New pyrochlores (sp. gr. Fd-3m) of Bi₂Mg(Zn)_1-хM_хTa₂O_9.5-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.