Multiple Twinning As a Structure Directing Mechanism in Layered Rock-Salt-Type Oxides: NaMnO2 Polymorphism, Redox Potentials, and Magnetism

• DOI: 10.1021/cm5011696
• Publication Date: 2014-05-01T15:43:17Z
• Authors: Artem M. Abakumov; Alexander A. Tsirlin; Ioanna Bakaimi; Gustaaf Van Tendeloo; Alexandros Lappas
• Keywords: Monoclinic crystal system; Magnetism; Monatomic ion

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 (101̅) crystallographic monoclinic layered rock-salt-type α-NaMnO2 (O3) structure, form quasi-periodic modulated sequences, with known α- β-NaMnO2 as two limiting cases. The energy difference between polymorphic forms, estimated a DFT-based structure relaxation, is on scale typical thermal energies that results in high degree stacking disorder these compounds. unveil remarkable effect both magnetic electrochemical properties. polymorphism drives ground state from quasi-1D spin system for geometrically frustrated α-polymorph through two-leg ladder intermediate sequence toward quasi-2D magnet β-polymorph. A substantial increase equilibrium potential Na deintercalation upon increasing concentration calculated, providing possibility tune rock-salt ABO2 cathodes by engineering materials controlled twins.