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This paper reports a thorough microstructural investigation of bismuth ferrite (BFO) thin films subjected to various processing conditions and discusses their influence on the stability of the BiFeO 3 perovskite phase. The formation of secondary phases in BFO thin films is studied as a function of annealing temperature and time, film thickness, Bi excess, and Ti substitution. While films annealed at 600°C consist of the desired BiFeO 3 phase, higher temperatures induce the decomposition leading to a significant amount of secondary phases, particularly the iron-rich Bi 2 Fe 4 O 9 phase. A longer annealing time at 700°C further enhances the decomposition of BiFeO 3 . Qualitative microstructural analysis of the films is performed by electron backscattered diffraction which provides phase analysis of individual grains. The morphology of the single-crystalline Bi 2 Fe 4 O 9 grains that are embedded in the BiFeO 3 matrix drastically changes as a function of the film thickness. Nucleation of these Bi 2 Fe 4 O 9 grains probably occurs at the film/substrate interface, after which grain growth continues toward the surface of the film through the depletion of the BFO phase. Addition of Bi excess or the substitution of Fe with Ti in the precursor solutions significantly reduces the formation of an iron-rich secondary phase. Influence of the secondary phases as well as Ti substitution on magnetic properties of BFO films was investigated.

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Bismuth titanate based nanopowders with the different content of La or Ce were synthesized by the modified sol-gel method. After calcination at 600?C, in addition to Aurivillius layered structure, a small quantity of cubic pyrochlore phase was detected in the La modified powders, while this second phase was much more pronounced in the Ce substituted powders. In fact, as the powder with the highest amount of Ce (Bi3CeTi3O12) has the pure pyrochlore phase it seems that the presence of Ce stabilizes the formation of this phase. This different influence of cerium and lanthanum could be explained by the incorporation of their ions on the different sites in the titanate structure. Bismuth titanate based ceramics, sintered at 1050?C/2h, had densities above 93% of theoretical density and characteristic plate-like grain morphology. Small quantity of cubic pyrochlore phase was detected only in the Ce modified bismuth titanate ceramics. On the other hand, lanthanum addition caused formation of smaller grain size with pronounced plate-like morphology. .

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