the intrinsically low thermal conductivity (in both phases) and the strong enhancement of the carrier concentration and conductivity in the Cmcm phase. This intricate interplay opens perspectives for many other layered or heterostructure materials, and calls for a profound understanding of the mecha...

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Section: -2supporting

confidence: 74%

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

et al. 2016

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“…A systematic review of the vast literature on the high-pressure behaviour of group-IV chalcogenides is beyond the scope of this work, but we would like to highlight a few interesting cases. A pressure-induced transition from GeSto TlI-type phases is a recurring theme in recent computational work on GeS [28], GeSe [29], SnS [30], and SnSe itself [15]. X-ray diffraction studies on GeS [9] and GeSe [9,31] did not yield evidence of such a transition, but the quality of the experimental data would probably not have permitted detection of such a relatively subtle transition.…”

Section: Comparison With Related Systemsmentioning

confidence: 99%

“…Alptekin [15] predicted a pressure-induced second-order transition to a phase with space group Cmcm, isostructural with the high-temperature phase β-SnSe. Two possible phase transition pressures of 2 or 7 GPa were identified, depending on the method of calculation.…”

Section: Earlier High-pressure Studies Of Snsementioning

confidence: 99%

Structural changes in thermoelectric SnSe at high pressures

Loa

Husband

Downie

et al. 2015

J. Phys.: Condens. Matter

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Abstract. The crystal structure of the thermoelectric material tin selenide has been investigated with angle-dispersive synchrotron x-ray powder diffraction under hydrostatic pressure up to 27 GPa. With increasing pressure, a continuous evolution of the crystal structure from the GeS type to the higher-symmetry TlI type was observed, with a critical pressure of 10.5(3) GPa. The orthorhombic high-pressure modification, β -SnSe, is closely related to the pseudo-tetragonal high-temperature modification at ambient pressure. The similarity between the changes of the crystal structure at elevated temperatures and at high pressures suggests the possibility that strained thin films of SnSe may provide a route to overcoming the problem of the limited thermal stability of β-SnSe at high temperatures.

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“…Additional inaccuracies deal with the position of Se which sometimes has been assumed to have z ¼ 0 in Pnma, making some distances too short (Liu & Chang, 1992) or with cell parameters a, c in the high-temperature phase Cmcm which, due to lack of precision, are often found or constrained to be equal, rendering the cell 'pseudo-tetragonal' (Adouby et al, 1998;Wiedemeier & Csillag, 1979). Presumably, due to the fact that several studies have different cell-setting choices (Pnma, Pbnm, Pcmn), recent publications contain errors or ambiguities in reporting the cell parameters (Alptekin, 2011;Zhao et al, 2014). As an example Alptekin (2011) introduces the structure as being in Pnma, while later giving the cell in Pcmn.…”

Section: Introductionmentioning

confidence: 99%

“…Presumably, due to the fact that several studies have different cell-setting choices (Pnma, Pbnm, Pcmn), recent publications contain errors or ambiguities in reporting the cell parameters (Alptekin, 2011;Zhao et al, 2014). As an example Alptekin (2011) introduces the structure as being in Pnma, while later giving the cell in Pcmn. Zhao et al (2014) introduce the structure as being in Pnma, but in the unit-cell constants they revert b and c. In the same study the cell used for theoretical calculations appears to be the correct one, although the high-temperature phase is considered to be pseudo-tetragonal.…”

Section: Introductionmentioning

confidence: 99%

Crystal structure and phase transition of thermoelectric SnSe

Sist

Zhang

Iversen

2016

Acta Crystallogr B Struct Sci Cryst Eng Mater

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Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

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Structural phase transition of SnSe under uniaxial stress and hydrostatic pressure: an ab initio study

Cited by 33 publications

References 20 publications

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

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

Structural changes in thermoelectric SnSe at high pressures

Crystal structure and phase transition of thermoelectric SnSe

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