Modeling Short-Range Order in Disordered Rocksalt Cathodes by Pair Distribution Function Analysis

Nathan J. Szymanski; Zhengyan Lun; Jue Liu; Ethan C. Self; Christopher J. Bartel; Jagjit Nanda; Bin Ouyang; Gerbrand Ceder

doi:10.1021/acs.chemmater.2c03827

Modeling Short-Range Order in Disordered Rocksalt Cathodes by Pair Distribution Function Analysis

Nathan J. Szymanski, Zhengyan Lun, Jue Liu, Ethan C. Self, Christopher J. Bartel, Jagjit Nanda, Bin Ouyang, Gerbrand Ceder

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15 Scopus citations

Abstract

Pair distribution function (PDF) analysis is a powerful technique for the characterization of short-range order (SRO) in disordered materials. Accurate interpretation of experimental PDF data is critically reliant on the development of structural models that can account for local variations in site occupancies and bond lengths. To this end, we outline an approach to model SRO using first-principles calculations based on the cluster-expansion formalism. These methods are validated on neutron scattering data from two disordered rocksalt oxyfluorides, Li_1.3Mn_0.4Ti_0.3O_1.7F_0.3 and Li_1.3Mn_0.4Nb_0.2Ti_0.1O_1.7F_0.3. For each composition, we demonstrate that an average structure without any SRO fails to reproduce several key features in the experimental PDF. To pinpoint the origin of the suspected SRO in these materials, configurational and displacive effects were separately investigated using two disparate models. Special quasi-random structures were relaxed using density functional theory to account for local changes in bond lengths while maintaining a near-random ionic configuration. This leads to slightly improved accuracy but still misrepresents asymmetry in the first few peaks of the PDF. Monte Carlo simulations were performed to model configurational SRO on a fixed lattice, which by itself is shown to have a minimal influence on the PDF. Instead, we find that it is the bond length relaxations within environments created by SRO which controls the details of the PDF, thereby highlighting the subtle but important coupling between configurational and displacive SRO in disordered materials.

Original language	English
Pages (from-to)	4922-4934
Number of pages	13
Journal	Chemistry of Materials
Volume	35
Issue number	13
DOIs	https://doi.org/10.1021/acs.chemmater.2c03827
State	Published - Jul 11 2023

Funding

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, under the Applied Battery Materials Program of the U.S. Department of Energy (DOE) under contract no. DE-AC02-05CH11231. Computations were performed using resources provided by the Extreme Science and Engineering Discovery Environment (XSEDE), supported by the National Science Foundation under grant number ACI1053575. We also acknowledge support from the National Science Foundation Graduate Research Fellowship under grant number 1752814. Neutron powder diffraction measurements used resources at the Spallation Neutron Source (NOMAD instrument), a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. J.L. would like to thank the partial financial support from ORNL DRD #10740─Automatic Structure Refinement Platform (ASRP) for neutron diffraction.

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10.1021/acs.chemmater.2c03827

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title = "Modeling Short-Range Order in Disordered Rocksalt Cathodes by Pair Distribution Function Analysis",

abstract = "Pair distribution function (PDF) analysis is a powerful technique for the characterization of short-range order (SRO) in disordered materials. Accurate interpretation of experimental PDF data is critically reliant on the development of structural models that can account for local variations in site occupancies and bond lengths. To this end, we outline an approach to model SRO using first-principles calculations based on the cluster-expansion formalism. These methods are validated on neutron scattering data from two disordered rocksalt oxyfluorides, Li1.3Mn0.4Ti0.3O1.7F0.3 and Li1.3Mn0.4Nb0.2Ti0.1O1.7F0.3. For each composition, we demonstrate that an average structure without any SRO fails to reproduce several key features in the experimental PDF. To pinpoint the origin of the suspected SRO in these materials, configurational and displacive effects were separately investigated using two disparate models. Special quasi-random structures were relaxed using density functional theory to account for local changes in bond lengths while maintaining a near-random ionic configuration. This leads to slightly improved accuracy but still misrepresents asymmetry in the first few peaks of the PDF. Monte Carlo simulations were performed to model configurational SRO on a fixed lattice, which by itself is shown to have a minimal influence on the PDF. Instead, we find that it is the bond length relaxations within environments created by SRO which controls the details of the PDF, thereby highlighting the subtle but important coupling between configurational and displacive SRO in disordered materials.",

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AU - Ouyang, Bin

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Modeling Short-Range Order in Disordered Rocksalt Cathodes by Pair Distribution Function Analysis

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