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Multiple twinning as a structure directing mechanism in layered rock-salt-type oxides: NaMnO2 polymorphism, redox potentials, and magnetism

Multiple twinning as a structure directing mechanism in layered rock-salt-type oxides: NaMnO2 polymorphism, redox potentials, and magnetism
Multiple twinning as a structure directing mechanism in layered rock-salt-type oxides: NaMnO2 polymorphism, redox potentials, and magnetism
New polymorphs of NaMnO2 have been observed using transmission electron microscopy and synchrotron X-ray powder diffraction. Coherent twin planes confined to the (NaMnO2) layers, parallel to the (101?) crystallographic planes of the monoclinic layered rock-salt-type ?-NaMnO2 (O3) structure, form quasi-periodic modulated sequences, with the known ?- and ?-NaMnO2 polymorphs as the two limiting cases. The energy difference between the polymorphic forms, estimated using a DFT-based structure relaxation, is on the scale of the typical thermal energies that results in a high degree of stacking disorder in these compounds. The results unveil the remarkable effect of the twin planes on both the magnetic and electrochemical properties. The polymorphism drives the magnetic ground state from a quasi-1D spin system for the geometrically frustrated ?-polymorph through a two-leg spin ladder for the intermediate stacking sequence toward a quasi-2D magnet for the ?-polymorph. A substantial increase of the equilibrium potential for Na deintercalation upon increasing the concentration of the twin planes is calculated, providing a possibility to tune the electrochemical potential of the layered rock-salt ABO2 cathodes by engineering the materials with a controlled concentration of twins.
0897-4756
3306-3315
Abakumov, Artem M.
af083db0-c7d5-4c08-885a-9ead9df1ba44
Tsirlin, Alexander A.
27bb96ec-f059-49e3-917d-009bf6b3aff9
Bakaimi, Ioanna
3c4e7000-517c-41fa-84db-c45641125e4d
Van Tendeloo, Gustaaf
4091da5b-98c3-4481-b706-a871c7b6d52e
Lappas, Alexandros
3e727545-5524-4bb7-a240-1c1aef2ce62d
Abakumov, Artem M.
af083db0-c7d5-4c08-885a-9ead9df1ba44
Tsirlin, Alexander A.
27bb96ec-f059-49e3-917d-009bf6b3aff9
Bakaimi, Ioanna
3c4e7000-517c-41fa-84db-c45641125e4d
Van Tendeloo, Gustaaf
4091da5b-98c3-4481-b706-a871c7b6d52e
Lappas, Alexandros
3e727545-5524-4bb7-a240-1c1aef2ce62d

Abakumov, Artem M., Tsirlin, Alexander A., Bakaimi, Ioanna, Van Tendeloo, Gustaaf and Lappas, Alexandros (2014) Multiple twinning as a structure directing mechanism in layered rock-salt-type oxides: NaMnO2 polymorphism, redox potentials, and magnetism. Chemistry of Materials, 26 (10), 3306-3315. (doi:10.1021/cm5011696).

Record type: Article

Abstract

New polymorphs of NaMnO2 have been observed using transmission electron microscopy and synchrotron X-ray powder diffraction. Coherent twin planes confined to the (NaMnO2) layers, parallel to the (101?) crystallographic planes of the monoclinic layered rock-salt-type ?-NaMnO2 (O3) structure, form quasi-periodic modulated sequences, with the known ?- and ?-NaMnO2 polymorphs as the two limiting cases. The energy difference between the polymorphic forms, estimated using a DFT-based structure relaxation, is on the scale of the typical thermal energies that results in a high degree of stacking disorder in these compounds. The results unveil the remarkable effect of the twin planes on both the magnetic and electrochemical properties. The polymorphism drives the magnetic ground state from a quasi-1D spin system for the geometrically frustrated ?-polymorph through a two-leg spin ladder for the intermediate stacking sequence toward a quasi-2D magnet for the ?-polymorph. A substantial increase of the equilibrium potential for Na deintercalation upon increasing the concentration of the twin planes is calculated, providing a possibility to tune the electrochemical potential of the layered rock-salt ABO2 cathodes by engineering the materials with a controlled concentration of twins.

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e-pub ahead of print date: 1 May 2014
Published date: 27 May 2014
Organisations: Chemistry

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Local EPrints ID: 403341
URI: http://eprints.soton.ac.uk/id/eprint/403341
ISSN: 0897-4756
PURE UUID: 22b962ec-d96e-473a-b74f-6816b84838b2
ORCID for Ioanna Bakaimi: ORCID iD orcid.org/0000-0002-8083-4413

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Date deposited: 30 Nov 2016 11:22
Last modified: 05 Nov 2019 01:28

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Author: Artem M. Abakumov
Author: Alexander A. Tsirlin
Author: Ioanna Bakaimi ORCID iD
Author: Gustaaf Van Tendeloo
Author: Alexandros Lappas

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