1
|
Lee SC, Z Y. Unusual dynamics of tetrahedral liquids caused by the competition between dynamic heterogeneity and structural heterogeneity. J Chem Phys 2024; 161:044502. [PMID: 39037136 DOI: 10.1063/5.0215370] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2024] [Accepted: 07/02/2024] [Indexed: 07/23/2024] Open
Abstract
Tetrahedral liquids exhibit intriguing thermodynamic and transport properties because of the various ways tetrahedra can be packed and connected. Recently, an unusual temperature dependence of the stretching exponent β in a model tetrahedral liquid ZnCl2 from Tm + 85 K to Tm + 35 K has been reported using neutron-spin echo spectroscopy. This discovery stands in sharp contrast to other glass-forming liquids. In this study, we conducted neural network force field driven molecular dynamic simulations of ZnCl2. We found a non-monotonic temperature dependence of β from liquid to supercooled liquid temperatures. Further structural decomposition and dynamic analysis suggest that this unusual dynamic behavior is a result of the competition between the decrease in the diversity of tetrahedra motifs (structural heterogeneity) and the increase in glassy dynamic heterogeneity. This result may contribute to new understandings of the structural relaxation of other network liquids.
Collapse
Affiliation(s)
- Shao-Chun Lee
- Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Y Z
- Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Department of Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, Michigan 48109, USA
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| |
Collapse
|
2
|
Liu Q, Li X. Molten salt synthesis of porous graphene-like carbons as peroxydisulfate catalyst for the efficient removal of rhodamine B dye. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2024; 31:43249-43261. [PMID: 38898350 DOI: 10.1007/s11356-024-33951-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2024] [Accepted: 06/05/2024] [Indexed: 06/21/2024]
Abstract
Carbon materials have been receiving considerable attention as effective green catalysts for peroxydisulfate (PDS) activation to degrade organic pollutants. Herein, the porous graphene-like carbons (PGCs) were synthesized by pyrolyzing a nitrogen-rich biomass (peanut shell, PS) in the eutectic mixture of FeCl3 and ZnCl2. The results suggested that involvement of molten salts attributed the biochar the amazing properties such as high specific surface area (SBET = 2529.4 m2 g-1), abundant structural defects, high nitrogen content (6.5%), and oxygen-containing functional groups on its surface. Especially when pyrolyzed at activation temperature of 800 °C, mass ratio of 1:3:15 (PS:ZnCl2:FeCl3), and activation time of 2 h, the optimized PGCs-op exhibited outstanding performance in the catalytic degradation of rhodamine B (RhB). Almost all of RhB (99.02%) was removed in 40 min and basically not influenced by initial pH in the range of 3.00 to 9.98. Although the RhB degradation was influenced by anions (Cl-, HCO3-, HPO42-), the inhibition would be significantly alleviated within 120 min unless these substances were high in concentration. Furthermore, the quenching tests revealed that the reactive species were involved in RhB degradation in the sequence of 1O2 > O2∙- > SO4∙- > ∙OH, among which singlet oxygen played a crucial role. Combined with characterization analysis, a possible mechanism of RhB degradation in PGCs-op/PDS system was proposed. Overall, this study provided a promising metal-free catalyst for the removal of organic pollutants while achieving reutilization of the waste biomass.
Collapse
Affiliation(s)
- Qiong Liu
- School of Environmental Engineering and Chemistry, Luoyang Institute of Science and Technology, No. 90 of Wangcheng Road, Luoyang, 471000, China.
| | - Xinghang Li
- School of Environmental Engineering and Chemistry, Luoyang Institute of Science and Technology, No. 90 of Wangcheng Road, Luoyang, 471000, China
| |
Collapse
|
3
|
Nguyen HH, Bryantsev VS, Margulis CJ. Are High-Temperature Molten Salts Reactive with Excess Electrons? Case of ZnCl 2. J Phys Chem B 2023; 127:9155-9164. [PMID: 37753927 PMCID: PMC10614199 DOI: 10.1021/acs.jpcb.3c04210] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 08/21/2023] [Indexed: 09/28/2023]
Abstract
New and exciting frontiers for the generation of safe and renewable energy have brought attention to molten inorganic salts of fluorides and chlorides. This is because high-temperature molten salts can act both as coolants and liquid fuel in next-generation nuclear reactors. Whereas research from a few decades ago suggests that salts are mostly unreactive to radiation, recent experiments hint at the fact that electrons generated in such extreme environments can react with the melt and form new species including nanoparticles. Our study probes the fate of an excess electron in molten ZnCl2 using first-principles molecular dynamics calculations. We find that on the time scale accessible to our study, an excess electron can be found in one of three states; the lowest-energy state can be characterized as a covalent Zn2Cl5•2- radical ion, the other two states are a solvated Zn•+ species (ZnCl3•2-) and a more delocalized species that still has some ZnCl3•2- character. Since for each of these, the singly occupied molecular orbital (SOMO) where the excess charge resides has a distinct and well-separated energy, the different species can in principle be characterized by their own electronic spectra. The study also sheds light onto what is commonly understood as the spectrum of a transient radical species which can be from the SOMO onto higher energy states or from the melt to pair with the excess electron leaving a hole in the liquid.
Collapse
Affiliation(s)
- Hung H. Nguyen
- Department
of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
| | - Vyacheslav S. Bryantsev
- Chemical
Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Claudio J. Margulis
- Department
of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
| |
Collapse
|
4
|
Luo P, Zhai Y, Falus P, García Sakai V, Hartl M, Kofu M, Nakajima K, Faraone A, Z Y. Q-dependent collective relaxation dynamics of glass-forming liquid Ca 0.4K 0.6(NO 3) 1.4 investigated by wide-angle neutron spin-echo. Nat Commun 2022; 13:2092. [PMID: 35440658 PMCID: PMC9018732 DOI: 10.1038/s41467-022-29778-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Accepted: 03/29/2022] [Indexed: 11/30/2022] Open
Abstract
The relaxation behavior of glass formers exhibits spatial heterogeneity and dramatically changes upon cooling towards the glass transition. However, the underlying mechanisms of the dynamics at different microscopic length scales are not fully understood. Employing the recently developed wide-angle neutron spin-echo spectroscopy technique, we measured the Q-dependent coherent intermediate scattering function of a prototypical ionic glass former Ca0.4K0.6(NO3)1.4, in the highly viscous liquid state. In contrast to the structure modulated dynamics for Q < 2.4 Å−1, i.e., at and below the structure factor main peak, for Q > 2.4 Å−1, beyond the first minimum above the structure factor main peak, the stretching exponent exhibits no temperature dependence and concomitantly the relaxation time shows smaller deviations from Arrhenius behavior. This finding indicates a change in the dominant relaxation mechanisms around a characteristic length of 2π/(2.4 Å−1) ≈ 2.6 Å, below which the relaxation process exhibits a temperature independent distribution and more Arrhenius-like behavior. Length scale dependence is important for understanding the collective relaxation dynamics in glass-forming liquids. Here, the authors find in liquid Ca0.4K0.6(NO3)1.4 a change in the dominant relaxation mechanisms around 2.6 Å, below which the relaxation process exhibits a temperature independent distribution and more Arrhenius-like behavior.
Collapse
Affiliation(s)
- Peng Luo
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Yanqin Zhai
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.,Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Peter Falus
- Institut Laue-Langevin (ILL), 38042, Grenoble, France
| | - Victoria García Sakai
- ISIS Neutron and Muon Facility, Rutherford Appleton Laboratory, Science & Technology Facilities Council, Didcot, OX11 0QX, UK
| | - Monika Hartl
- European Spallation Source, SE-221 00, Lund, Sweden
| | - Maiko Kofu
- J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Kenji Nakajima
- J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Antonio Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD, 20899-1070, USA.
| | - Y Z
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA. .,Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA. .,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
| |
Collapse
|
5
|
Hultmark S, Cravcenco A, Kushwaha K, Mallick S, Erhart P, Börjesson K, Müller C. Vitrification of octonary perylene mixtures with ultralow fragility. SCIENCE ADVANCES 2021; 7:7/29/eabi4659. [PMID: 34272241 PMCID: PMC8284888 DOI: 10.1126/sciadv.abi4659] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 06/02/2021] [Indexed: 05/08/2023]
Abstract
Strong glass formers with a low fragility are highly sought-after because of the technological importance of vitrification. In the case of organic molecules and polymers, the lowest fragility values have been reported for single-component materials. Here, we establish that mixing of organic molecules can result in a marked reduction in fragility. Individual bay-substituted perylene derivatives display a high fragility of more than 70. Instead, slowly cooled perylene mixtures with more than three components undergo a liquid-liquid transition and turn into a strong glass former. Octonary perylene mixtures display a fragility of 13 ± 2, which not only is a record low value for organic molecules but also lies below values reported for the strongest known inorganic glass formers. Our work opens an avenue for the design of ultrastrong organic glass formers, which can be anticipated to find use in pharmaceutical science and organic electronics.
Collapse
Affiliation(s)
- Sandra Hultmark
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Alex Cravcenco
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296 Göteborg, Sweden
| | - Khushbu Kushwaha
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296 Göteborg, Sweden
| | - Suman Mallick
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296 Göteborg, Sweden
| | - Paul Erhart
- Department of Physics, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Karl Börjesson
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296 Göteborg, Sweden
| | - Christian Müller
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden.
| |
Collapse
|
6
|
King EA, Sen S, Takeda W, Boussard-Pledel C, Bureau B, Guin JP, Lucas P. Extended aging of Ge-Se glasses below the glass transition temperature. J Chem Phys 2021; 154:164502. [PMID: 33940843 DOI: 10.1063/5.0050474] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Germanium selenide glasses of compositions spanning the whole glass-formation range are aged at room temperature for up to 20 years. A prominent enthalpy relaxation process is observed in all glasses, and its structural origin is analyzed by Raman spectroscopy. The structural relaxation is manifested in the Raman spectra as a decrease in the ratio of edge- to corner-sharing GeSe4/2 tetrahedral units. This structural evolution can be explained in terms of configurational entropy and density changes. Changes in Raman features and enthalpy follow an identical stretched exponential relaxation function characteristic of aging in glasses. The compositional dependence of enthalpy relaxation after 20 years is in agreement with kinetic considerations based on the glass transition temperature of each glass. The relaxation behavior and heat capacity curves are consistent with standard glass relaxation models for all compositions. These results indicate that the non-reversing enthalpy obtained by modulated differential scanning calorimetry (MDSC), which suggests the existence of non-aging glasses, is not a reliable measure of the ability of a glass to relax. Instead, it is suggested that an interpretation of MDSC data in terms of complex heat capacity provides a more complete and reliable assessment of the relaxation properties of glasses.
Collapse
Affiliation(s)
- Ellyn A King
- Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721, USA
| | - Sabyasachi Sen
- Department of Materials Science and Engineering, University of California, Davis, California 95616, USA
| | - Wataru Takeda
- Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721, USA
| | - Catherine Boussard-Pledel
- Univ. Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-35000 Rennes, France
| | - Bruno Bureau
- Univ. Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-35000 Rennes, France
| | - Jean-Pierre Guin
- Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, Rennes, France
| | - Pierre Lucas
- Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721, USA
| |
Collapse
|
7
|
Luo P, Zhai Y, Leao JB, Kofu M, Nakajima K, Faraone A, Z Y. Neutron Spin-Echo Studies of the Structural Relaxation of Network Liquid ZnCl 2 at the Structure Factor Primary Peak and Prepeak. J Phys Chem Lett 2021; 12:392-398. [PMID: 33356292 DOI: 10.1021/acs.jpclett.0c03146] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Using neutron spin-echo spectroscopy, we studied the microscopic structural relaxation of a prototypical network ionic liquid ZnCl2 at the structure factor primary peak and prepeak. The results show that the relaxation at the primary peak is faster than the prepeak and that the activation energy is ∼33% higher. A stretched exponential relaxation is observed even at temperatures well-above the melting point Tm. Surprisingly, the stretching exponent shows a rapid increase upon cooling, especially at the primary peak, where it changes from a stretched exponential to a simple exponential on approaching the Tm. These results suggest that the appearance of glassy dynamics typical of the supercooled state even in the equilibrium liquid state of ZnCl2 as well as the difference of activation energy at the two investigated length scales are related to the formation of a network structure on cooling.
Collapse
Affiliation(s)
- Peng Luo
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Yanqin Zhai
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Juscelino B Leao
- National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-1070, United States
| | - Maiko Kofu
- J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Kenji Nakajima
- J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
| | - Antonio Faraone
- National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-1070, United States
| | - Y Z
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| |
Collapse
|
8
|
Ryu CW, Egami T. Origin of liquid fragility. Phys Rev E 2020; 102:042615. [PMID: 33212574 DOI: 10.1103/physreve.102.042615] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 10/12/2020] [Indexed: 11/07/2022]
Abstract
Liquid fragility characterizes how steeply the viscosity of a glass-forming liquid decreases with increasing temperature above the glass transition. It is one of the most fundamental properties of a liquid, with high importance for science and application. Yet, its origin is unclear. Here we show that it is directly related to the structural coherence of the medium-range order (MRO) in liquid defined by the decay of the pair-distribution function with distance. The MRO can also be evaluated from the first peak of the structure function determined by x-ray or neutron diffraction, and it is a measure of the cooperativity of atomic motion in a diffusive event in supercooled liquids. These findings shed light on the mechanism of atomic transport in supercooled liquids.
Collapse
Affiliation(s)
- Chae Woo Ryu
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Takeshi Egami
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.,Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.,Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
| |
Collapse
|
9
|
Liang W, Lu G, Yu J. Composition-dependent microstructure evolution in liquid MgCl2-KCl: A first-principles molecular dynamics study. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113131] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
10
|
Liang W, Wu J, Ni H, Lu G, Yu J. First-principles molecular dynamics simulations on the local structure and thermo-kinetic properties of molten magnesium chloride. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2019.112063] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
11
|
Peng SX, Cheng Y, Pries J, Wei S, Yu HB, Wuttig M. Uncovering β-relaxations in amorphous phase-change materials. SCIENCE ADVANCES 2020; 6:eaay6726. [PMID: 31950085 PMCID: PMC6954054 DOI: 10.1126/sciadv.aay6726] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 11/11/2019] [Indexed: 05/23/2023]
Abstract
Relaxation processes are decisive for many physical properties of amorphous materials. For amorphous phase-change materials (PCMs) used in nonvolatile memories, relaxation processes are, however, difficult to characterize because of the lack of bulk samples. Here, instead of bulk samples, we use powder mechanical spectroscopy for powder samples to detect the prominent excess wings-a characteristic feature of β-relaxations-in a series of amorphous PCMs at temperatures below glass transitions. By contrast, β-relaxations are vanishingly small in amorphous chalcogenides of similar composition, which lack the characteristic features of PCMs. This conclusion is corroborated upon crossing the border from PCMs to non-PCMs, where β-relaxations drop substantially. Such a distinction implies that amorphous PCMs belong to a special kind of covalent glasses whose locally fast atomic motions are preserved even below the glass transitions. These findings suggest a correlation between β-relaxation and crystallization kinetics of PCMs, which have technological implications for phase-change memory functionalities.
Collapse
Affiliation(s)
- Si-Xu Peng
- Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
| | - Yudong Cheng
- I. Institute of Physics (IA), RWTH Aachen University, 52074 Aachen, Germany
| | - Julian Pries
- I. Institute of Physics (IA), RWTH Aachen University, 52074 Aachen, Germany
| | - Shuai Wei
- I. Institute of Physics (IA), RWTH Aachen University, 52074 Aachen, Germany
| | - Hai-Bin Yu
- Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
| | - Matthias Wuttig
- I. Institute of Physics (IA), RWTH Aachen University, 52074 Aachen, Germany
- JARA-Institute Green IT (PGI-10), FZ-Jülich, 52428 Jülich, Germany
| |
Collapse
|
12
|
Yuan B, Aitken B, Sen S. Is the λ-transition in liquid sulfur a fragile-to-strong transition? J Chem Phys 2019; 151:041105. [PMID: 31370520 DOI: 10.1063/1.5110177] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The abrupt and large increase in the viscosity of liquid sulfur above the λ-transition temperature Tλ corresponds to a reversible structural transformation in the form of a ring-to-chain polymerization reaction. The mechanistic connection between this structural transformation and viscosity is investigated by studying the compositional dependence of the shear relaxation behavior of supercooled SxSe100-x liquids as their structural evolution mimics that of liquid sulfur across the λ-transition. The results of steady and oscillatory shear parallel-plate rheometry indicate that the viscosity of these liquids is controlled by the S/Se-S/Se bond scission/renewal dynamics and the time scale of these dynamics rapidly increases as the relative concentrations of rings and chains in the structure become comparable. The coexistence of these two types of topological units in these liquids lowers the conformational entropy of the chain elements due to a steric hindrance from the ring elements, resulting in a rapid drop in the fragility as S is added to Se. The same topological effect resulting from the ring-to-chain transformation in liquid S renders the highly fragile molecular liquid below Tλ, a strong polymerized liquid above Tλ. Therefore, it is argued that the λ-transition of liquid S corresponds to a fragile-to-strong liquid-liquid transition.
Collapse
Affiliation(s)
- Bing Yuan
- Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA
| | - Bruce Aitken
- Science and Technology Division, Corning, Inc., Corning, New York 14831, USA
| | - Sabyasachi Sen
- Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA
| |
Collapse
|
13
|
Aravindakshan NP, Johnson KE, East ALL. The origin of the conductivity maximum in molten salts. III. Zinc halides. J Chem Phys 2019; 151:034507. [PMID: 31325937 DOI: 10.1063/1.5109138] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
In a continuing effort to master the reasons for conductivity maxima vs temperature in semicovalent molten halides, the structure and some transport properties of molten zinc halide are examined with ab initio molecular dynamics. Molten zinc halides are a special class of molten salts, being extremely viscous near their melting point (with a glassy state below it) and low electrical conductivity, and since they are also known (ZnI2) or predicted (ZnBr2 and ZnCl2) to exhibit conductivity maxima, they would be useful additional cases to probe, in case the reasons for their maxima are unique. Strong attractive forces in ZnX2 result in tight tetrahedral coordination, and the known mixture of edge-sharing vs corner-sharing ZnX4 tetrahedra is observed. In the series zinc chloride → bromide → iodide, (i) the ratio of edge-sharing vs corner-sharing tetrahedra increases, (ii) the diffusion coefficient of Zn2+ increases, and (iii) the diffusion coefficient of the anion stays roughly constant. A discussion of conductivity, with focus on the Walden product W = ηΛe, is presented. With predicted Haven ratios of 1-15 when heated toward their conductivity maxima, the physical chemistry behind molten zinc halide conductivity does not appear to be fundamentally different from other semicovalent molten halides.
Collapse
Affiliation(s)
- Nikhil P Aravindakshan
- Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
| | - Keith E Johnson
- Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
| | - Allan L L East
- Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
| |
Collapse
|
14
|
Marple MAT, Yong V, Sen S. Fragility and aging behavior of Si xSe 1-x glasses and liquids. J Chem Phys 2019; 150:044506. [PMID: 30709249 DOI: 10.1063/1.5080225] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The composition dependence of the fragility of SixSe1-x liquids with 0.05 ≤ x ≤ 0.33 is determined using the calorimetric method and is found to be rather similar to that characteristic of their Ge analogues. In addition, the nature and the time scale of the structural relaxation of the Si25Se75 glass during aging at 40 K below Tg are measured using Raman spectroscopy. The structural relaxation in this glass, which belongs to the so-called intermediate phase, involves progressive conversion of the doubly edge-shared SiSe4/2 tetrahedra E2 into singly edge-shared E1 and corner-shared E0 tetrahedra upon lowering of temperature. This tetrahedral speciation can be expressed in the form of the reaction 2 E2 → E0 + E1. The time scale of this tetrahedral conversion reaction corresponds well with that of shear relaxation. This result is inconsistent with the claim made previously in the literature that intermediate phase compositions do not undergo aging. Moreover, when taken together, the fragility and the structural relaxation results suggest that the constraint counting scheme typically adopted in the literature for edge- vs. corner-shared tetrahedra in chalcogenide networks may need to be revised. A rigid-polytope based constraint counting approach is shown to be more consistent with the experimental results.
Collapse
Affiliation(s)
- Maxwell A T Marple
- Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA
| | - Vuthtyra Yong
- Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA
| | - Sabyasachi Sen
- Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA
| |
Collapse
|