Electric field‐assisted solid‐state reaction of BaCO₃‐TiO₂ system

Abstract

We report phase transition process during the solid-state reaction of BaCO 3 -TiO 2 system under the assistance of electric field. Experiments were conducted at a constant heating rate with preset field strength and current limit. Solid-state reaction was completed upon reactive flash sintering taking place at ~1002℃ under 200 V/cm. Hexagonal BaTiO 3 phase, which rarely occurs at such temperatures, was obtained after flash sintering at a current density of 23.5 mA/mm 2 . It is speculated that oxygen deficiency during flash sintering triggered cubic-to-hexagonal transition of BaTiO 3 . Furthermore, X-ray diffraction results show that solid-state reaction takes place prior to flash sintering. Electric field could accelerate the reaction but did not alter the sequence of phase evolution.

The influence of the processing parameters on the reactive flash sintering of ZrO2‐CeO2

“…The electrochemical reactions that happened when using DC mode were also observed in Na 3 Zr 2 (SiO 4 ) 2 (PO 4 ) 44 with the formation of a secondary phase, Na 2 ZrSi 2 O 7 , and accumulation of NaO x at the cathode. DC reducing effects were also observed in air in the literature when creating defect fluorite phases of Gd 2 Zr 2 O 7 , 32 and also by triggering cubic to hexagonal phase transitions in BaTiO 3 33 …”

“…DC reducing effects were also observed in 32 and also by triggering cubic to hexagonal phase transitions in BaTiO 3 . 33 Intensity of the reactions was dictated by the maximum current density achieved during RFS. Tests under the same condition (onset at 1200 • C und 250 V⋅cm −1 , AC mode, in air) at different current densities indicated that a certain current density intensity is necessary to promote full reac-tion.…”

“…AC electric fields can also be used to produce pyrochlore phases, such as (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Zr 2 O 7 , from a mixed oxide powder precursor in oxygen‐deficient atmosphere 37 . On the other hand, DC fields can induce defect formations such as oxygen deficiency in some oxide materials 33 . Finally, from the current understanding on RFS, it can also be concluded that high current densities usually enhance the phase reactions and sintering rates 34,38,39,41,43 but, if the current density increases above a certain threshold, it can cause damages to the material 40 …”

“…It was demonstrated recently that FS can induce solid‐state reactions to produce a single‐phase, dense, and nanostructured polycrystalline mixed oxide in 1 minute from a mix of its elemental oxides 27 . This method was named reaction flash sintering or reactive flash sintering (RFS) 27–29 and it has been used to produce BiFeO 3 , 27 MgAl 2 O 4 , 30 PbO‐ZrO 2 ‐TiO 2 , 31 Gd 2 Zr 2 O 7 , 32 BaTiO 3 , 33 Li 5.95 Al 0.35 La 3 Zr 2 O 12 , 34 (Bi 0.2 Na 0.2 K 0.2 Ba 0.2 Ca 0.2 )TiO 3 , 35 Mg 0.2 Ni 0.2 Co 0.2 Cu 0.2 Zn 0.2 O, 36 and (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Zr 2 O 7 37 from a mix of their oxide powder precursors. Alternatively, RFS also works with powder precursors prepared by chemical synthesis methods 29,38 .…”

Reactive Flash Sintering of Ceramics: A Review

“…[ 52 ] This effect would apply even in the absence of the flash event. As a matter of fact, during RFS of CCTO [ 46 ] (starting with an amorphous powder) and BTO [ 56 ] crystallization/reactions took place during Stage I, i.e., prior to the flash event, when Joule heating is small. Furthermore, in these instances, there is no contribution from the rapid rise in temperature (thermal runaway) to accelerate the synthesis rate.…”