Exfoliated nanoplatelets of an Aurivillius phase, Bi 3.25La 0.75Ti 3O 12: Characterisation by X-ray diffraction and by high-resolution electron microscopy

Abstract

Nanoparticles of the Aurivillius phase La-substituted BTO (Bi 4− x La x Ti 3O 12, with x=0.75) were obtained through a chemical lithiation process. They have been characterised by X-ray diffraction and transmission electron microscopy (diffraction and imaging at high resolution). The defect-free particles are platelet-shaped with the c large axis perpendicular to the plane. From high-resolution images, it is clear that the delamination process occurs at the level of the (Bi 2O 2) 2+ intermediate layer and is destructive for this layer. The smallest thickness measured corresponds to one cell parameter (3.3 nm) but a large range of thicknesses have been observed: this suggests that the lithium insertion does not take place in all (Bi 2O 2) 2+ layers, despite a large excess of lithium and a long reaction time. This is confirmed by ICP analysis, which leads to a formula Li 0.99Bi 3.25La 0.77Ti 3.00O 12 for the lithiated compound. This behaviour towards lithium intercalation differs from those observed with BTO in literature, where lithium insertion is reported as occurring in every (Bi 2O 2) 2+ layer. Possible explanations for this difference are advanced based on microstructural and structural considerations.