Original Layered OP4-(Li,Na)CoO₂ Phase: Insights on Its Structure, Electronic Structure, and Dynamics from Solid...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Inorganic Chemistry

Background:

• The OP4-Li/NaCoO₂ phase presents a unique lamellar oxide structure with alternating Li and Na interslab spaces.
• Understanding its local structure, electronic properties, and ion dynamics is crucial for potential applications.

Purpose of the Study:

• To investigate the local structure, electronic structure, and dynamics of the OP4-(Li/Na)CoO₂ phase.
• To complement X-ray diffraction (XRD) and electronic/magnetic property measurements with nuclear magnetic resonance (NMR) spectroscopy.

Main Methods:

• ⁷Li and ²³Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy.
• X-ray diffraction (XRD) with Rietveld refinement.
• Electronic and magnetic properties measurements.

Main Results:

• ⁷Li MAS NMR indicated unusual NMR shifts from both Fermi contact and Knight shifts, suggesting localized and delocalized electrons.
• Multiple Li environments and varied Co ion electronic structures were observed, potentially influenced by Na⁺ ion arrangement.
• ²³Na MAS NMR revealed Na⁺ ions in Li layers, contrary to prior structural models, and significant Na⁺ ionic mobility at room temperature.

Conclusions:

• The study provides new insights into the complex local structure and electronic properties of OP4-Li/NaCoO₂.
• NMR spectroscopy revealed unexpected cationic arrangements and dynamics, refining the understanding of this lamellar oxide.
• Significant differences in Li⁺ and Na⁺ ionic mobility were quantified, with Na⁺ exhibiting much higher mobility.