Lattice constant anomaly in the Li1+xV1-xO2 system near x=0

Polycrystalline powders of Li1+xV1-xO2 were prepared in the composition range -0.10 <= x <= 0.30 via the solid state technique. X-ray diffraction indicated single phase, layered R (3) over barm structure material with the exception of some impurity phases for x >= 0.15. Analysis of powder X-ray diffraction patterns revealed an anomaly in the lattice parameters centered near x = 0. The c-axis of the hexagonal representation was at a maximum for this composition and the a-axis at a minimum. Careful X-ray diffraction scans observed the well-known superlattice peak, which is due to trimer formation in LiVO2 - a periodic lattice distortion within the plane of vanadium cations. Integrating the areas of the Li1+xV1-xO2 superlattice peaks revealed a strong correlation between composition, fraction of vanadium in the V3+ oxidation state, lattice parameter, and degree of trimer formation. These results may suggest the view of trimer formation as a consequence of vanadium t(2g) orbital ordering.