Low-temperature synthesis of nanosized bismuth ferrite by soft chemical route

Article abstract of DOI:10.1111/j.1551-2916.2005.00306.x

The present research describes a simple low-temperature synthesis route of preparing bismuth ferrite nanopowders through soft chemical route using nitrates of Bismuth and Iron. Tartaric acid is used as a template material and nitric acid as an oxidizing agent. The synthesized powders are characterized by X-ray diffractometry, thermogravimetry and differential thermal analysis, infrared spectroscopy, and scanning electron microscopy. The particle size of the powder lies between 3 and 16 nm. In the process, phase pure bismuth ferrite can be obtained at a temperature as low as 400°C, in contrast to 550°C for coprecipitation route. On the other hand, we find that, like solid state reaction route, Pechini's autocombustion method of synthesis generates a lot of impurity phases along with bismuth ferrite.

Full text of DOI:10.1111/j.1551-2916.2005.00306.x

J. Am. Ceram. Soc., 88 [5] 1349–1352 (2005)
DOI: 10.1111/j.1551-2916.2005.00306.x
ournal
J
Low-Temperature Synthesis of Nanosized Bismuth Ferrite by Soft
Chemical Route
Sushmita Ghosh, Subrata Dasgupta,w Amarnath Sen, and Himadri Sekhar Maiti
Central Glass & Ceramic Research Institute, Kolkata 700 032, India
The present research describes a simple low-temperature syn-
thesis route of preparing bismuth ferrite nanopowders through
soft chemical route using nitrates of Bismuth and Iron. Tartaric
acid is used as a template material and nitric acid as an oxidiz-
ing agent. The synthesized powders are characterized by X-ray
diffractometry, thermogravimetry and differential thermal anal-
ysis, infrared spectroscopy, and scanning electron microscopy.
The particle size of the powder lies between 3 and 16 nm. In the
process, phase pure bismuth ferrite can be obtained at a tem-
perature as low as 4001C, in contrast to 5501C for coprecipita-
tion route. On the other hand, we find that, like solid state
reaction route, Pechini’s autocombustion method of synthesis
generates a lot of impurity phases along with bismuth ferrite.
is superior to the age old Pechini’s7 autocombustion method of
synthesis, where the latter failed to produce phase pure BiFeO3.
II. Experimental Procedure
Equimolar amounts (0.01M) of Bi(NO3)3 (3.95 g) and Fe(NO3)3
(2.42 g) dissolved in 2 N HNO3 were taken in a beaker. The
parent solutions were standardized for iron and bismuth8 as de-
scribed elsewhere. Tartaric acid in 1:1 molar ratio (3.0018 g)
with respect to metal nitrates was added to the solution. The
solution was heated under stirring on a hot plate until all the
liquids evaporated out from the solution. The temperature of
the hot plate was then kept in the range of 1501–1601C for 1 h.
This fluffy green powder was then collected and calcined at dif-
ferent temperatures (3001–6001C) for 2 h. The yield was 92%.
The same procedure was repeated with citric acid in place of
tartaric acid and the resultant powder was analyzed.
We also followed Pechini’s method of autocombustion to
make BiFeO3. In Pechini’s method certain hydroxycarboxylic
acids, such as citric acid, form polybasic acid chelates with metal
ions and this chelate can undergo polyesterification when heated
with a polyhydroxy alcohol to form a polymeric glass which
has cations uniformly distributed throughout. Trials have been
made to prepare BiFeO3 with Pechini’s autocombustion method
using various citrate nitrate ratio.
I. Introduction
NE of the very few magnetoelectrics (ferroelectromagnet/
seignetomagnet) materials where there is a coexistence of
O
interrelated electric and magnetic dipole structures within a cer-
tain temperature range is BiFeO3 with perovskite structure.
BiFeO3 is ferroelectric (TcB1083 K) and at the same time, an-
tiferromagnetic (TnB657 K). Although BiFeO3 was discovered
in 1960, its applications in electronic industries were hampered
because of current leakage problems arising out of non-
stoichiometry. Recently, there is a renewed interest in BiFeO3
because of its possible novel applications1–4 in the field of radio,
television, microwave and satellite communication, bubble de-
vices, audio–video and digital recording, and as permanent
magnets. Incidentally, the synthesis of BiFeO3 is plagued with
problems because of the formation of impurity phases. So far
primarily two techniques have been successful in synthesizing
phase pure BiFeO3. In the solid state route5 Bi2O3 and Fe2O3 are
reacted at a temperature in the range of 8001–8301C and unre-
acted Bi2O3/Bi2Fe4O9 phases are removed by washing in HNO3.
The disadvantage of this process lies in the necessity of leaching
the unwanted phases using an acid and effectively providing
coarser powder and also the reproducibility of the process is
quite poor. The other technique is to take recourse to simulta-
neous precipitation/coprecipitation6 where solutions of bismuth
and iron nitrates are treated with ammonium hydroxide to get
hydroxide precipitate. The precipitate needs calcination at a
temperature of 5501–7501C to get phase pure BiFeO3.
The powders were characterized by using X-ray diffraction
(XRD) (PW 1710, Phillips, Spectries Pvt. Ltd., Amello, Nether-
lands). The powder morphology was studied using scanning
electron microscopy (SEM) (Leo 430i, Carl Zeiss, Germany).
Thermogravimetric analysis (TGA) and differential thermal
analysis (DTA) of the powders were carried out with Shimadzu
(TGA-50) analyzer (Kyoto, Japan). IR spectra of the powders
were taken with a Nicolet Model 5PC FTIR (Madison, WI).
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III. Results and Discussion
Figure 1 shows the XRD patterns of the synthesized powder
prepared via tartarate route, heated in air at different temper-
atures. The synthesized powder (green powder) is of amorphous
nature (Fig. 1(a)). After heat treatment BiFeO3 phase begins to
form, and the phase formation is completed at 4001C. The XRD
patterns are in excellent accord with the powder data of JCPDS
Card No. 20–169. The particle size of the powders (Table I) were
calculated using Scherrer’s formula:
In the present communication we report the synthesis of
nanosized magnetoelectric bismuth ferrite by a solution evapo-
ration process at a temperature of 4001C. The process is simple,
energy saving, and cost effective. We also show that this process
0:9l
D ¼
b cos y
where D is the average grain size, l 5 1.5411A (X-ray wave-
length), and b is the width of the diffraction peak at half max-
imum for the diffraction angle 2y.
L. C. Klein—contributing editor
Figure 2 shows the SEM micrographs of the powder. The TG
curve (Fig. 3) of the uncalcined powder depicts a very small
weight loss up to 7001C (0.71%), which is because of the pres-
ence of trapped nitrates (as also confirmed from IR dip (Fig. 4)9
Manuscript No. 11346. Received September 21, 2004; approved December 15, 2004.
Supported by the CSIR Network project CMM 002.
wAuthor to whom correspondence should be addressed. e-mail: sdasgupta@cgcri.res.in
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Vol. 88, No. 5
Fig. 2. Scanning electron microscopy micrograph of the BiFeO3 pow-
der after calcination at 4001C.
100.2
31.4C
0.22%
0.15%
316.1 C
494.9 C
0.45%
699.9 C
0.12%
700
546. 3 C
500 600
− 0.71%
100
99.0
0
200
300
400
Temperature (°C)
Fig. 3. Thermogravimetric analysis curve of green BiFeO3 powder.
presence of two carboxylate and two hydroxyl group with prop-
er orientation to form a polynuclear complex, which breaks on
heating in the presence of concentrated HNO3 leading to the
formation of bismuth ferrite. Similar structure of bismuth tarta-
rate complex10,11 (Fig. 8) shows that nine coordinated12 bismuth
environment and involve bidentate interactions with three alk-
oxide/carboxylate (five-membered ring) and one carboxylate
(four-membered ring) of four different tartarate ligands. Con-
sequently, in the present case bismuth centers are bridged by the
ligands to give coordination polymeric arrays supplemented by
hydrogen bonding between ligands and with water. Such types
of polymeric arrays of bismuth and iron alternately may form
the heterometallic polynuclear polymeric arrays, which on
decomposition in presence of nitric acid give rise to the reac-
tion product.
Fig. 1. X-ray diffractograms of bismuth ferrite powders (a) green (b)
calcined at 4001C (c) calcined at 5001C and (d) calcined at 6001C.
at 1384 cmꢀ1). No evidences of other coordinated or free car-
bonaceous matter in IR spectra indicate the completion of
oxidation of the organics, during the evaporation process. Dif-
ferential thermal analysis (Fig. 5) up to 7001C at a scan rate of
101C/min shows a phase change at 3841C which is the Neel
temperature of BiFeO3.4 DTA of the sample was also carried
out in nitrogen atmosphere and the same result is obtained.
When the synthesis process is repeated with citric acid in place
of tartaric acid, BiFeO3 is formed as a minor phase only (Fig. 6);
the major phases are b-Bi2O3, BiO, Fe2O3, Bi25FeO40, Bi46Fe2O72.
The Pechini’s method7 of auto-ignition also generated a lot of
impurity phases like Bi2O3, Bi2Fe4O9, Bi46Fe2O72 (Fig. 7).
The uniqueness of tartaric acid as a chelating agent in syn-
thesizing BiFeO3 probably resides in the formation of hetero-
metallic polynuclear complexes in the solution, where reacting
metal atoms come in close proximity. This occurs because of the
100
80
60
Ambient CO2
Nitrate
40
20
0
1384cm−1
Table I. Particle Size of the BiFeO3 Powders
Calcination temperature (1C)
Particle size (nm)
Green
300
400
500
600
3.288
3.425
11.013
16.513
16.507
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm−1
Fig. 4. IR spectra of green bismuth ferrite powder.
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6.00
700.0 C
38.3 C
349.2 C
435.8 C
Fig. 8. Nine coordinated Bismuth tartarate showing bidentate interac-
tions with carboxylate groups of four tartarate ligands.
384.0 C
420
−3.00
0
560
140
280
700
Temperature (°C)
Fig. 5. Differential thermal analysis curve of BiFeO3 (calcined at
600oC) powder.
Fig. 9. Bismuth citrate dimeric complex.
The tridentate chelation10 by citrate is available from X-ray
crystallographic reports. The complex of Bismuth (III) with
a tridentate tetra-anionic citrate ligand adopts a well-defined
dimeric arrangement imposed by chelate coordination of the
pendant carboxylate moiety to a neighboring bismuth centre
(Fig. 9). Because of the dimeric nature of the complex (in con-
trast to polymeric arrays for tartaric acid), the possibility of
formation of Bi(III)–Fe(III) heteronuclear arrangement has not
become predominant. This resulted in the formation of impurity
phases via citrate method. This is also true for the Pechini’s
route in the present case. Also it is conceived that during auto-
ignition process, the higher temperature and an excess of car-
bonaceous materials lead to the formation of impurity phases.
Such impurity phases are always observed during the solid-state
synthesis of BiFeO3. However the detailed mechanism under the
reaction conditions must be further studied.
Fig. 6. X-ray diffractogram of BiFeO3 powder synthesized using (a)
tartaric acid calcined at 6001C, (b) citric acid calcined at 6001C, hundred
intensity or next intense peaks are marked.
IV. Conclusion
A simple method has been invented to prepare BiFeO3 nano-
powders using tartaric acid as the chelating agent. Compared
with the conventional solid-state reaction process and coprecip-
itation method, BiFeO3 phase can be formed at a much lower
temperature without formation of any intermediate phase and
therefore a better homogeneity and fine grain size are obtained.
Tartaric acid and nitric acid present in the solution play the key
role for the synthesis of BiFeO3 at a low temperature.
References
1J. D. Bucci, B. K. Robertson, and W. J. James, ‘‘The Precision Determination
of the Lattice Parameters and the Coefficients of Thermal Expansion of BiFeO3,’’
J. Appl. Cryst., 5, 187–91 (1972).
2F. Kubel and H. Schmid, ‘‘Structure of a Ferroelectric and Ferroelastic Mono-
domain Crystal of the Perovskite BiFeO3,’’ Acta Crystallogr., 46, 698–702 (1990).
3V. R. Palkar and R. Pinto, ‘‘BiFeO3 Thin Films: Novel Effects,’’ Pramana J.
Phys., 58 [5, 6] 1003–8 (2002).
4Y. P. Wang, L. Zohu, M. F. Zhang, X. Y. Chen, J. M. Liu, and Z. G. Liu,
‘‘Room-Temperature Saturated Ferroelectric Polarization in BiFeO3 Ceramics
Synthesized by Rapid Liquid Phase Sintering,’’ Appl. Phys. Lett., 84 [10] 1731–3
(2004).
Fig. 7. X-ray diffractogram of BiFeO3 powder synthesized using Pe-
chini’s method calcined at 4001C, hundred intensity or next intense
peaks are marked.

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Vol. 88, No. 5
5G. D. Achenbach, W. J. James, and R. Gerson, ‘‘Preparation of Single-Phase
9I. Nakagawa and J. L. Walter, ‘‘Optically Active Crystal Vibrations of the Al-
kali-Metal Nitrates,’’ J. Chem. Phys., 51 [4] 1389–97 (1969).
Polycrystalline BiFeO3,’’ J. Am. Ceram. Soc., 8, 437 (1967).
6S. Shetty, V. R. Palkar, and R. Pinto, ‘‘Size Effect Study in Magnetoelectric
BiFeO3 System,’’ Pramana J. Phys., 58 [5, 6] 1027–30 (2002).
7M. P. Pechini, ‘‘Method of Preparing Lead and Alkaline Earth Titanates and
Niobates and Coating Method Using the Same to Form a Capacitor’’; U.S. Patent
No. 3330697, July 11, 1967.
10G. G. Brand and N. Burford, ‘‘Coordination Complexes of Bi(III) Involving
Organic Ligands with Pnictogen and Chalcogen Donors’’; pp. 285–357 in Advanc-
es in Inorganic Chemistry, Vol. 50. Elsevier Press, Amsterdam, 2000.
11A. W. Herrmann, E. Herdtweck, K. Wolfgang, and P. Paul, ‘‘Metal Com-
plexes in Biology and Medicine, V. New Bismuth Hydroxycarboxylate Complexes-
Synthesis and Structure of Bismuth (III) Malate Monohydrate and Bismuth (III)
Tartarate Trihydrate,’’ Chem. Ber., 126 [1] 51–6 (1993).
Q6
8A. I. Vogel, ‘‘Determination of Bismuth Using Xylene Orange Indicator and
Determination of Iron Using Dichromate method’’; pp. 442, 309, 310 in A Text
Book of Inorganic Analysis, 3rd edition, Longmans, Green & Co., Ltd., London,
1961.
Q5
12M. Marezio, J. P. Remeiko, and P. D. Dernier, ‘‘The Crystal Chemistry of the
Rare Earth Orthoferrites,’’ Acta Crystallogr., B26, 2008–22 (1970).
&