Elusive Co₂O₃: A Combined Experimental and Theoretical Study

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solid-State Chemistry

Background:

• Trivalent cobalt oxides (Co3+) are known, but the sesquioxide Co2O3 is elusive.
• Previous attempts to synthesize Co2O3 have been unsuccessful.

Purpose of the Study:

• Investigate the structural stability of Co2O3.
• Examine the properties of solid solutions where Co3+ partially substitutes Ln3+ in Ln2O3.

Main Methods:

• Ab initio-based density functional theory (DFT)
• Accelerated Integrated Molecular Dynamics (AIMD)
• Crystal Orbital Hamiltonian Population (COHP) analysis

Main Results:

• AIMD simulations indicate that Co2O3 in a corundum structure is unstable.
• COHP analysis reveals inherent instability in Co2O3 structures.
• Solid solutions (Ln0.5Co0.5)2O3 (Ln = Y, Lu) with a cubic bixbyite structure are stable, with Co3+ in an intermediate-spin state.

Conclusions:

• Pure Co2O3 is structurally unstable.
• The bixbyite structure in (Ln0.5Co0.5)2O3 solid solutions provides stability for Co3+ ions.
• This work provides insights into the stabilization of trivalent cobalt in oxide materials.