Formation of Bim + 1Fem – 3Ti3O3m + 3 (m = 4–9) Nanocrystals upon Thermal Decomposition of Coprecipitated Hydroxides

Nanocrystals of Bim + 1Fem – 3Ti3O3m + 3 (m = 4–9) Aurivillius phases were synthesized by thermal decomposition of a coprecipitated mixture of bismuth, iron, and titanium hydroxides. The average crystallite size in nanopowders depends on m and is 50–100 nm. The samples were characterized by simultaneous thermal analysis, elemental analysis, X-ray diffraction, and Mossbauer spectroscopy. It was shown that the onset of Bim + 1Fem – 3Ti3O3m + 3 crystallization is near the melting point of the bismuth oxide-based non-autonomous (surface) phase (450°C). The Bim + 1Fem – 3Ti3O3m + 3 compounds where m ≤ 5 crystallize in one stage. The compounds where m > 5 are formed in two stages. First, Aurivillius phases with m ≈ 5 and an amorphous phase are formed. Then, the components of the amorphous phase are incorporated into the perovskite-like blocks of the Aurivillius (m ≈ 5) phases, most likely through their outer perovskite-like layers. Then, the components are redistributed between the outer and inner layers of the perovskite-like blocks. The elucidated dependence of the formation mechanism of Bim + 1Fem – 3Ti3O3m + 3 nanocrystals on their composition can be used in the technology of directed synthesis of nanocrystalline multiferroics.