Influence of annealing temperature on microstructure and phase transformations of oxide system Bi2O3/TiO2 formed in aqueous solutions

Bismuth titanate is widely used in various fields of science and technology due to its unique physical and chemical properties. Nanostructured metal oxide compounds of the Bi–Ti–O system, consisting of columnar TiO₂ nanostructures obtained by electrochemical anodization of a two-layer Ti/Al composition, and platelet Bi₂O₃ nanostructures formed by sequential ion-layer deposition were synthesized. Morphological changes and phase transformations in the microstructure of the Bi₂O₃/TiO₂ oxide system, which occur during its thermal annealing at temperatures of 150, 300, 500, and 700 °C, have been studied. Annealing of the oxide system in the range of 150–300 °C degrees leads to inconsequential morphological and structural changes: the mixture of oxides is densified, in addition to anatase, a rutile phase appears in TiO₂. The crystal system of the Bi₂O₃ phase is hexagonal. After annealing at 500 °C, not only morphological changes occurred in the studied composite, but also significant transformations in the microstructure. In the film volume, oxide phases Ti₂O₃ and Bi₂O₃ began to transform into three-component compound Bi₄Ti₃O₁₂, and this process is completed at 700 degrees with the formation of single-phase Bi₄Ti₃O₁₂ nanocomposite with an orthorhombic lattice with the crystal space group Fmmm.