Flash sintering of highly insulating nanostructured phase‐pure BiFeO₃

Abstract

We show that BiFeO 3 , that is electrically homogeneous, is a good insulator, and has a low dielectric constant (the properties desired in its applications), can be produced by flash sintering, which is nominally difficult to achieve by conventional and spark plasma sintering processes. The flash-sintered specimens had a uniform microstructure with a nanometric grain size of~20 nm. K E Y W O R D SBiFeO 3 , electrically homogeneous, flash sintering, high purity, insulating, nanostructured

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

“…The results, showing the power dissipation and shrinkage as a function of furnace temperature for the three compositions are shown in Figure . The curves are similar to those obtained for unsubstituted BF specimens which were also flashed with 50 V cm −1 and 40 mA mm −2 …”

“…At the onset of flash, there is a sharp increase in the conductivity, which is called Stage II. The furnace temperatures for the onsets of flash are in the range 630‐660°C for the BF(La, Sm, and Y) samples, which are slightly higher than the furnace temperature for the onset of flash for BF flash sintered at a DC electric field of 50 V cm −1 (~605°C) …”

“…The electrical processing parameters for flash sintering consist of (a) a combination of electric field and furnace temperature for the onset of the flash, and (b) the current density just after the onset. There is often a wide window for (a) so that flash can be instituted under a range of fields and temperatures (a higher field lowers the temperature of the furnace for flash), which was the case in experiments with BF . The same experimental conditions were found to apply for flash sintering of BF(La, Sm, and Y) powders.…”

“…Figure gives the micrographs and the grain size distribution histograms of the flash sintered samples. They have a similar microstructure, typical of BF‐related materials sintered by flash . They are composed of nano‐scale grains with average sizes of 28 ± 8, 25 ± 5, and 22 ± 6 nm for BF(La), BF(Sm), and BF(Y), respectively.…”

“…The above powders were uniaxially pressed at 500 MPa into dog bone‐shaped green bodies, with a gage length of 21 mm and a rectangular cross section of 4.74 mm 2 . The dog bones were flash sintered, using the same procedure as used for BF . The samples were placed into a tubular furnace by means of two platinum wires attached to the handles of the dog bone.…”