Phase-pure BiFeO₃ produced by reaction flash-sintering of Bi₂O₃ and Fe₂O₃

Abstract

Mixed powders of Bi2O3 and Fe2O3 are shown to yield single-phase, dense nanostructured polycrystals of BiFeO3 in reaction flash sintering experiments, carried out by applying a field of 50 V cm -1 and with the current limit set to 35 mA mm -2 . The furnace was heated at a constant rate with the reaction sintering taking place abruptly upon reaching 625 o C.Remarkably, an intermediate bismuth-rich phase of the oxide that forms just before reaching the flash temperature, transforms, and at the same time sinters, into single-phase BiFeO3 within a few seconds after the onset of the flash. The BiFeO3 so produced is electrically insulating, a property that is critical to its applications. This one-step synthesis of single-phase polycrystals of complex oxides from their basic constituents, by reaction flash sintering, is a significant development in the processing of complex oxides, which are normally difficult to sinter by conventional methods.

Processing and properties of Bi0.98R0.02FeO3 (R = La, Sm, Y) ceramics flash sintered at ~650°C in <5 s

“…In summary, the Néel temperatures and also the Curie temperatures for flash sintered samples are in very good agreement with those of high quality samples reported in literature …”

Reactive flash sintering of powders of four constituents into a single phase of a complex oxide in a few seconds below 700°C

“…Low melting bismuth, and myriad phases that form below the sintering temperature makes it difficult to obtain phase pure ceramic with good electrical properties. 3 Similarly mixtures of alumina and magnesia have been shown to form single phase spinel 4 ; in situ experiments have shown that in this case, phase transformation is completed a little sooner than sintering. 2 Furthermore it has been shown that mixtures of elemental powders of bismuth oxide and iron oxide can be transformed into dense single phase polycrystals, also in a few seconds, which we call reactive flash sintering (RFS).…”

“…2 Furthermore it has been shown that mixtures of elemental powders of bismuth oxide and iron oxide can be transformed into dense single phase polycrystals, also in a few seconds, which we call reactive flash sintering (RFS). 3 Similarly mixtures of alumina and magnesia have been shown to form single phase spinel 4 ; in situ experiments have shown that in this case, phase transformation is completed a little sooner than sintering. 5 In the present work, reactive flash sintering is expanded to LLZO(Al) which is constituted from oxides of Li, La, Zr, and Al.…”

On the synchronicity of flash sintering and phase transformation

“…Recent experiments, with bismuth oxide and ferric oxide to form bismuth ferrite, and with reactions between alumina and magnesia to form spinel, have shown that phase transformations and sintering can occur together during a flash experiment. Conventional sintering usually requires stoichiometric powders, adding significant cost to manufacturing.…”

“…The discovery of flash sintering is evolving into a process for the synthesis of multiconstituent ceramics that are difficult to make by conventional methods. Powders of elemental components can be mixed and flashed in mere seconds to produce single‐phase oxides of complex compositions . The phase transformation and sintering occur concomitantly.…”