Atomic structures of twin boundaries in CoO

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Crystals with face-centered-cubic (FCC) structures typically exhibit (111) twinning planes.
• This is observed in FCC metals and oxides like NiO and Fe3O4.
• Cobalt oxide (CoO) is a rock-salt-type material.

Purpose of the Study:

• To investigate the twinning plane of rock-salt-type CoO.
• To analyze the atomic and electronic structures of the CoO(112) twin boundary.
• To compare the stability of the (112) twin boundary with the conventional (111) twin boundary.

Main Methods:

• Aberration-corrected scanning transmission electron microscopy (STEM).
• Electron-energy-loss spectroscopy (EELS).
• Density functional theory (DFT) calculations.

Main Results:

• The twinning plane of rock-salt-type CoO was identified as (112), deviating from the typical (111) plane.
• Atoms at the (112) twin boundary maintain nominal oxidation states.
• The (112) twin boundary is insulating and exhibits antiferromagnetic coupling.
• Electronic structure and crystal orbital Hamilton population (COHP) analyses indicate the (112) twin boundary is more stable than the (111) twin boundary.

Conclusions:

• The (112) plane is the predominant twinning plane in rock-salt-type CoO.
• The identified (112) twin boundary possesses unique electronic and magnetic properties.
• The greater stability of the (112) twin boundary influences crystal growth and properties.