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 .

We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-resolution neutron powder diffraction toward understanding the phenomenon of magnetization reversal. Contrary to earlier reports, our study reveals that both C-type and G-type antiferromagnetic ordering, corresponding to G-type and C-type orbital ordered phases, respectively, occur at the same temperature (T N = 115 K) with the G-type antiferromagnetic phase growing at the expense of the C-type one on cooling. These processes cease at T S ∼ 77 K; however, a minor (∼4%) untransformed C-type phase remains unchanged down to 1.7 K. The symmetry analysis indicates different symmetry origins of the Dzyaloshinskii–Moriya interaction in each phase, which can explain the magnetization reversal observed between T N and T S. We discuss that magnetic phase separation and associated weak ferromagnetism may be the common mechanism underlying the magnetization reversal phenomenon observed in other RVO3 systems (R = rare earth).

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