Nanoscale BiFeO precipitates in BiFeO thin films: a metastable Aurivillius phase.

We report the observation of nano-scale precipitates corresponding to a new structure not displayed by the phase diagram of bismuth iron oxide. BiFeO (BFO) thin films grown on terbium scandate and strontium titanate substrates by pulsed laser deposition were investigated using high-resolution transmission and scanning transmission electron microscopy. Precipitate-like structures with a so far unknown metastable phase of bismuth, iron, and oxygen were observed in these films. They consist of well-ordered BiO layers, as they are known from bismuth oxide layered compounds. They have a pseudo-orthorhombic structure with a single perovskite-like unit (FeO) sandwiched between BiO layers, similar to the Aurivillius phase BiWO, with a chemical composition of the precipitates of BiFeO. The structure of the new phase with its lattice constants was elucidated and the band gap of the precipitates was determined by electron energy loss spectroscopy. The results point to promising future applications for this new phase in the field of electronics, if it might be grown phase pure as an epitaxial thin film. [ABSTRACT FROM AUTHOR]