Phonons and lithium diffusion in LiAlO2

Abstract

We report on investigations of phonons and lithium diffusion in LiAlO2 based on inelastic neutron scattering (INS) measurements of the phonon density of states (DOS) in γ-LiAlO2 from 473 K to 1073 K, complemented with ab-initio molecular dynamics (AIMD) simulations. We find that phonon modes related to Li vibrations broaden on warming as reflected in the measured phonon DOS and reproduced in simulations. Further, the AIMD simulations probe the nature of lithium diffusion in the perfect crystalline phase (γ-LiAlO2), as well as in a structure with lithium vacancies and a related amorphous phase. Almost liquid-like super-ionic diffusion is observed in AIMD simulations of the three structures at high temperatures; with predicted onset temperatures of 1800 K, 1200 K, and 600 K in the perfect structure, vacancy structure and the amorphous phase, respectively. In the ideal structure, the Li atoms show correlated jumps; while simple and correlated jumps are both seen in the vacancy structure, and a mix of jumps and continuous diffusion occur in the amorphous structure. Further, we find that the Li-diffusion is favored in all cases by a large librational amplitude of the neighbouring AlO4 tetrahedra, and that the amorphous structure opens additional diffusion pathways due to a broad distribution of AlO4 tetrahedra orientations.

An Insight into nd10 Metal Cyanide‐based Coordination Polymers Through ab‐initio Calculations: Electronic Properties and Optical Response

“…Coordination polymers based on transition metal cyanides, whose constituent metals have a fully populated d-shell (nd 10 ), constitute a family of materials with uncommon physical properties like the negative thermal expansion (NTE), which has been explained through the activation of low energy transversal phonon modes on heating. [1,2] They also have been used for some other applications such like catalysis, [3,4] sensors [5,6] and adsorption. [7] Six compounds are studied herein, the first ones consist of CuCN, AgCN and AuCN.…”

A general expression for the statistical error in a diffusion coefficient obtained from a solid‐state molecular‐dynamics simulation

“…This variant is commonly used to analyze data from ab‐initio MD, 22,31,51–54 with the aim of reducing the considerable statistical scatter that arises from small particle numbers (cell sizes) and run times. By virtue of providing smooth curves, this variant is very useful for the identification of the ballistic regime 31 and of anomalous diffusion on small time scales 55–58 .…”

Soft anharmonic coupled vibrations of Li and SiO4 enable Li-ion diffusion in amorphous Li2Si2O5

“…We have adopted a similar approach for amorphous structure generation as described in ref. 31 , 33 and 47 .…”

“…25 In a few earlier studies on many superionics, the importance of low- E phonons in crystalline solids in facilitating cation diffusion has been identified. 31,32 These low- E phonon dynamics in framework structure compounds enhance the cationic conductivity via modulating the dimension of cation pathways and/or via a paddle wheel mechanism. 33,34 Hence, studying low- E dynamics is important for potential superionics or solid-state electrolytes.…”