Abstract
The interplay between the coordination environment and magnetic properties in O3 layered sodium transition metal oxides (NaTMO2) is a fascinating and complex problem. Through detailed and comprehensive density functional investigations on O3 NaTMO2 compounds, we demonstrate that the TM ions in O3 NaMnO2, NaFeO2 and NaCoO2 adopt a high spin state. Structurally, NaMnO2 and NaPdO2 undergo Jahn–Teller distortions while NaNbO2 undergoes puckering distortion. Furthermore, in addition to Jahn–Teller distortion, NaPdO2 exhibits charge disproportionation as it contains Pd2+, Pd3+ and Pd4+ species. These distortions stabilize the inter-plane ferromagnetism. Additionally, the inter-plane ferromagnetic coupling is stabilized by kinetic p–d exchange mechanism in undistorted NaCoO2, NaNiO2 and NaTcO2. The intra-plane coupling in this family of compounds on the other hand was found to be generally weak. Only NaMnO2, NaNiO2 and NaTcO2 are predicted to show bulk ferromagnetism with estimated Curie temperatures below ∼50 K.
Highlights
Layered hexagonal compounds with formula NaTMO2 in which TM is a transition metal o en exhibit interesting magnetic,[1,2,3] thermoelectric,[4] and electrochemical properties.[5]
We found that the total energy of the NaMnO2 compound rose by 1.306 eV/f.u. (f.u. is formula unit) when the Mn ion was set to low spin con guration (t2g4e0g)
We demonstrated that the rhombohedral distortion inherent to the 3Rm symmetry stabilizes G-type antiferromagnetism in NaTiO2, NaVO2, NaCrO2, NaFeO2, NaMoO2 and NaRuO2 compounds
Summary
Layered hexagonal compounds with formula NaTMO2 in which TM is a transition metal o en exhibit interesting magnetic,[1,2,3] thermoelectric,[4] and electrochemical properties.[5] One obstacle in studying these compounds is the rich variety of their polymorphs each with distinct symmetry and local coordination for the transition metal ions which complicates nding general property trends for this family of materials. One such area of research that lacks a concise overview is the magnetic properties of the NaTMO2 compounds. The notion “O3” indicates that oxygen ions are stacked in ABCABC order and Na ions occupy the octahedral
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