Features of phase formation of pyrochlore-type Bi2Cr1/6Mn1/6Fe1/6Co1/6Ni1/6Cu1/6Ta2O9+Δ

The study of the process of phase formation of multicomponent pyrochlore (Bi2−хCr1 / 6Mn1 / 6Fe1 / 6Co1 / 6Ni1 / 6Cu1 / 6Ta2O9+Δ) in the course of solid-phase synthesis showed that the precursor of the pyrochlore phase is bismuth orthotantalate. Of all the precursors, cobalt and nickel oxides are the last to enter the chemical reaction (at 850 – 900°С). Intermediate phases in the course of synthesis are complex oxides Bi16CrO27, Bi25FeO40, BiTaO4, Bi3TaO7, СoTa2O6. During the evolution of the pyrochlore phase, a nonmonotonic change in the unit cell parameter is observed. Phase-clean pyrochlore is synthesized at a temperature of 1000 –1050°С. Ceramics is characterized by a porous, loose microstructure with an average grain size of 0.5 –1 μm; the porosity of a sample calcined at 1050°С is 19 percent.