Combined Multiple Scattering Simulation and Hartree-Fock LCAO Studies of Atomic Displacements in Li_xV₂O₅

Abstract
Lithium intercalation into the lamellar vanadium oxide Li_xV₂O₅ is only reversible below x ≈ 0.9. Insertion of larger amounts induces an irreversible phase transition that destroys the 2D character of the host. This structural change is due to atomic displacements that lead from distorted square pyramidal V₂O₅clusters to V₂O₆ octahedra [1]. In-situ XAS studies at the vanadium K edge of lithium intercalation into V₂O₅ confirmed this local increase of the symmetry and established that, not only oxygen but also vanadium, move from their initial sites, as the intercalation proceeds [2]. Starting from this structural model, we performed multiple scattering simulation (CONTINUUM code) to understand the changes observed in the experimental XANES spectra. These calculations explain the new features appearing in the edge as the lithium rate increases. Hartree-Fock LCAO calculations (CRYSTAL 92 code) have also betn used to discuss the stability of the proposed structural models, taking into account both atomic displacements and lithium intercalation.