Unexpected formation by pulsed laser deposition of nanostructured Fe/olivine thin films on MgO substrates

Olivine-type LiFePO4 thin films were grown on MgO (1 0 0) substrates by pulsed laser deposition (PLD). The formation of an original nanostructure is evidenced by transmission electron microscopy measurements. Indeed, on focused ion beam prepared cross sections of the thin film, we observe, the amazing formation of metallic iron/olivine nanostructures. The appearance of such a structure is explained owing to a topotactic relation between the two phases as well as a strong Mg diffusion from the substrate to the film surface. Magnesium migration is thus concomitant with the creation of metallic iron domains that grow from the core of the film to the surface leading to large protuberances. To the best of our knowledge, this is the first report on iron extrusion from the olivine-type LiFePO4.

Graphical AbstractHRTEM image of olivine/Fe nanostructure obtained by PLD. Figure optionsDownload as PowerPoint slideResearch highlights
► This manuscript describes the attempt to prepare textured LiFePO4 by PLD. This is presently a challenge to better understand the physical properties of the material, used as cathode in lithium ion batteries.
► We describe for the first time the iron extrusion from this material. Indeed, there were recent reports on the possible non-stoichiometry, i.e. lithium or oxygen. However, on the iron side, only some defect were observed for hydrothermally prepared material but the extrusion is new in this paper.
► We prepared interesting nanostructures which could be used for different fundamental studies: electric and magnetic measurements.