A free energy landscape perspective on the nature of collective diffusion in amorphous solids

Wang, Yun-Jiang; Du, Jun‐Ping; Shinzato, Shuhei; Dai, Lan-Hong; Ogata, Shigenobu

doi:10.1016/j.actamat.2018.07.029

Cited by 39 publications

(18 citation statements)

References 76 publications

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“…For the 50 % site-inverted systems we observe a range of string lengths, with P (n) following an approximate geometric distribution. This mirrors the behaviour observed in supercooled glassy liquids [97] where string-like diffusion is often associated with dynamic heterogeneity [56,[99][100][101], whereby spatially cor- related subsets of particles exhibit much faster dynamics than the system average. A geometric distribution of string lengths is consistent with a mechanistic model consisting of string "initiation", followed by string "propagation" with the probability of a string increasing in length from N particles to N + 1 particles is independent of N .…”

Section: S-lisupporting

confidence: 68%

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

Morgan

2021

Preprint

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The rational development of fast–ion-conducting solid electrolytes for all-solid-state lithium-ion batteries requires understanding the key structural and chemical principles that give some materials their exceptional ionic conductivities. For the lithium argyrodites Li6PS5X (X = Cl,Br,I), the choice of the halide, X, strongly affects the ionic conductivity, with room-temperature ionic conductivities for X = {Cl, Br} ×103 higher than for X = I. This variation has been attributed to differing degrees of S/X anion disorder. For X = {Cl, Br} the S/X anions are substitutionally disordered, while for X = I the anion sublattice is fully ordered. To better understand the role of substitutional anion disorder in enabling fast lithium-ion transport, we have performed a first-principles molecular dynamics study of Li6PS5I and Li6PS5Cl, with varying amounts of S/X anion-site disorder. Considering the S/X substructure as a tetrahedrally close-packed lattice, we identify three partially occupied lithium sites that form a contiguous three-dimensional network of face-sharing tetrahedra. The active lithium-ion diffusion pathways within this network, however, depend on the S/X anion configuration. For anion-disordered systems, the active site–site pathways give a percolating three-dimensional diffusion network; whereas for anion-ordered systems, critical site–site pathways are inactive, giving a disconnected diffusion network with lithium motion restricted to local orbits around S positions. Analysis of the lithium substructure and dynamics in terms of the lithium coordination around each sulfur site shows a mechanistic link between substitutional anion disorder and lithium disorder, which enables fast lithium diffusion. In anion-ordered systems the Li-ions are pseudo-ordered, with preferential 6-fold coordination of sulfur sites. Long-ranged lithium diffusion disrupts this SLi6 pseudo-ordering, and is therefore disfavoured. In anion-disordered systems, a uniform 6-fold S–Li coordination is frustrated due to Li–Li Coulombic repulsion. Lithium positions become disordered, giving a range of S–Li coordination environments. Long-ranged Li diffusion is now possible with no net change in S–Li coordination numbers. This gives rise to superionic lithium transport in the anion-disordered systems, which is effected by a concerted string-like diffusion mechanism.

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Section: S-lisupporting

confidence: 68%

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

Morgan

2021

Preprint

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show abstract

“…For the 50% site-inverted systems, we observe a range of string lengths, with P ( n ) following an approximate geometric distribution. This mirrors the behavior observed in supercooled glassy liquids where string-like diffusion is often associated with dynamic heterogeneity , ,− whereby spatially correlated subsets of particles exhibit much faster dynamics than the system average. A geometric distribution of string lengths is consistent with a mechanistic model consisting of string “initiation”, followed by string “propagation” with the probability of a string increasing in length from N particles to N + 1 particles is independent of N .…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li₆PS₅X Argyrodites

Morgan

2021

Chem. Mater.

112

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The rational development of fast-ion-conducting solid electrolytes for all-solid-state lithium-ion batteries requires understanding the key structural and chemical principles that give some materials their exceptional ionic conductivities. For the lithium argyrodites Li 6 PS 5 X (X = Cl, Br, or I), the choice of the halide, X, strongly affects the ionic conductivity, giving room-temperature ionic conductivities for X = {Cl,Br} that are ×10 3 higher than for X = I. This variation has been attributed to differing degrees of S/X anion disorder. For X = {Cl,Br}, the S/X anions are substitutionally disordered, while for X = I, the anion substructure is fully ordered. To better understand the role of substitutional anion disorder in enabling fast lithium-ion transport, we have performed a first-principles molecular dynamics study of Li 6 PS 5 I and Li 6 PS 5 Cl with varying amounts of S/X anion-site disorder. By considering the S/X anions as a tetrahedrally close-packed substructure, we identify three partially occupied lithium sites that define a contiguous three-dimensional network of face-sharing tetrahedra. The active lithium-ion diffusion pathways within this network are found to depend on the S/X anion configuration. For anion-disordered systems, the active site–site pathways give a percolating three-dimensional diffusion network; whereas for anion-ordered systems, critical site–site pathways are inactive, giving a disconnected diffusion network with lithium motion restricted to local orbits around S positions. Analysis of the lithium substructure and dynamics in terms of the lithium coordination around each sulfur site highlights a mechanistic link between substitutional anion disorder and lithium disorder. In anion-ordered systems, the lithium ions are pseudo-ordered, with preferential 6-fold coordination of sulfur sites. Long-ranged lithium diffusion would disrupt this SLi 6 pseudo-ordering, and is, therefore, disfavored. In anion-disordered systems, the pseudo-ordered 6-fold S–Li coordination is frustrated because of Li–Li Coulombic repulsion. Lithium positions become disordered, giving a range of S–Li coordination environments. Long-ranged lithium diffusion is now possible with no net change in S–Li coordination numbers. This gives rise to superionic lithium transport in the anion-disordered systems, effected by a concerted string-like diffusion mechanism.

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“…On the increasing temperature, the thermal vibration energy becomes larger than the energy barrier, and it can lead to thermal activations for atom rearrangement in MGs [ 60 ]. When the annealing temperature reaches T g , the large size atomic diffusion notably promotes the atomic transport [ 61 ]. Some fast degrees of freedom frozen in the deep glassy state are reactivated.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Structural Heterogeneity and Corrosion Performance of the Annealed Fe-Based Metallic Glasses

et al. 2021

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This study investigated the structural heterogeneity, mechanical property, electrochemical behavior, and passive film characteristics of Fe–Cr–Mo–W–C–B–Y metallic glasses (MGs), which were modified through annealing at different temperatures. Results showed that annealing MGs below the glass transition temperature enhanced corrosion resistance in HCl solution owing to a highly protective passive film formed, originating from the decreased free volume and the shrinkage of the first coordination shell, which was found by pair distribution function analysis. In contrast, the enlarged first coordination shell and nanoscale crystal-like clusters were identified for MGs annealed in the supercooled liquid region, which led to a destabilized passive film and thereby deteriorated corrosion resistance. This finding reveals the crucial role of structural heterogeneity in tuning the corrosion performance of MGs.

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A free energy landscape perspective on the nature of collective diffusion in amorphous solids

Cited by 39 publications

References 76 publications

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li₆PS₅X Argyrodites

Investigation of the Structural Heterogeneity and Corrosion Performance of the Annealed Fe-Based Metallic Glasses

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