Ionic Conductivity and Tracer Diffusion in Glassy Chalcogenides

Alekseev, I. E.; Fontanari, Daniele; Sokolov, Anton; Bokova, Maria; Kassem, Mohammad; Bychkov, Eugene

doi:10.1142/9789811215575_0008

Cited by 9 publications

(24 citation statements)

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“…%, the cation distribution is nonrandom, visible both in macroscopic characteristics as the Haven ratio in 108m,110m Ag and 204 Tl tracer diffusion and structural studies using time-of-flight neutron diffraction and high-energy X-ray scattering. 61 The diffraction results were supported by AIMD simulations revealing that 20−28% of the sulfur does not have direct chemical bonding to germanium (we call them isolated S species, S iso ) and connected only to cations, [M]/[S iso ] ≈ 2. The isolated sulfur is known for crystalline metal chalcogenides.…”

Section: Resultsmentioning

confidence: 73%

“…Our recent studies of silver and thallium thiogermanate glasses within a similar composition range, (M 2 S) x (GeS 2 ) 1– x , 0 ≤ x ≤ 0.5, have also shown that, at above 10 at. %, the cation distribution is non-random, visible both in macroscopic characteristics as the Haven ratio in 108m,110m Ag and 204 Tl tracer diffusion and structural studies using time-of-flight neutron diffraction and high-energy X-ray scattering . The diffraction results were supported by AIMD simulations revealing that 20–28% of the sulfur does not have direct chemical bonding to germanium (we call them isolated S species, S iso ) and connected only to cations, [M]/[S iso ] ≈ 2.…”

Section: Results and Discussionmentioning

confidence: 82%

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Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

et al. 2020

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Glasses in the pseudo-binary system (HgS) x (GeS2)1–x were synthesized over the concentration range of 0.0 ≤ x ≤ 0.5. The fundamental glass properties (macroscopic, electric, and vibrational) were studied using differential scanning calorimetry (DSC), direct current (dc) electrical measurements, Raman spectroscopy supported by DFT modeling, and X-ray diffraction. Mercury species in thiogermanate glasses essentially form chain-like (HgS2/2) fragments substituting bridging sulfur between corner- and edge-sharing GeS4/2 tetrahedra. This structural evolution results in a significant monotonic decrease of the glass transition temperatures from 480 to 270 °C. The room-temperature dc conductivity changes non-monotonically with increasing HgS content x over a limited range of 4 × 10–15 to 7 × 10–13 S cm–1. The electronic transport in insulating HgS-GeS2 glasses occurs via extended electronic states. Tetrahedral HgS4/4 fragments also appear in the glass network with increasing x. Their exact population needs further advanced structural studies using diffraction techniques.

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Section: Resultsmentioning

confidence: 73%

Section: Results and Discussionmentioning

confidence: 82%

Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

et al. 2020

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“…The cubic lattice of argyrodite Ag 8 GeS 6 = 4Ag 2 S•GeS 2 contains one-third isolated sulfur and two-thirds sulfur in GeS 4 tetrahedra, all connected by silver. 60 In glassy silver and thallium thiogermanates and thioarsenates, the isolated sulfur species appear far below the expected limits (M 2 S/GeS 2 = 2, and M 2 S/As 2 S 3 = 3) and in substantial concentrations (0.21 ≤ S iso /S tot ≤ 0.28) for x = 45−50 mol % M 2 S. 61 Likewise, the FPMD modeling of equimolar (Na 2 S) 0.5 (GeS 2 ) 0.5 glass 62 has shown the presence of 23.5% of isolated sulfur. On average, each isolated sulfur species is connected to two neighboring cations (M/S iso ≅ 2), and together, they form broad pathways going through the entire simulation box and ensuring high ionic conductivity (Figure S8).…”

Section: Resultsmentioning

confidence: 98%

Chemical and Structural Variety in Sodium Thioarsenate Glasses Studied by Neutron Diffraction and Supported by First-Principles Simulations

et al. 2020

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Sodium-conducting sulfide glasses are promising materials for the next generation of solid-state batteries. Deep insight into the glass structure is required to ensure a functional design and tailoring of vitreous alloys for energy applications. Using pulsed neutron diffraction supported by first-principles molecular dynamics, we show a structural diversity of Na2S–As2S3 sodium thioarsenate glasses, consisting of long corner-sharing (CS) pyramidal chains CS-(AsSS2/2) k , small As p S q rings (p + q ≤ 11), mixed corner- and edge-sharing oligomers, edge-sharing (ES) dimers ES-As2S4, and isolated (ISO) pyramids ISO-AsS3, entirely or partially connected by sodium species. Polysulfide S–S bridges and structural units with homopolar As–As bonds complete the glass structure, which is basically different from structural motifs predicted by the equilibrium phase diagram. In contrast to superionic silver and sodium sulfide glasses, characterized by a significant population of isolated sulfur species Siso (0.20 < Siso/Stot < 0.28), that is, sulfur connected to only mobile cations M+ with a usual M/Siso stoichiometry of 2, poorly conducting Na2S–As2S3 alloys exhibit a modest Siso fraction of 6.2%.

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“…Another possible complication includes a tetrahedral interconnected subnetwork in glassy GeTe 2 with intermediate-range ordering reminiscent of g-GeS 2 and g-GeSe 2 . However, metal doping, e.g., using silver or copper, leads to network depolymerization , and faster transformation processes in the amorphous state. Copper tellurogermanate Cu 2 GeTe 3 is an exciting example revealing new perspectives. , We should note that a significant population of triangular rings in Cu 2 GeTe 3 are also present in liquid GeTe 2 , Figure , revealing a resemblance in intermediate-range structures.…”

Section: Resultsmentioning

confidence: 99%

Bulk Glassy GeTe₂: A Missing Member of the Tetrahedral GeX₂ Family and a Precursor for the Next Generation of Phase-Change Materials

Tverjanovich¹,

Khomenko

Benmore

et al. 2021

Chem. Mater.

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Vitreous germanium disulfide GeS2 and diselenide GeSe2 belong to canonical chalcogenide glasses extensively studied over the past half century. Their high-temperature orthorhombic polymorphs are congruently melting compounds, and the tetrahedral crystal and glass structure is largely preserved in the melt. In contrast, the ditelluride counterpart is absent in the Ge–Te phase diagram, which shows only a single compound, monotelluride GeTe. Phase-change materials based on GeTe have become a technologically important class of solids, and their structure and properties are also widely studied. Surprisingly, very scarce information is available for alloys having GeTe2 stoichiometry. Using a fast quenching procedure in silica capillaries, high-energy X-ray diffraction, and Raman spectroscopy supported by first-principles simulations, we show that bulk glassy GeTe2 differs substantially from the lighter GeX2 members, revealing 46% of trigonal germanium, 31% of three-fold coordinated tellurium, and only 20% of edge-sharing tetrahedra or pyramids. The fraction of homopolar Ge–Ge bonds is low; however, the population of dominant Te–Te dimers and Te n oligomers, n ≤ 10, appears to be significant. The complex structural and chemical topology of g-GeTe2 is directly related to the thermodynamic metastability of germanium ditelluride, schematically represented by the following reaction: GeTe2 ⇄ GeTe + Te. Disproportionation is complete above liquidus in the temperature range of semiconductor–metal transition, and the dense metallic GeTe2 liquid, mostly consisting of five-fold coordinated Ge species, exhibits high fluidity, strong fragility (m = 99 ± 5), and presumably a fast structural transformation rate combined with low atomic mobility in the vicinity of the glass transition temperature, favorable for reliable long-term data retention in nonvolatile memories. The observed and predicted characteristic features make GeTe2 a promising precursor for the next generation of phase-change materials, especially coupled with additional metal doping, depolymerizing the tetrahedral interconnected glass network and accelerating (sub)nanosecond crystallization.

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Ionic Conductivity and Tracer Diffusion in Glassy Chalcogenides

Cited by 9 publications

References 0 publications

Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

Chemical and Structural Variety in Sodium Thioarsenate Glasses Studied by Neutron Diffraction and Supported by First-Principles Simulations

Bulk Glassy GeTe₂: A Missing Member of the Tetrahedral GeX₂ Family and a Precursor for the Next Generation of Phase-Change Materials

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Ionic Conductivity and Tracer Diffusion in Glassy Chalcogenides

Cited by 9 publications

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Mercury Thiogermanate Glasses HgS-GeS2: Vibrational, Macroscopic, and Electric Properties

Mercury Thiogermanate Glasses HgS-GeS2: Vibrational, Macroscopic, and Electric Properties

Chemical and Structural Variety in Sodium Thioarsenate Glasses Studied by Neutron Diffraction and Supported by First-Principles Simulations

Bulk Glassy GeTe2: A Missing Member of the Tetrahedral GeX2 Family and a Precursor for the Next Generation of Phase-Change Materials

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Product

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Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

Mercury Thiogermanate Glasses HgS-GeS₂: Vibrational, Macroscopic, and Electric Properties

Bulk Glassy GeTe₂: A Missing Member of the Tetrahedral GeX₂ Family and a Precursor for the Next Generation of Phase-Change Materials