Elusive Co(2)O(3): A Combined Experimental and Theoretical Study

[Image: see text] Despite several oxides with trivalent cobalt ions are known, the sesquioxide M(2)O(3) with Co(3+) ions remains elusive. Our attempts to prepare Co(2)O(3) have failed. However, 50% of Co(3+) ions could be substituted for Ln(3+) ions in Ln(2)O(3) (Ln = Y and Lu) with a cubic bixbyite structure where the Co(3+) ions are in the intermediate-spin state. We have therefore examined the structural stability of Co(2)O(3) and the special features of solid solutions (Ln(0.5)Co(0.5))(2)O(3) (Ln = Y and Lu). The experimental results are interpreted in the context of ab initio-based density functional theory, molecular dynamics (AIMD), and crystal orbital Hamiltonian population (COHP) analysis. Our AIMD study signifies that Co(2)O(3) in a corundum structure is not stable. COHP analysis shows that there is instability in Co(2)O(3) structures, whereas Co and O have a predominantly bonding character in the bixbyite structure of the solid solution (Y(0.5)Co(0.5))(2)O(3).