Structural Origin of the Thermal and Diffusion Behaviors of Lithium Aluminosilicate Crystal Polymorphs and Glasses

Abstract

Lithium aluminosilicate polymorphs a-LiAlSi 2 O 6 , b-LiAlSi 2 O 6 , and the LiAlSi 2 O 6 glass have been studied comparatively using classical molecular dynamics (MD) simulations with an aim to better understand the structural origin of the different thermomechanical behaviors and lithium ion diffusion properties. The melting behaviors and structural evolution were investigated for the three phases using MD simulations. The structural features of the three simulated samples were analyzed using coordination number, pair and bond angle distributions. The results showed that b-LiAlSi 2 O 6 and the LiAlSi 2 O 6 glass had similar melting behavior, had more random short-range atomic structures, and lower densities as compared to the a-LiAlSi 2 O 6 phase, which has a more ordered and compact structure. The lithium ion diffusion behavior in a-LiAlSi 2 O 6 , b-LiAlSi 2 O 6 , and LiAlSi 2 O 6 glass and their melts are determined and compared by calculating the mean square displacements. It was found that at high temperatures, the melts of a-LiAlSi 2 O 6 , b-LiAlSi 2 O 6 , and LiAlSi 2 O 6 glass had similar diffusion properties. While at low temperatures, a-LiAlSi 2 O 6 had the lowest diffusion coefficient and highest diffusion energy barrier due to its more close-packed structure and lacking of defects to facilitate lithium ion diffusion. Both the b-LiAlSi 2 O 6 and glass show high ionic conductivity even at low temperatures. This originates from their lower density and thus relatively open structures, but slightly different diffusion mechanisms. Lithium ion diffusion in b-LiAlSi 2 O 6 is through the large available interstitial sites while that in the glass is through vacancies due to high free volume. The glass phase had slightly lower lithium ion diffusion energy barrier and higher lithium ion diffusion coefficients as compared to the b-LiAlSi 2 O 6 phase, indicating the glass phase can achieve high ionic diffusion and, in some cases, even higher than the crystalline phases with similar densities and short-range structures.

Local ordering and interfacial structure between spinel crystal and aluminosilicate glasses from molecular dynamics simulations

“…These data show the adopted empirical potential can describe the complex oxide system especially the structures very well. In addition, this set of potential has been applied to several aluminosilicate glass systems and were shown to be capable to capture the complex glass structure, mechanical and thermal properties.…”

“…In addition, as the Al/Na ratio increases, the five coordinated Al increases while four coordinated Al decreases. Later, Ren et al reported the similar behavior of Al for lithium aluminosilicate glasses. However, different from previous studies, the simulated glass in this work contains two glass modifiers, Na and Mg.…”

“…Due to its ability to investigate atomic level structural details and dynamic behaviors, molecular dynamics (MD) computer simulations have been used extensively to describe the structures and properties of oxide glasses . MD has also been used to study crystal/crystal and crystal/amorphous interfaces.…”

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

“…MSD plot can be classified into three regions: a ballistic region for short time (proportional to t 2 ), a plateau region and a diffusion region for long time (proportional to t). 28,51,59 The last diffusion region (80-100 ps) was used to calculate the self-diffusion coefficients based on Einstein's equation. In Fig.…”

Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) ‐ eucryptite (LiAlSiO4) join

“…Many studies have been conducted over the years seeking to identify possible causal relationships between glass structure and resulting crystallization tendencies, particularly nucleation, as has been recently reviewed by Zanotto et al These authors argue that the available data suggest that tendency for homogeneous nucleation of crystallization is driven by glass‐crystal similarities in network modifier cation positions in short‐range order (e.g., coordination number differences) and intermediate‐range order (e.g., network former/modifier correlations, modifier distance distributions) but not medium‐range order (e.g., network ring‐size statistics). Meanwhile, molecular dynamics studies on spodumene (LiAlSi 2 O 6 ) have shown that the reason for the ubiquitous crystallization of β‐spodumene from the melt, instead of naturally occurring α‐spodumene, is likely due to the similarities in Al and Li coordination numbers as well as bond angle similarities in the glass and β‐spodumene . To our knowledge, no literature exists demonstrating the influence of a mixed‐alkali effect on the crystallization behavior of aluminosilicate glasses.…”