A study of phase evolution of Fe-doped bismuth tantalate pyrochlore

The phase formation process of Bi2FeTa2O9.5 (sp. gr. Fd-3m) synthesized by traditional ceramic technology was studied. Bismuth orthotantalate BiTaO4 (sp. gr. Pnna) was found to be the precursor of the pyrochlore phase. The high-temperature synthesis of the iron-containing pyrochlore and the formation of a characteristic dendrite-like microstructure took place at temperatures above 900°С. The pure pyrochlore was obtained at a temperature of 1050°С. At the early stages of calcination, at a temperature close to 650 °C, the main part of iron (III) oxide, as a precursor, interacts with bismuth tantalate, and at temperatures above 950 °C, no Fe2O3 traces in the sample were found. Complex oxides Bi25FeO40 (sp. gr. I23), Bi3TaO7 (sp. gr. Fm-3m) were found as intermediate phases during the synthesis of pyrochlore. Pyrochlore of the given composition Bi2FeTa2O9.5 had a porous microstructure with a grain size of 0.5–1.0 μm. The calcination temperature did not significantly affect the microstructure of the sample. The porosity of synthesized samples with a pyrochlore structure does not exceed 21%.