A facile route to the synthesis of BiFeO3 at low temperature

Article abstract of DOI:10.1111/j.1551-2916.2011.04536.x

A facile sol-gel methodology based on the glycerol-gel reaction was used to prepare single-phase BiFeO₃ crystallites. The particle size and morphologies of BiFeO₃ crystallites were characterized by field-emission scanning electron mi

Full text of DOI:10.1111/j.1551-2916.2011.04536.x

J. Am. Ceram. Soc., 94 [9] 3060–3063 (2011)
DOI: 10.1111/j.1551-2916.2011.04536.x
r 2011 The American Ceramic Society
ournal
J
A Facile Route to the Synthesis of BiFeO at Low Temperature
3
z
w,y
z
y
Ting Liu, Yebin Xu, Shangshen Feng, and Jingyuan Zhao
z
Wuhan National Laboratory for Optoelectronics, School of Optoelectronic Science and Engineering, Huazhong
University of Science and Technology, Wuhan, Hubei 430074, China
yInstitute of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan,
Hubei 430074, China
zCollege of Physics and Electronic Engineering, Taizhou University, Linhai, Zhejiang 317000, China
A facile sol–gel methodology based on the glycerol-gel reaction
was used to prepare single-phase BiFeO crystallites. The par-
more OH groups and less COOH groups, but no experimental
proof was provided. As we known, glycerol has three hydroxyl
groups and no COOH groups, and it can form complexes with
many metal ions. Therefore, maybe glycerol is a new complexing
3
ticle size and morphologies of BiFeO crystallites were charac-
3
terized by field-emission scanning electron microscope and
transmission electron microscope. X-ray diffraction results in-
dicated that single-phase and well-crystallized BiFeO has been
agent to prepare pure BiFeO . In this paper, glycerol route was
3
used to prepare BiFeO and well-crystallized BiFeO has been
3
3
3
synthesized at the temperature as low as 4001C. In present
synthesized at the temperature of 4001–6001C.
work, single-phase BiFeO can be formed at lower temperature
3
and less organics is required, furthermore, the process is simple
and easy to control.
I. Introduction
II. Experimental Procedure
OMPOUNDS exhibiting simultaneously electric and magnetic
dipoles are available in nature or have been synthesized
is one of the few materials, which
C
BiFeO
(C
tric acid were used as the starting ingredients. Bi
(4 mol% excess) were dissolved in nitric acid solution to obtain
Bi(NO solution. Glycerol was added to Bi(NO solution
with stirring at the temperature of 701C, then stoichiometric
Fe(NO O was added. During the process, the mol ratio
3
sample was synthesis by a sol–gel process using glycerol
). Bi powders, Fe(NO O, glycerol, and ni-
ꢁ 9H
powders
1
in the laboratory. BiFeO
H
3 8
O
3
2
O
3
)
3 3
2
3
exhibits simultaneously ferroelectric (T ꢀ8301C) and antifer-
2 3
O
C
2
romagnetic ordering (T
electric coupling, BiFeO -based systems may be used to develop
3
N
ꢀ3701C). Because of this magneto-
3
)
3
3 3
)
novel applications in the field of radio, television, microwave
and satellite communication, bubble memory device, audio–
3
)
3
ꢁ 9H
2
3
–6
video, and digital recording, etc.
The synthesis procedure
of metal ion to hydroxyl groups in glycerol (M/–OH) was 1:1.5.
With continuous heating at 701C under constant stirring to
evaporate superfluous water, the volume of the solution
decreased and the solution viscosity increased continuously. A
for this material is problematic as it is very difficult to obtain the
pure phase because the temperature stability range of single-
7
,8
3
phase BiFeO is very narrow. As a conventional preparation
technique, solid-state reactions based on oxides and carbonates
of metal components have been used, with thermal treatments
around 8001–8301C, but unreacted Bi O /Bi Fe O was present
gel was formed with evolution of NO gas resulting from
x
decomposition of nitrate ions. Throughout the process, no
signs of precipitation were observed. Then, the sample was re-
moved from the hot plate and heated in an oven at 2201C for
2 h. The resulting mass was slightly ground into a fine powder
and BiFeO precursor was obtained. Finally, the precursor was
3
calcined at 3501–6001C for 2 h in static air to obtain BiFeO
3
powder.
Thermogravimetric (TG) analysis (Diamond TG/DTA,
PerkinElmer Instruments, Waltham, MA) was used to monitor
the decomposition and pyrolysis of the precursor at a heating
rate of 101C/min in static air. Fourier transform infrared spec-
troscopy (FT-IR, Vertex 70, Bruker Optik GmbH, Ettlingen,
Germany) was used to determine the chemical bonding of the
2
3
2
4
9
9
3
and was removed by washing with HNO .
A variety of wet chemical methods were also used to synthe-
size BiFeO . Phase-pure BiFeO can be synthesized at low tem-
perature via a hydrothermal process; however, pressure is
3
3
1
0–12
13
required. The microemulsion technique, ferrioxalate pre-
cursor method, solution combustion method, and citrate
1
4
15
1
method can only obtain nearly phase-pure BiFeO and traces
6
3
of a bismuth-rich secondary phase of silenite type were ob-
served. The sol–gel methods based on ethylene glycol (EG),
1
7,18
1
9–21
some carboxylic acids with and without EG
cessfully to prepare single-phase BiFeO . We successfully syn-
were used suc-
3
2
2
thesized BiFeO
3
by polyvinyl alcohol (PVA) route at 4001C.
We also find an interesting phenomenon; it appears that OH
BiFeO precursor and powders. The phases were identified by
3
powder X-ray diffraction (XRD) using CuKa radiation (Bruker
D8 Advance). Field-emission scanning electron microscopy
(FESEM, Sirion 200, FEI Inc., Eindhoven, the Netherlands)
and transmission electronic microscopy (TEM, Analytical
Transmission Electron Microscope, H-600 STEM/EDX
PV9100, Hitachi, Chiyoda-ku, Tokyo, Japan) were used to ob-
group is favor for the formation of BiFeO and the effect of
3
COOH group is just contrary. We guess that it is possible to
synthesize pure BiFeO with a new complexing agent that has
3
D. Lupascu—contributing editor
3
serve the grain size and the morphology of BiFeO powders.
Raman scattering spectra were measured at room temperature
using a Raman spectrometer (Renishaw RM-1000, Gloucester-
shire, U.K.) with a radiation of Ar laser at 514.5 nm. Magnetic
properties were measured using quantum design physical prop-
erty measurement system (Quantum Design, San Diego, CA).
1
Manuscript No. 28531. Received August 31, 2010; approved February 28, 2011.
This work is supported by the Natural Science Foundation of China under grant
number 10975055.
wAuthor to whom correspondence should be addressed. e-mail: xuyebin@yahoo.com
3
060

September 2011
A Facile Route to the Synthesis of BiFeO at Low Temperature
3
3061
100
98
96
94
92
90
88
86
6
00°C
00°C
400°C
50°C
5
3
precursor
100
200
300
400
500
600
700
Temperature (°C)
1
0
20
30
40
2
50
θ (deg.)
precursors and powders calcined at
60
70
80
Fig. 1. TG curve of BiFeO
3
precursor.
Fig. 3. XRD patterns of BiFeO
3
III. Results and Discussion
Figure 1 shows the TG curve of the BiFeO precursor powder.
various temperatures for 2 h.
3
The weight loss (12.1%) in the temperature range between room
temperature and 5001C could be assigned to dehydration of the
precursor, the decomposition of nitrate and the carbonization
and volatilization of glycerol. No more weight loss was observed
in the temperature range from 5001 to 7001C. The later XRD
3
Figure 3 shows the XRD patterns of the BiFeO precursor
and powders calcined at 3501–6001C for 2 h. The precursor is
XRD amorphous, as is characterized by the broad continuum.
At 3501C, some weak XRD peaks showed up in addition to the
3
continuum, which correspond to reflections from BiFeO . Heat-
patterns show that single-phase BiFO was completely crystal-
ing the precursors to 4001C yields pure rhombohedral BiFeO3
with a perovskite structure, and the XRD patterns are in excel-
lent accord with ICCD file 86-1518. The XRD analysis did not
show any formation of Bi O or Fe O or any other impurity
3
lized into perovskite phase at 4001C. The TG curve shows a
weight loss until 5001C, maybe this is due to a delay of weight
loss, because the sample for XRD analysis was calcined at 4001C
for 2 h, but the sample in TG analysis is heated at 101C/min
without holding.
2
3
2
3
phases of bismuth ferric oxide such as Bi Fe O , Bi Fe O ,
39
2
4
9
24
2
and Bi25FeO40. Increasing the calcination temperature to 5001
and 6001C, the diffraction peaks become stronger and sharper,
reflecting greater crystallization. No other significant changes
are observed and all diffraction lines could be indexed to the
Figure 2 shows the FT-IR spectra obtained from the precur-
sor and prepared BiFeO powders at different temperature. For
3
3
the BiFeO precursor, the broad absorption band in the range of
ꢂ1
3372 cm is assigned to O–H stretching. The bands in the fre-
quency at 1704 and 1633 cm were assigned to the asymmetric
3
rhombohedral structure of BiFeO . Therefore, single-phase
ꢂ1
23,24
BiFeO was completely crystallized into the perovskite phase
3
ꢂ
ꢂ
COO stretching vibrations.
molecules; however, some hydroxyl groups of glycerol molecules
3
can be oxidized to COO by the excess HNO . The bands
There is no COO in glycerol
at a temperature as low as 4001C. The average crystallite sizes of
the synthesized powders are also determined according to the
X-ray line-broadening of the (012) diffraction peak using Scher-
rer’s equation: D 5 0.89l/B cos y, where D is the crystallite size;
l is the X-ray wavelength (0.15406 nm for CuKa); B is the
corrected FWHM of the diffraction peak; and y corresponds to
the diffraction angle. The average crystallite size was about 96 and
338 nm for the powders calcined at 4001 and 6001C, respectively.
ꢂ
ꢂ1
located at around 1385, 1040, and 795 cm indicated the
The absorption features at 443
1
8,21,24
existence of nitrate ions.
and 553 cm are, respectively, attributed to the Fe–O stretching
and bending vibrations, being characteristics of the octahedral
ꢂ1
25,26
FeO groups in the perovskite compounds.
For precursor
6
heated at 4001 and 6001C for 2 h, all the organic peaks are seen
to disappear.
To get further insight on the structural variation of BiFeO
samples, a Raman study was also carried out, as shown in Fig. 4.
3
600°C
600°C
400°C
precursor
3500
400°C
5
00
1000
1500
Wavenumber (cm–1
2000
2500
3000
200
400
600
800
1000
)
Raman Shift (cm–1
)
Fig. 2. FT-IR spectra of BiFeO
3
precursor and powders calcined at
4001 and 6001C.
3
Fig. 4. Raman spectra of BiFeO powders calcined at 4001 and 6001C.

3
062
Journal of the American Ceramic Society—Liu et al.
Vol. 94, No. 9
3
Fig. 6. TEM image of BiFeO precursor calcined at 4001C.
3
0 kOe. With calcination temperature increasing from 4001 to
6
creased, consistent with other report.
001C, corresponding coercivity and magnetization are de-
1
7
Many authors reported the synthesis of BiFeO
method
3
via sol–gel
and the results were listed in Table I. EG, PVA,
and glycerol monomer contain only OH group but not COOH
1
4,16–22
1
7,18,22
group, pure BiFeO
phase BiFeO can also be obtained with tartaric acid and
malic acid. With EG as polymerizing agent, pure BiFeO
3
can be synthesized easily.
Single-
3
1
9
3
20
can be obtained from citrate and maleic precursor, but not
from malonic acid and succinic acid precursors. From Table I,
we can see that OH group is favor for the formation of BiFeO
Fig. 5. FESEM micrographs of BiFeO
a) and 6001C (b) for 2 h.
3
powders calcined at 4001C
19
(
3
and the effect of COOH group is just contrary. It is unclear what
the reason could be.
Glycerol is a triple alcohol and can form complexes with
Eleven fundamental Raman modes can be seen in each spec-
trum. According to the former literature, the peaks at 139, 172,
ꢂ1
30
and 220 cm are the A modes, and the other peaks are related
1
many metal ions. Phase pure BiFeO powders were success-
3
2
7–29
to the E modes of BiFeO molecules.
Our Raman spectra
are in good agreement with that of previously reported
fully prepared at 4001C. This formation temperature is the same
as that in PVA route, but is lower than that in other sol–gel-
3
2
2
17,27–29
data.
17–21
based method.
On the other hand, with increasing calcinations
temperature to 6001C, the intensity of the 139 cm peak in-
Furthermore, no intermediate phases were
ꢂ1
observed. The role of glycerol was attributed to generate a
highly viscous and stable mixture solution, which prohibited
the aggregation of Bi and Fe and favored the formation of
1
creases. The increase in peak intensity of this normal A mode is
indicative of the enhancement in the contribution of the Bi-O1
vibrational mode, which might be caused by lattice distortions
and changed spin–phonon coupling in as-prepared BiFeO
3
BiFeO phase. Besides low formation temperature, another
3
1
7
nanoparticles. Increasing calcinations temperature, the peak
ꢂ1
ꢂ1
0.3
0.2
at 615 cm shift to 605 cm , and the intensity decreases ob-
viously. Maybe it is related to the particle size.
Figure 5 shows the FESEM micrographs of BiFeO powders
4
00
3
calcined at 4001 and 6001C for 2 h. The powders calcined at
4001C are found to be agglomerates of some small particles with
diameters of about 100 nm. On increasing calcinations temper-
ature to 6001C, the particle size is growing larger obviously.
3
Figure 6 represents the typical TEM image of BiFeO powders
6
00
0
0
.1
.0
calcined at 4001C for 2 h. As can be seen, the powder comprises
nanoparticles with an average size about 100 nm. The particle
sizes calculated from the XRD peak widths by Scherrer’s equa-
tion agree with those from TEM and FESEM. The powder
produced is also very agglomerated which could be due to the
small amount of gas being evolved during the decomposition of
the small amount of organics.
–
–
0.1
0.2
–0.3
30000 –20000 –10000
–
0
10000 20000 30000
The magnetic hysteresis loops of BiFeO
001 and 6001C are shown in Fig. 7. Weak ferromagnetism is
observed with corresponding coercivity about H ꢀ732 Oe and
3
powders calcined at
H (oe)
4
c
Fig. 7. Magnetic hysteresis loops of BiFeO powders calcined at 4001
and 6001C. The inset shows an enlarged view of the curve for samples
calcined at 6001C.
3
H
c
ꢀ110 Oe for sample clacined at 4001 and 6001C, respectively.
The magnetization does not saturate even at high fields of

September 2011
A Facile Route to the Synthesis of BiFeO at Low Temperature
3
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3
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1
only 92 g organics is required. For EG method, tartaric
7
3
(
21
19
22
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3
17
19,20
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3
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18
3
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A facile glycerol route was used to synthesize BiFeO
3
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3
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