Exploring the diffusion mechanism of Li ions in different modulated arrangements of La(1-X)/3LixNbO3 with fitted force fields obtained via a metaheuristic algorithm

Abstract

As a potential solid-state electrolyte material, Li-containing A-site deficient perovskite oxides have attracted the attention of researchers because of their high Li-ion conductivity and the relationship between Li-ion conduction and structural characteristics, which has been intensively investigated. We have recently confirmed a quasi-periodic ordered arrangement of La and vacancies (Vac) at the perovskite A-sites of LixLa(1-x)/3NbO3 (LLNO) using a combination of density functional theory (DFT), Monte Carlo simulations, and electron diffraction. Interestingly, two types of modulated arrangements, namely closed and striped structures, coexist in the La-rich layer, which affect Li-ion migration. In this study, DFT-derived force-field molecular dynamics (FFMD) simulations were performed to investigate the effect of a modulated structure on the migration behavior of Li ions in LLNO compounds. The results indicate that the type of modulated arrangements of La/Vac has a significant influence on the migration of Li ions. Moreover, the estimated diffusion coefficients of the modulated structures are higher by a factor of 10 than those of La/Vac disordered models at 800 K. The migration energy in the ab plane appeared to be much lower than along the c-axis, controlling the modulated arrangement of LLNO is beneficial to eliminate La-ion blockage during long-distance migration. Accordingly, the present study reveals that the controlling cation/Vac arrangement at perovskite A-sites is crucial for achieving high Li-ion conductivity. At the same time, the research scheme of this work is also applicable to other solid electrolyte materials, which provides research guidance for high-throughput material retrieval.