NaMoO₂: a Layered Oxide with Molybdenum Clusters.

Area of Science:

• Solid-state chemistry
• Materials science
• Inorganic chemistry

Background:

• Layered oxides are crucial in energy storage applications.
• Understanding the structure-property relationships of novel materials is key to advancing battery technology.
• Sodium molybdenum oxides (NaₓMoO₂) are being explored for sodium-ion batteries.

Purpose of the Study:

• To synthesize and characterize a new layered oxide, NaMoO₂.
• To investigate the structural, electronic, and magnetic properties of NaMoO₂.
• To evaluate NaMoO₂ as a potential electrode material for sodium batteries.

Main Methods:

• Synthesis of NaMoO₂ via reaction of Na₂/₃MoO₂ with sodium metal.
• Structure determination using high-resolution powder X-ray diffraction.
• Magnetic susceptibility measurements at low and room temperatures.
• Density Functional Theory (DFT) calculations.
• Fabrication and testing of a sodium battery prototype using NaMoO₂ as the positive electrode.

Main Results:

• NaMoO₂ was successfully synthesized as a layered oxide with a distorted α-NaFeO₂ structure.
• Evidence of "diamond-like" molybdenum clusters due to Peierls distortion was observed, with short Mo-Mo distances (2.58 Å).
• NaMoO₂ exhibits very low magnetic susceptibility, indicating 4d electron localization in Mo-Mo bonds, confirmed as diamagnetic at 0 K by DFT.
• Reversible deintercalation and intercalation of sodium ions were demonstrated in a sodium battery prototype.

Conclusions:

• NaMoO₂ is a novel layered oxide with unique structural and electronic properties.
• The material's diamagnetic nature and electron localization suggest potential for stable electrochemical performance.
• NaMoO₂ shows promise as a positive electrode material for sodium-ion batteries, contributing to the understanding of the NaₓMoO₂ system.