First-Principles Molecular Dynamics Simulation and Conductivity Measurements of a Molten xLi₂O–(1 – x)B₂O₃ System

Abstract

The electronic properties and atomic structure of a molten xLi2O-(1 - x)B2O3 system were investigated by measuring conductivity and using first-principles molecular dynamics (MD) simulations. The conductivities obtained were converted to a Li self-diffusion coefficient Dσ, using the Nernst-Einstein equation to assess charge transfer mechanisms. Dσ was compared with a Li self-diffusion coefficient, DNMR, which we measured in a previous study using high-temperature pulsed field gradient NMR. The DNMR/Dσ of xLi2O-(1 - x)B2O3 (0.2 ≤ x ≤ 0.5) at 1250 K ranged from 2.5 to 3.2, following the same trend as room temperature ionic liquids. First-principles MD simulations were performed using our own finite element density functional theory code, FEMTECK (finite element method-based total energy calculation) for molten xLi2O-(1 - x)B2O3 systems at 1250 K. We found that the O-B-O angle distribution functions were characterized by a peak at approximately 120°. Although the electron number from the electronic radial distribution function was arbitrary with regard to the cutoff distance, the net Li charge calculated from the integrated electron number surrounding Li was approximately 0.9 at 0.085 nm. The mean square displacement (MSD) of Li as a function of time was evaluated from the atomic configuration. Li self-diffusion coefficients calculated from the MSD were in better agreement with experimental results than they were using classical MD.

Consequences of sp2–sp3 boron isomerization in supercooled liquid borates

“…By construction, B 2 O 3 has a constant n BO of 3, whereas that for LiBO 2 rises continuously from $3.1 above the melting point to $3.4 below T g . Both values are in excellent agreement with 11 B NMR 10,15,16 and non-resonant inelastic x-ray scattering 17 determinations for the glass and with both ab-initio 11 and classical 18 molecular dynamics models for the equilibrium liquid. Our time-resolved, diffraction-based data fill the gap between the ambient temperature measurements and the equilibrium liquid simulations.…”

“…Our experimental study focuses on lithium metaborate, LiBO 2 , which has a high fragility index (m % 77) 7,8 and lithium ion conductivity. [9][10][11] Accurate measurements of the sp 3 isomer fraction, N 4 (T), as a function of temperature, T, allow parameterization of a simple thermodynamic model based on the Li þ cation content per boron, J ¼ Li 2 O/B 2 O 3 , controlling the abundance of negatively charged trigonal sp 2 (BØ 2 O À ) and tetrahedral sp 3 (BØ 4…”

“…Comparison is made to literature data. 10,11,[15][16][17][18] Glass transition and melting temperatures are indicated by arrows. The blue curve is the result of van't Hoff analysis (Fig.…”

Borate melt structure: Temperature‐dependent B–O bond lengths and coordination numbers from high‐energy X‐ray diffraction

“…Ablett, G. Monaco, unpublished data). Theoretical investigations include thermodynamic, statistical mechanical and both classical and first principles molecular dynamics modeling. The overall consensus is that reactions like that illustrated in Figure tend to the right with increasing temperature, such that Δ n BO /Δ T is negative, and typically smaller in magnitude than 1 × 10 −3 K −1 .…”

Insights from ab initio molecular dynamics simulations for a multicomponent oxide glass

“…The computational costs of Fourier transforms are considerable, therefore, ab initio calculation using finite‐element basis functions in real space can be used as an alternative approach to express localized wave functions for amorphous materials and reduce computational costs without the need for Fourier transforms. Application of this original approach has been successful for relatively large atomic systems, including oxide glass and polymers . A simple question is whether the present situation for AIMD has the ability to reproduce atomic structures consistent with the most advanced diffraction and NMR data.…”