Chemical Differences between K and Na in Alkali Cobaltates

Abstract

K${}_x$CoO${}_2$ shares many similarities with Na${}_x$CoO${}_2$, as well as some important differences (no hydration-induced superconductivity has been reported). At $T_{c2}$=20 K, K${}_{0.5}$CoO${}_2$ becomes an insulator with a tiny optical gap as happens in Na${}_{0.5}$CoO${}_2$ at 52 K. This similarity, with a known common structure, enables direct comparisons to be made. Using the K-zigzag structure recently reported and the local density approximation, we compare and contrast these cobaltates at x=0.5. Although the electronic structures are quite similar as expected, substantial differences are observed near the Fermi level. These differences are found to be attributable mostly to the chemical, rather than structural difference: although Na is normally considered to be fully ion, K has somewhat more highly ionic character than does Na in these cobaltates.

5 papers

References in corpus (16)

• Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)
• Low temperature phase transitions and crystal structure of Na0.5CoO2
• Charge Disproportionation and Spin Ordering Tendencies in Na(x)CoO2
• Magnetic Correlation of NaxCoO2 and Successive Phase Transitions of Na0.5CoO2 -NMR and Neutron Diffraction Studies-
• Neutron scattering study of novel magnetic order in Na0.5CoO2
• The Role of hybridization in NaxCoO2 and the Effect of Hydration
• Quasiparticle coherence and the nature of the metal-insulator phase transition in Na${}_x$CoO${}_2$
• Infrared spectroscopy of the charge ordering transition in Na${}_{0.5}$CoO${}_2$
• Disproportionation Transition at Critical Interaction Strength: Na${}_{1/2}$CoO${}_2$
• The infrared conductivity of Na${}_x$CoO${}_2$: evidence of gapped states
• Destruction of the small Fermi surfaces in Na${}_x$CoO${}_2$ by Na disorder
• Static magnetic order in metallic K${}_{0.49}$CoO${}_2$
• Charge and Spin Ordering in Insulating Na${}_{0.5}$CoO${}_2$: Effects of Correlation and Symmetry
• Magnetic and Metal-Insulator Transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 -NMR and Neutron Diffraction Studies-
• Infrared Conductivity and Charge Ordering in NaCoO2
• Electronic Structure of Sodium Cobalt Oxide: Comparing Mono- and Bilayer-hydrate

Cited by in corpus (5)

• Colossal Thermoelectric Power Factor in K${}_{7/8}$RhO${}_2$
• Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system LixCoO2
• Optical Study of the Electronic Structure and Correlation Effects in K0.49RhO2
• Enhanced Seebeck coefficient by a filling-induced Lifshitz transition in KxRhO2
• Ionic Hubbard model on a triangular lattice for Na_0.5CoO_2, Rb_0.5CoO_2 and K_0.5CoO_2: Mean-field slave boson theory