Pyrochlore phase in the Bi2O3–Fe2O3–WO3–(H2O) system: Physicochemical and hydrodynamic aspects of its production using a microreactor with intensively swirled flows

Abstract

The present work deals with a study of physicochemical and hydrodynamic aspects of a new approach to the synthesis of a (Bi,Fe, □)2(Fe,W)2O6O′δ cubic pyrochlore-structured phase (hereinafter BFWO) in the Bi2O3–Fe2O3–WO3–(H2O) system. The considered approach is based on the use of microreactor technology at the stage of obtaining the amorphous precursor suspension, which is subsequently hydrothermally treated. The amorphous precursor suspension was obtained by co-precipitation method using two techniques of mixing reagent solutions, namely (i) by dropwise supply (traditional laboratory technique), and (ii) by intensive co-precipitation in a microreactor with a continuous supply of swirling flows of reagent solutions (microreactor technology with a suspension output of ∼ 7 L/min). It is shown that the microreactor strategy made it possible to avoid the spatial isolation of components during the amorphous precursor formation, which further ensured the formation of crystals of only the BFWO phase (without impurities). The values of the band gap (Eg) for direct allowed electronic transitions are 2.40 ± 0.03 and 2.35 ± 0.03 eV for the microreactor case and for the dropwise supply, respectively, which permits characterization of the obtained materials as wide bandgap semiconductors.