Chem. Mater. 2010, 22, 3015–3020 3015
DOI:10.1021/cm1004714

Nanosized Tetragonal BaTiO3 Powders Synthesized by a
New Peroxo-Precursor Decomposition Method
Isao Tsuyumoto,* Mitsuru Kobayashi, Tomohide Are, and Naoya Yamazaki
Department of Applied Chemistry, College of Bioscience and Chemistry, Kanazawa Institute of Technology
7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan
Received February 14, 2010. Revised Manuscript Received March 8, 2010

A new peroxo-precursor decomposition method is developed for synthesis of BaTiO3. Peroxopolytitanic acid solution is prepared by reaction between metallic titanium powder and H2O2 aq, andthe amorphous peroxo-precursor is prepared by mixing the peroxo-polytitanic acid with Ba(OH)2 aq.
The reaction time between the metallic titanium powder and H2O2 aq is shortened from 72 to 6 h byincreasing the concentration of H2O2 aq from 30 to 70 wt %. BaTiO3 with crystallite size of
14.7-419.7 nm and tetragonality c/a of 1.0037-1.0090 is obtained by heating the precursor for 1 h at
600-1150 °C in air. BaTiO3 obtained at 650 °C shows a uniform size distribution in the field-emission
scanning electron microscope (FE-SEM) image around 30 nm, and the dielectric constant of 360.
Introduction
Barium titanate (BaTiO3) is an important electroceramic material used for multilayer ceramic capacitors(MLCC), positive temperature coefficient (PTC) thermistors, and electro-optic devices, because it has high dielectric permittivity and ferroelectric properties. BaTiO3
powders with small grain size and high dielectric permittivity are desirable for the applications to the MLCC
because the downsizing of the MLCC is achieved by using
thin ceramic layers with high dielectric permittivity. The
conventional solid state reaction between BaCO3 andTiO2 around 1250 °C has been mainly employed tosynthesize BaTiO3 since the discovery of its ferroelectricity in the 1940s. The solid state reaction between BaCO3
and TiO2 has been reported to occur in three basic stages:
first, formation of a surface layer of BaTiO3 on the outersurface regions of TiO2 by the diffusion of Ba2þ ions into
TiO2; second, formation of Ba2TiO4 by further diffusionof Ba2þ ions and reaction with the prior-formed BaTiO3;
and finally, the reaction between Ba2TiO4 and remaining
TiO2 to form BaTiO3.1-4 Such complex reaction mechanism necessitates repeated calcination and regrinding inlong periods, and the long high temperature processbrings about irregular crystal growth and uncontrolled
particle morphology. Novel processes that allow the
preparation of homegeneous BaTiO3 at relatively low
temperatures are highly desirable to obtain fine particles
for the MLCC applications.
*To whom correspondence should be addressed. E-mail: tsuyu@neptune.
kanazawa-it.ac.jp.

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r 2010 American Chemical Society

In recent years, soft-chemical processes such as thehydrothermal method,5-21 the sol-gel method,22-28
and the precursor decomposition method29-32 havebeen intensively investigated to prepare BaTiO3, and(5) Kubo, T.; Hogiri, M.; Kagata, H.; Nakahira, A. J. Am. Ceram.
Soc. 2009, 92, S172–S176.
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Kageyama, H.; Suyama, Y.; Ohtori, N.; Nagasawa, M. J. Mat. Sci.
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the preparation of nanosized BaTiO3 powders throughsuch processes have been reported by many researchers.5,10,11,22,29,30 Such processes have advantages
over the conventional solid state reactions to prepare
homogeneous and fine powders because nucleation inaqueous solution or amorphous solid matrix, and subsequent crystalline growth by precipitation from solution
or thermal decompostion of solid phase, proceed at lower
temperatures. To ensure the quality of the products, it isessential to mix raw materials equally at microscopic
scale, and the fine raw materials are usually dispersed ina liquid to mix them equally in the conventional solid state
reaction process. In the soft-chemical processes, barium
and titanium are mixed equally at nanometer scale, andthey are appropriate for the preparation of ordinary
particles, as well as of nanosized particles. In general,
the ferroelectric BaTiO3 belongs to the tetragonal perovskite crystal structure, and its ferroelectricity vanishes
because of the phase transition to the cubic phase at hightemperature, that is, the tetragonality enormously contributes to its ferroelectricity. However, superfine BaTiO3
directly precipitated in the hydrothermal processes havebeen reported to show lower tetragonality (expressed by
the c/a ratio of lattice parameters). A number of studies
have been made to attain high tetragonality in hydrothermal synthesis.6-8,13,14 A two-step thermal decomposition method of barium titanyl oxalate has been
proposed to prepare nanosized BaTiO3.29,30 Thermal
decomposition processes using precursors containing
the elements other than Ba, Ti, and O may cause impurities in the product, and thus precursors containing only
Ba, Ti, and O are highly desirable for the synthesis.
We have developed a new technique for preparing
metal oxides from peroxo-poly metallic acid obtainedby direct reaction between metallic powder and hydrogen
peroxide solution. For example, peroxo-polytungstic acidis obtained by vigorous reaction between metallic tungsten powder and hydrogen peroxide solution, and an
amorphous precursor is precipitated by mixing an alkali
solution with the peroxo-polytungstic acid.33-35 Heating
the precursor at 500-700 °C yields alkali tungstatesor tungsten bronzes. Similarly, molybdenum, niobium,
vanadium, and titanium powders react with hydrogen
peroxide, and yield the corresponding peroxo-polymetallic
acids.36-39 However, the reaction of the titanium powder
with the hydrogen peroxide was markedly slow comparedto the other metals, for example, 11 g of tungsten powder(30) Wada, S.; Narahara, M.; Hoshina, T.; Kakemoto, H.; Tsurumi, T.
J. Mat. Sci. 2003, 38, 2655–2660.
(31) Cho, W. S. J. Phys. Chem. Solid 1998, 59, 659–666.
(32) Hsiang, H.; Yen, F. J. Am. Ceram. Soc. 1996, 79, 1053–1060.
(33) Tsuyumoto, I.; Kudo, T. Mater. Res. Bull. 1996, 31, 17–28.
(34) Tsuyumoto, I.; Kudo, T. Sens. Actuators, B 1996, 30, 95–99.
(35) Tsuyumoto, T.; Kishimoto, A.; Kudo, T. Solid State Ionics 1993,
59, 211–216.
(36) Yagi, Y.; Hibino, M.; Kudo, T. J. Electrochem. Soc. 1997, 144,
4208–4212.
(37) Kudo, T.; Sasaki, Y.; Hashimoto, M.; Matsumoto, K. Inorg. Chim.
Acta 1988, 145, 205–209.
(38) Kudo, T.; Okamoto, H.; Matsumoto, K.; Sasaki, Y. Inorg. Chim.
Acta 1986, 111, L27–L28.
(39) Kudo, T. Nature 1984, 312, 537–538.

Tsuyumoto et al.

dissolves into 70 mL of 20 wt % H2O2 aq in 30 min,whereas it takes a few days for 0.1 g of titanium powder todissolve into 100 mL of 30 wt % H2O2 aq. To accelerate
the reaction, it has been proposed to start from alkoxides
or titanium tetrachloride instead of metallic titanium
powder and to use the additives such as ammonia.40-44 Some
researchers have reported the preparation of the titanium
dioxide thin films through such peroxo routes.45,46
In this study, we developed a new synthetic route of
BaTiO3 fine powders from peroxo-polytitanic acid obtained by mixing the titanium powder and the hydrogen
peroxide. We considered that starting from titanium
powder without any additives is appropriate to prepare
pure products and successfully accelerated the reaction byusing more concentrated H2O2 solutions (40-70 wt %).
We present here the synthetic details of the BaTiO3 and its
characterizations using Rietveld refinement of X-ray
diffraction (XRD), field-emission scanning electron microscope (FE-SEM) observation, and dielectric constantmeasurement.
Experimental Section
Synthesis. Metallic Ti powder (0.12 g, 95%, 45 μm particle
size, as received from Wako Pure Chemical Industries, Ltd.,
Osaka, Japan) was dissolved in 100 mL of 30 wt % H2O2
solution (Wako Pure Chemical Industries, Ltd., Osaka, Japan)
at 20 °C with stirring. A yellow transparent solution of peroxopolytitanic acid (denoted as Ti-IPA where IPA stands for
isopolyacid) was obtained in 72 h. After removing insolubles
by filtration, we used the solution for the synthesis. By mixing
the Ti-IPA solution with 100 mL of 28 mmol/L Ba(OH)2
aqueous solution, we obtained an amorphous barium peroxopolytitanate as a white yellow precipitate. After storage for 24 h.
at 20 °C, the precipitate was filtered, rinsed with water and driedat 115 °C. By heating the amorphous barium peroxo-polytitanate
in air at 600, 650, 1000, and 1150 °C, we obtained polycrystalline
barium titanates.
To accelerate the reaction between H2O2 and Ti, the H2O2
solution was concentrated up to 70 wt % by distillation under
diminished pressure using a rotary evaporator at 37 °C. The
concentrated H2O2 solution contained almost the same molar
amount of H2O2 as before the concentration, for example, 38 mL
of 70 wt % H2O2 and 46 mL of 60 wt % H2O2 were preparedfrom 100 mL of 30 wt % H2O2. Polycrystalline barium titanates
were prepared by the same procedure as stated above.
Characterization. The ultraviolet-visible (UV-vis) absorption
spectra of the Ti-IPA solutions were taken using a spectrophotometer (V570, JASCO, Tokyo, Japan), and the time-course of theabsorbance at 400 nm was measured to monitor the reaction rate
between Ti and H2O2 aq. The thermal behavior of the amorphous
precursor was investigated by thermogravimetry (TG) and differential thermal analysis (DTA; DTG-50, Shimadzu, Kyoto, Japan)(40) Tsuyumoto, I.; Nawa, K. J. Mat. Sci. 2008, 43, 985–988.
(41) Tsuyumoto, I.; Nawa, K. Solid State Ionics 2008, 179, 1227–29.
(42) Ichinose, H.; Taira, M.; Furuta, S.; Katsuki, H. J. Am. Ceram. Soc.
2003, 86, 1605–1608.
(43) Tada, M.; Yamashita, Y.; Petrykin, V.; Osada, M.; Yoshida, K.;
Kakihana, M. Chem. Mater. 2002, 14, 2845–2846.
(44) Ichinose, H.; Terasaki, M.; Katsuki, H. J. Ceram. Soc. Jpn. 1996,
104, 715–718.
(45) Wang, Z.; Hu, X. Thin Solid Films 1999, 352, 62–65.
(46) Natarajan, C.; Fukunaga, N.; Nogami, G. Thin Solid Films 1998,
322, 6–8.

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Figure 1. UV-Vis spectra of (a) Ti-IPA solution containing 0.045 mol/Lof Ti and (b) 30 wt % H2O2 solution.

Figure 2. Time courses of Ti-IPA concentration estimated from theabsorbance at 400 nm after mixing Ti powders with H2O2 solutions(30-70 wt %).

at a heating rate of 20 °C/min. The morphologies of the barium
titanates obtained at 650, 1000, and 1150 °C were observed by
FE-SEM (SU-70, Hitachi, Tokyo, Japan) with an accelerating
voltage of 0.7 kV. The XRD patterns of the products were
measured with a diffractometer (XD-D1, Shimadzu, Kyoto,
Japan) using graphite - monochromatized Cu KR radiation (λ =0.15406 nm) at 30 kV and 30 mA. The X-ray profiles were collected
between 2° and 120° of 2θ angles with a step interval of 0.02° and acount time of 1 s/step. The crystalline parameters of the obtained
BaTiO3 were refined by the Rietveld method using the RIETAN2000 program.47 The crystallite sizes of BaTiO3 were determined by

Figure 2 shows the time-courses of Ti-IPA concentration after mixing Ti powders and H2O2 solutions (3070 wt %). The reaction rate was remarkably increased
with increasing the concentration of H2O2 solution. The
reaction was completed in 6 h when 70 wt % H2O2 wasused, while a few days were needed to complete thereaction with 30 wt % H2O2. The reaction rate curves in
Figure 2 were well fitted with a third reaction, whose rateequation is expressed by

p ¼ 180Kλ=πX

ð1Þ

where p is the crystallite size, K is the Scherrer constant (0.9), λ is the
wavelength of X-ray, and X is a peak profile parameter, theLorentzian Scherrer broadening obtained in the Rietveld refinement. The Ba/Ti molar ratios of the specimens were determined by
X-ray fluorescence spectrometry (XRF-1700, Shimadzu, Kyoto,
Japan) using the fundamental parameter (FP) method. Dielectric
constant measurement using the complex impedance plot (50 Hz5 MHz) was performed on the pellet (5 mm  8 mm  0.54 mm)of the obtained BaTiO3 fabricated by monoaxial pressing at
200 MPa. The capacitance C of the pellet was calculated from therelationship,
2πfRC ¼ 1
where f is the frequency at the top of semicircle and R is the diameterof the semicircle.

Results and Discussion
Preparation and Properties of Ti-IPA Solution. The
UV-vis spectrum of the Ti-IPA solution (0.045 mol/L
as to Ti) is shown in Figure1 along with that of 30 wt %H2O2 solution. The Ti-IPA solution showed a wide andstrong absorption band extending from the UV to the Vis
region and decaying at around 500 nm, whereas the H2O2
solution showed a strong absorption band only in the UV
region. The molar extinction coefficient (ε) of Ti-IPA
solution at 400 nm was estimated as 6.11 104 cm2 mol-1.
The absorption in the range of 320-500 nm is considered
to be due to electronic transitions in the titanium complex
ion with a peroxo group as a ligand. We observed theabsorbance at 400 nm to monitor the concentration of the
Ti-IPA during the reaction between Ti and H2O2 because
H2O2 showed no absorption at 400 nm.
(47) Izumi, F.; Ikeda, T. Mater. Sci. Forum 2000, 321-324, 198–205.

d½Ti-IPA=dt ¼ kmTi ½H2 O2 2ð2Þ

where mTi is a molar amount of Ti dispersed in 1 L of thesolution. The rate coefficient k was estimated as 1.4 
10-7 L2 mol-2 s-1. The reaction between H2O2 and Ti issimply expressed byTi þ 2H2 O2 f Ti-IPA

ð3Þ

This may suggest that the Ti-IPA ion contains two peroxo
groups or H2O2 molecules as ligands.
The reaction rate of this peroxo-route was substantially
improved by using the concentrated H2O2 solutions. It isalso expected that the peroxo-route will be applied toindustrial manufacture of photocatalyst thin films because aqueous solutions containing titanium is especially
useful for preparing TiO2 thin films. Additionally, heating the mixture of Ti and H2O2 above 50 °C makes thesolution turbid because of decomposition of the titanium
complex, and thus the reaction cannot be accelerated byheating.
The Ti-IPA solution formed a yellow gelatinous precipitate by drying at room temperature. In TG measurement, the gelatinous precipitate showed weight loss by
95.8% in the range of room temperature to 210 °C andformed a yellow amorphous powder. The amorphous
powder crystallized into the anatase TiO2 around 330 °C
and into the rutile TiO2 around 700 °C.
Preparation of BaTiO3 and Its Characterizations. Figure 3
shows the TG and DTA curves for the amorphous barium
peroxo-polytitanate precipitated by mixing the Ti-IPA solution with Ba(OH)2 aqueous solution (see Experimental
Section). A broad endothermic peak accompanied by gradual weight decrease was observed from room temperature
to around 160 °C because of desorption of hydrated water.
An exothermic peak accompanied by a steep weight decrease around 594 °C indicates that the amorphous salt

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Tsuyumoto et al.
Table 1. Refined Crystallographic Data for BaTiO3 Obtained by Heating
the Precursor at 600-1150°C
Tetragonal; Space Group; P4mm (99) Z = 1
atom

crystallizes around 594 °C accompanied by the decomposition of peroxo groups. The composition of the amorphous barium peroxo-polytitanate is estimated as BaTiO2.65(O2)0.35 3 nH2O from the steep weight decrease by 2.4%.
The XRD patterns for the samples heated in air for 1 h
at 600, 650, 1000, and 1150 °C are shown in Figure 4 alongwith that for the as-precipitated sample. The XRD patterns for the samples obtained by heating over 600 °C
were coincident with those of the conventional tetragonal
BaTiO3 (PDF-050626), whereas the as-precipitated sample was amorphous. The crystallinity of the BaTiO3 wasincreased from 600 to 650 °C, showing little change above
650 °C. The structural parameters for BaTiO3 obtained
from the Rietveld refinement are summarized in Table 1.
All the XRD data were well refined with the space group
P4mm, and showed the tetragonality (c/a > 1). It is
important to note that BaTiO3 obtained by heating at
rather low temperature 600 °C also showed the tetragonality, c/a = 1.0037, while the low-temperature synthesisof BaTiO3 in most of the earlier reports generally yielded
the cubic phase. The crystallite size of BaTiO3 determinedfrom the peak profile parameters was increased almost
two times from 14.7 to 25.9 nm between 600 and 650 °C.
It was gradually increased from 25.9 to 48.3 nm up to

atomic position

occupancy

Ba
Ti
O(1)
O(2)

600 °C, a = 4.0148(93) c = 4.0297(99)c/a = 1.0037 Crystallite Size: 14.7 nm
1a (0, 0, z)
z: 0.01b (1/2,1/2, z)
z: 0.464(4)1b (1/2,1/2, z)
z: -0.068(18)2c (1/2, 0, z)
z: 0.543(23)

0.99
1.0
1.0
1.0

Ba
Ti
O(1)
O(2)

650 °C, a = 3.9998(67) c = 4.0192(70)c/a = 1.0049 Crystallite Size: 25.9 nm
1a (0, 0, z)
z: 0.01b (1/2,1/2, z)
z: 0.514(15)1b (1/2,1/2, z)
z: -0.058(9)2c (1/2, 0, z)
z: 0.512(85)

0.99
1.0
1.0
1.0

Ba
Ti
O(1)
O(2)

1000 °C, a = 3.9970(28) c = 4.0211(28)c/a = 1.0060 Crystallite Size:48.3 nm
1a (0, 0, z)
z: 0.01b (1/2,1/2, z)
z:0.493(4)1b (1/2,1/2, z)
z:-0.032(7)2c (1/2, 0, z)
z:0.519(23)

0.99
1.0
1.0
1.0

Ba
Ti
O(1)
O(2)

1150 °C, a = 3.9942(23) c = 4.0302(23)c/a = 1.0090 Crystallite Size: 419.7 nm
1a (0, 0, z)
z: 0.01b (1/2,1/2, z)
z: 0.526(3)1b (1/2,1/2, z)
z: 0.041(9)2c (1/2, 0, z)
z: 0.534(10)

0.99
1.0
1.0
1.0

Figure 3. TG and DTA curves of the amorphous precursor, barium
peroxo-polytitanate, at heating rate 20 °C/min in air.

Figure 4. XRD patterns of the as-prepared precipitate and of BaTiO3
samples obtained by heating the precipitate in air for 1 h. at 600-1150 °C.

site1000 °C and sharply increased to 419.7 nm at 1150 °C.
This behavior suggests that the crystal growth of BaTiO3
mainly occurs by precipitation from the amorphous
phase around crystal nucleus at 1000 °C or below, andthat the crystal growth by fusion of fine particles proceeds
around 1150 °C. The tetragonality (c/a) was increased
from 1.0037 to 1.0090 with increasing temperature, suggesting that it can be controlled by changing the heating
temperature. The quantitative X-ray fluorescence analysis indicated that the Ba/Ti ratios were 0.99, and thus theoccupancies of Ba (1a site) were fixed to 0.99 in the
Rietveld refinement.
The FE-SEM images of the BaTiO3 samples obtainedby heating the precipitate in air for 1 h at 650, 1000, and1150 °C are shown in Figure 5a, 5b, and 5c, respectively.
The BaTiO3 sample obtained at 650 °C showed a uniform
particle size distribution around 30 nm, and this wasconsistent with the crystallite size estimated from the
XRD pattern. The sample obtained at 1000 °C consistedof a small number of larger particles in the range 100200 nm and a large number of smaller particles around
50 nm. This indicates that the crystalline growth proceeds
more effectively at 1000 °C than at 650 °C, and that a
portion of particles fused to form larger particles partly
by solid state reaction. The agglomerates of larger particles
were observed in the BaTiO3 sample obtained at 1150 °C.
Around this temperature, the product is mostly formed
through the similar process as the conventional solid state
reaction, and the morphology of the product became
similar to that of the conventional process.
Figure 6 shows the complex impedance plots of thepellets of BaTiO3 obtained at 650, 1000, and 1150 °C.

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Figure 6. Complex impedance plots of the pellets of BaTiO3 obtained at
650, 1000, and 1150 °C. The frequencies at the top of semicircles areindicated by arrows.

Figure 5. FE-SEM images of BaTiO3 samples obtained by heating the
precipitate in air for 1 h at (a) 650, (b) 1000, and (c) 1150 °C.

The dielectric constants of the pellets obtained at 650,
1000, and 1150 °C were estimated at 360, 1160, and 2990.
The dielectric loss tangents of the pellets obtained at
650, 1000, and 1150 °C were 0.26, 0.30, and 0.30 at
100 kHz; and 0.08, 0.13, and 0.17 at 1 MHz, respectively.
The BaTiO3 particles around 25.9 nm size showed thedielectric constant of 360, and the dielectric constantincreased with increasing heating temperature. The dielectric constants were closely correlated with the crystallite size and the tetragonality c/a. Our results confirmed that it is essential to maintain the tetragonality
to obtain nanosized BaTiO3 with high dielectric constants.

The hydrothermal syntheses in earlier reports havemostly provided cubic BaTiO3 when the processing
temperature was below 1000 °C12 or the particle size
was below 190 nm,20 except for a few reports indicating
tetragonal BaTiO3 with c/a = 1.0078 prepared at 523 K5
and with c/a = 1.0078, particle size of 90 nm preparedat 240 °C.17 The oxalate decomposition methods andthe sol-gel method have also provided cubic BaTiO3
when the heating temperature was below 800 °C.25,29,32
Vivekanandan and Kutty reported that the roomtemperature stabilization of cubic BaTiO3 prepared by
the hydrothermal method was due to the presence ofresidual hydroxyl ions in the lattice and compensating
cation vacancies.48 They indicated that, though thehydroxyl ions were removed by heating at 900 °C, thecubic structure was retained up to 1000 °C because of thelattice strain due to the presence of the compensating
cation vacancies. In contrast, by the present peroxo
decomposition method, the rather high tetragonality(c/a = 1.0037) was achieved for the small crystallite size
14.7 nm at the preparation temperature 600 °C. This isprobably because the hydroxyl ions and the cation vacancies are not involved in the amorphous peroxo-precursor.
It can be said this peroxo-precursor decomposition
method is appropriate to prepare nanosized BaTiO3
particles with the tetragonality. Furthermore, this method
can be extended to the preparation of the other titanium
complex oxides such as SrTiO3, BaxSr1-xTiO3, CaTiO3,
Bi0.5Na0.5TiO3 by modification of the agents. We expect
the peroxo-precursor will be a more commonly usedprecursor like the other precursors such as oxalate andcitrate.
Conclusions
Ti-IPA solution was prepared by mixing metallic titanium powder and H2O2 aq. The preparation time of the
Ti-IPA was remarkably reduced from 72 to 6 h by increasing the concentration of H2O2 aq from 30 to 70 wt %.
BaTiO3 was obtained by heating the amorphous precursor, barium peroxo-polytitanate, at 600-1150 °C, which
was precipitated by mixing Ti-IPA solution with Ba(OH)2
aq. The crystallite size and the tetragonality c/a were(48) Vivekanandan, R.; Kutty, T. R. N. Powder Technol. 1989, 57, 181–
192.

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Chem. Mater., Vol. 22, No. 9, 2010

increased from 14.7 to 419.7 nm and from 1.0037 to
1.0090, respectively, by increasing the temperature. The
crystallite size of BaTiO3 obtained at 650 °C was 25.9 nm
from XRD analysis, and the size distribution was homogeneous around 30 nm in the FE-SEM image. The tetra-

Tsuyumoto et al.

gonality c/a and the dielectric constant of BaTiO3
obtained at 650 °C were 1.0049 and 360, respectively.
Our study demonstrates the high potential of peroxoprecursor decomposition methods for the preparation ofnanosized titanium complex oxides.