Direct observation of V-trimers in the crystal structure of LiVO₂

Although a trimerized ground state has been predicted for LiVO₂ for over half a century, the direct determination of its crystal structure in the trimerized phase by X-ray diffraction remains elusive. Depending on the cooling process, two distinct structural modifications have been prepared - LiVO₂ with streak-like, smeared-out superstructure reflection intensities and Li_0.91VO₂ with well-separated superstructure reflection intensities. The discovery of well-separated superstructure reflections in Li_0.91VO₂ enabled us to solve its crystal structure. This motivated us to attribute the streak-like superstructure reflection intensities in LiVO₂ to an overlap of reflections due to a unit cell doubling along the c-axis, which contrasts with the previous interpretation of randomly stacked V trimer layers. The availability of the crystal structure data forms a starting point for the quantitative modeling of the trimerization phenomenon in this complex Mott insulator.