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Title: First-principles study of the structural and dynamic properties of the liquid and amorphous Li–Si alloys

We have performed density functional theory calculations and ab initio molecular dynamics to investigate the structures and dynamic properties of the liquid and amorphous Li{sub x}Si alloys over a range of composition from x = 1.0 − 4.8. Our results show that Si atoms can form a variety of covalently bonded polyanions with diverse local bonding structures in the liquid alloys. Like in c-LiSi, Si atoms can form a continuous bond network in liquid Li{sub 1.0}Si at 1050 K, while it gradually disintegrates into many smaller Si polyanions as the Li content increases in the alloys. The average sizes of Si polyanions in these liquid alloys were found to be relatively larger than those in their crystalline counterparts, which can even persist in the highly lithiated Li{sub 4.81}Si alloy at 1500 K. Our results also show that amorphous Li{sub x}Si alloys have similar local bonding structures but a largely increased short-range order as compared to their liquid counterparts. The differences between the average coordination number of each atomic pair in amorphous solids and that in the liquids are less than 1.1. Furthermore, our calculations reveal that Li and Si atoms can exhibit very distinct dynamic behaviors in the liquids andmore » their diffusivities appear to be largely dependent on the chemical composition of the alloys. The diffusivity of Li was found to increase with the Li content in the alloys primarily because of the reduced interactions between Li and Si atoms, while the Si diffusivity also increases due to the gradual disintegration of the strongly interconnected Si bond network. The diffusivity of Li in amorphous Li{sub x}Si was predicted to lie in the range between 10{sup −7} and 10{sup −9} cm{sup 2}/s at 300 K, which is more than 20-fold larger than that of Si over the composition range considered. Our calculations further show that the diffusivities of both Li and Si can increase by two orders of magnitude as x increases from 1.0 to 3.57 in amorphous Li{sub x}Si, indicating a more profound dependence on the alloy composition than those in the liquid state.« less
Authors:
;  [1] ;  [2]
  1. Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China)
  2. National Center for High-Performance Computing, Tainan 74147, Taiwan (China)
Publication Date:
OSTI Identifier:
22493669
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 144; Journal Issue: 3; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMORPHOUS STATE; ATOMS; CHEMICAL BONDS; CHEMICAL COMPOSITION; COMPARATIVE EVALUATIONS; CONCENTRATION RATIO; COORDINATION NUMBER; COVALENCE; DENSITY FUNCTIONAL METHOD; LIQUIDS; LITHIUM ALLOYS; MOLECULAR DYNAMICS METHOD; SILICON ALLOYS; SOLIDS; TEMPERATURE DEPENDENCE