Atomic modeling of the δ ↔ ε LiV2O5 phase transition and simulation of the XRD powder pattern evolution

delta and epsilon LiV2O5 crystallize in the orthorhombic system, with Cmcm and Pmmn space groups, respectively. Transformation of delta into epsilon is initiated at about approximately 110 degrees C. In both structures, lithium atoms are intercalated between [V2O5](n) layers built up by VO5 square pyramids sharing edges and corners, these layers being alternatively half shifted along the 3.6 Angstrom parameter in the delta phase. Both crystal structures have been accurately depicted using Pmn2(1) space group with the short parameter along c. The phase transition, corresponding to a slip of c/2 of the alternate [V2O5](n) layer of delta together with some lithiums, has been modeled step by step in order to be aligned along c, to finally match the epsilon structural organization. The shift vector s applied to z coordinates varies from 0 less than or equal to s less than or equal to 0.5. The resulting evolution of the sequence of the computed X-ray powder pattern compares well with the experimental one done at ESRF (lambda. = 0.64667). The joint structural modeling and X-ray patterns account for the delta double left right arrow epsilon LiV2O5 phase transition. (C) 1999 Academic Press.