Effect of magnesium and zinc on phase formation of pyrochlore-type Bi2Mg(Zn)1-хMxTa2O9.5-Δ (M-Cr, Fe) ceramics

摘要

? 2022 Elsevier Ltd and Techna Group S.r.l.New pyrochlores (sp. gr. Fd-3m) of Bi2Mg(Zn)1-хMхTa2O9.5-Δ (M ? Cr, Fe) composition were obtained for the first time by the method of solid-phase synthesis. The process of phase formation of pyrochlores in the temperature range 650–1050°С was studied. It has been established that the precursor of the pyrochlore phase in all cases is orthorhombic bismuth orthotantalate BiTaO4. The pyrochlore phase synthesis reaction proceeds predominantly at temperatures above 850–900°С. The influence of magnesium and zinc on the course of pyrochlore synthesis was revealed. For chromium pyrochlores, the formation of intermediate phases such as Bi6Cr2O15, Bi16CrO27 was established; for iron-containing pyrochlores, Bi25FeO40 was identified as an intermediate phase. For all systems, the change in the parameter of the pyrochlore cell constant depending on the synthesis temperature was analyzed. The samples are characterized by a porous dendritic microstructure. The calcination temperature did not significantly affect the microstructure of the samples. The porosity of the samples was estimated. The optimal calcination temperature for obtaining phase-clean pyrochlores can be considered 1050°С.