Prediction of the stability of the rhombohedral phase in IV–VI monochalcogenides and its origin

Argaman, Uri; Abutbul, Ran E.; Segev, Elad; Makov, Guy

doi:10.1039/c7ce01374d

Cited by 15 publications

(15 citation statements)

References 28 publications

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“…This structure consists of arrays of double-tetrahedra with a Ge–S = 2.52–2.63 Å and long intralayer Ge–S bonds at a Ge–S ′ = 2.93 Å, as shown in Figure g. The GA search found a rhombohedral phase in Figure i similar to GeTe and GeSe that was studied previously in ref . This rhombohedral GeS has a formation energy on par with the P 4̅3 m phase, but a negative phonon mode near Γ indicates dynamical instability.…”

Section: Resultssupporting

confidence: 53%

“…To compare with the phases predicted by GA, we consider several additional structures of GeS that include β-Cmcm, πcubic P2 1 3 (large unit cell of 64 atoms) based on SnS and SnSe nanoparticles, 16 rhombohedral R3m based on GeTe and GeSe, 17 and the rock salt structure. The phonon spectra of the novel phases were calculated and are reported in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

“…Recently, the related compounds of SnS, GeSe, and SnSe have been found to present rich phase diagrams beyond the α- Pnma ambient state by considering pressure and nanoscale modifications. These contain the Cmcm phase at high temperature or high pressure, monoclinic P 2 1 / m in compressed SnS, exotic non-centrosymmetric π-cubic P 2 1 3 found in SnS and SnSe, and possibly a non-centrosymmetric rhombohedral phase predicted in SnSe and GeSe. , Recently, SnSe and GeSe were found to form an additional new Pnma structure. , Meanwhile, the known phase diagram of GeS remains simple. Only two other GeS phases have been reported in the literature at high pressures: phase II ( P 2 1 / m ) at ∼9 GPa and phase III ( Cmcm ) at ∼32 GPa .…”

Section: Introductionmentioning

confidence: 99%

“…These contain the Cmcm phase at high temperature or high pressure, 14 monoclinic P2 1 /m in compressed SnS, 15 exotic non-centrosymmetric π-cubic P2 1 3 found in SnS and SnSe, 16 and possibly a non-centrosymmetric rhombohedral phase predicted in SnSe and GeSe. 17,18 Recently, SnSe and GeSe were found to form an additional new Pnma structure. 19,20 Meanwhile, the known phase diagram of GeS remains simple.…”

Section: Introductionmentioning

confidence: 99%

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GeS Phases from First-Principles: Structure Prediction, Optical Properties, and Phase Transitions upon Compression

Nguyen

Makov

2022

Crystal Growth & Design

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The structures of GeS beyond the orthorhombic α-Pnma phase are explored by density functional theory calculations of the energetics and phonon spectra guided by an evolutionary algorithm. We found six new, dynamically stable structures at ambient conditions, close to the ground state. Our study of the electronic and optical properties of these unconventional phases indicates distinct differences from α-Pnma GeS. The band gaps of the new phases vary in the range of 0.39–1.59 eV, and their optical properties are attractive for optoelectronic applications. Upon compression, the new GeS structure denoted as γ-Pnma (analog to γ-Pnma SnSe) is thermodynamically preferred over α-Pnma at 15 GPa. At higher pressures, the GeS structure converges to a Cmcm-like structure at 30 GPa. Finally, cubic Pm3̅m is the favorable and stable phase at 70 GPa. The mechanism of the pressure-induced transition correlates with the delocalization of the lone pairs.

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Section: Resultssupporting

confidence: 53%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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GeS Phases from First-Principles: Structure Prediction, Optical Properties, and Phase Transitions upon Compression

Nguyen

Makov

2022

Crystal Growth & Design

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“…17. Conversely, c-GeSe occurs in a orthorhombic P nma symmetry up to the melting point at 667 • C 18,19 .…”

Section: Introductionmentioning

confidence: 99%

Alteration of structural, electronic, and vibrational properties of amorphous GeTe by selenium substitution: An experimentally constrained density functional study

et al. 2021

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The structural, vibrational and electronic properties of several compositions of amorphous Ge-Se-Te are studied from a combination of X-ray diffraction and density functional-based molecular dynamics. Different structural properties are considered such as structure factors, pair distribution functions, angular distributions, coordination numbers and neighbor distributions. We compare results with experimental findings and a satisfying agreement is found for the structure functions in real and reciprocal spaces. The short range order is found to be more complex than in related binaries that result in mixed geometries ( 65-75 % tetrahedral, and remaining defect octahedral) for a dominant four-fold Ge (80 %). The chalcogen atoms are dominantly 2-fold, the former having furthermore an important fraction of 3-fold coordinated atoms (30-40 %). The obtained model structures indicate that Ge-Ge, Ge-Se, and Ge-Te bonds dominate with small fractions of Te-Te bonds remaining from the base system GeTe. The investigation of electronic properties indicates that the addition of Se atoms will lead to Te-related bands that are much more localized so that Ge-Te-Se can be regarded as having an increased covalent character with respect to GeTe.

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π‐Phase Tin and Germanium Monochalcogenide Semiconductors: An Emerging Materials System

et al. 2018

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Cubic π-phase monochalcogenides (MX, M = Sn, Ge; X = S, Se) are an emerging new class of materials that has recently been discovered. Here, their thermodynamic stability, progress in synthetic routes, properties, and prospective applications are reviewed. The thermodynamic stability is demonstrated through density functional theory total energy and phonon spectra calculations, which show that the π-phase polytype is stable across the monochalcogenide family. To date, only π-phase tin monochalcogenides have been observed experimentally while π-phase Ge-monochalcogenides are predicted to be stable but are yet to be experimentally realized. Various synthetic preparation protocols of π-SnS and π-SnSe are described, focusing on surfactant-assisted nanoparticle synthesis and chemical deposition of thin films from aqueous-bath compositions. These techniques provide materials with different surface energies, which are likely to play a major role in stabilizing the π-phase in nanoscale materials. The properties of this newly discovered family of semiconducting materials are discussed in comparison with their conventional orthorhombic polymorphs. These could benefit a number of photovoltaic and optoelectronic applications since, apart from being cubic, they also possess characteristic advantages, such as moderately low toxicity and natural abundance.

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Prediction of the stability of the rhombohedral phase in IV–VI monochalcogenides and its origin

Abstract: Rhombohedral GeSe and SnSe are predicted to be the stable ground state structures.

Cited by 15 publications

References 28 publications

GeS Phases from First-Principles: Structure Prediction, Optical Properties, and Phase Transitions upon Compression

GeS Phases from First-Principles: Structure Prediction, Optical Properties, and Phase Transitions upon Compression

Alteration of structural, electronic, and vibrational properties of amorphous GeTe by selenium substitution: An experimentally constrained density functional study

π‐Phase Tin and Germanium Monochalcogenide Semiconductors: An Emerging Materials System

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