Materials Sciences and Applicatio ns, 2010, 1, 91-96
doi:10.4236/msa.2010.12016 Published Online June 2010 (
Copyright © 2010 SciRes. MSA
Chemical Reaction and Crystalline Procedure of
Bismuth Titanate Nanoparticles Derived by
Metalorganic Decomposition Technique
Weiliang Liu1*, Xinqiang Wang2, Dong Tian1, Chenglong Xiao1, Zengjiang Wei1, Shouhua Chen1
1Provincial Key Laboratory of Glass and Ceramics, School of Materials Science and Engineering, Shandong Institute of Light Indus-
try, Jinan, China; 2State Key Laboratory of Crystal Materials, Shandong University, Jinan, China.
Received February 25th, 2010; revised April 24th, 2010; accepted April 27th, 2010.
The homogeneous bismuth titanate single-phase nanoscaled ceramic powders have been prepared by means of meta-
lorganic decomposition. The thermal decomposition/oxidation of the pre-heated precursor, as investigated by differential
thermalgravimetric analysis, X-ray powder diffraction, and environment scanning electron microscope, lead to the
formation of a well-defined orthorhombic bismuth titanate compound. Formation of the layered perovskite-like bismuth
titanate occurs via intermediates with sequential changes in the coordination polyhedron of bismuth. The chemical
reactions of precursor powder in heat treatment process have been investigated further by Raman and Fourier transform
infrared spectra, and the reaction mechanism was tentatively proposed thereafter.
Keywords: Reaction Mechanism, Metalorganic Decomposition, Bismuth Titanate, Nanopowders
1. Introduction
Bismuth titanate (Bi4Ti3O12, BTO) belongs to the family
of ferroelectric materials with layered structures, which
can be written as a general formula of (Bi2O2)2+(Bi2
Ti3O10)2-. The layered structure is constructed by alterna-
tive stacking of a triple layer of TiO6 octahedra (pero-
vskite slab) and a monolayer of (Bi2O2)2+ along the c-axis.
Single crystal BTO has low dielectric permittivity and a
very high Curie temperature (Tc = 675C), which makes
it useful for various applications such as memory ele-
ments, optical displays, and piezoelectric converters of
pyroelectric devices in a wide temperature range from 20
to 600C. BTO ceramics have been used in capacitors,
transducers, sensors, etc. [1,2]. The tuning of electric pro-
perties by compositional modification as well as the size
effect can meet commercial specifications for Curie tem-
perature, conductivity, coercivity, compliance, etc. [3,4].
Although BTO is normally prepared by solid-state re-
action of Bi2O3 and TiO2 at elevated temperatures up to
1100C [5], owing to some inherent limitations of the
process that yields large grain size of product phase, sev-
eral alternate chemical syntheses routes have been pro-
posed. These include coprecipitation, sol-gel, hydro-
thermal and molten salt synthesis [6-9]. Metalorganic
decomposition (MOD) employed in the study offers the
advantages of low calcining temperature, simplifying
process, better homogeneity, stoichiometric composition
control, and low cost. The formation mechanism of the
BTO prepared using MOD method, therefore, was pro-
posed in order to get better understanding of the reaction
2. Experimental
The required amounts of bismuth nitrate [Bi(NO3)3.5H2O]
was dissolved in glacial acetic acid (CH3COOH) by stir-
ring at 60°C up to achieve complete dissolution. Stoich-
iometric tetrabutyl titanate [Ti(OC4H9)4] was slowly dr-
opped into the above solution under constant rate stirring.
Acetylacetone (CH3COCH2COCH3) as reagent was used
to stabilize tetrabutyl titanate. And the solution was di-
luted with 2-methoxyethanol (CH3OCH2CH2OH) to ad-
just viscosity and surface tension. The resultant solution
was stirred at room temperature for 1 h and filtered
whereafter to form the stock solution, which was yellow,
clear, and transparent.
The precursor solution thus obtained was dried in an
oven at 90°C for 10 h, resulting in the formation of a fine
yellowish powder. After ground in an agate, the powder
was annealed at various temperatures between 450 and
750°C. Thermal reactions taking place during the calci-
92 Chemical Reaction and Crystalline Procedure of Bismuth Titanate Nanoparticles Derived
by Metalorganic Decomposition Technique
nations of the powder were analyzed in air by thermo-
gravimetric and differential thermal analysis (TG/DTA,
Netzsch STA 449c). The existing phases in the calcined
samples were studied by X-Ray diffraction (XRD, Ri-
gaku D/MAX-A). Crystallite size of calcined powders
was determined by X-ray line broadening using the
Scherrer equation [10]. The evolution of the powder mor-
phology with the calcination temperature was studied by
an environment scanning electron microscope (ESEM,
Quanta 200). The Raman measurements were performed
in the backscattering geometry using a Ventuno 21 NRS-
1000DT instrument at room temperature to study the
lattice dynamics and structural variety. The infrared (IR)
spectra were measured from 400-4000 cm-1 with a Bruker
Tensor 27 FT-IR spectrometer to monitor the chemical
3. Results and Discussion
3.1 Thermal Analysis
The relative weight loss (44%) and differential thermal
analysis of the pre-heated precursor, as shown in Figure 1,
indicate that heat begins to evolve at about 300°C and the
second weight loss occurs around 600°C. It is seen from
the curve of the DTA in this figure that two exothermic
effects appear at about 350 and 750°C, respectively.
Combined with TGA data, it is obvious that the endo-
thermic effect at about 350°C is due to the decomposition
and decarbonization of organic and inorganic compounds.
It also demonstrates that the weight loss takes place in the
endothermic processing between 270 and 420°C, which is
about 24%. The DTA curve shows the exothermic effect
at about 350°C, which probably also corresponds to the
first nucleation events and the solid-state reaction, and it
will be discussed in XRD data. With an increase in tem-
perature, the second exothermic effect, which appears to
be located at ~ 750°C is also present. Although no pre-
vious thermodynamic data have been found in the litera-
ture, the second exothermic effect may be attributed to the
formation of small agglomerate of pure BTO ceramic
powders, and the crystallization process of BTO is com-
pleted before 750°C. At that temperature the weight loss is
finished. The crystallization process takes place simulta-
neously with the combustion of residual organic products
and/or carbon.
3.2 XRD Study
Diffraction is an appropriate technique when following
the formation of a crystalline solid to obtain qualitative
information about the course of a reaction and phase
identification at each step. This information is the first
step in being able to postulate reaction mechanisms.
The X-ray diffraction studies on the samples calcined at
different temperatures for 5 min are shown in Figure 2.
Figure 1. TG/DTA curves for stock precursors
Figure 2. X-ray diffraction patterns of BTO precursor cal-
cined at various temperatures of 90 (a), 450 (b), 550 (c), 650
(d), and 750°C (e). Peaks: (1) Bi2O3, (2) TiO2 , (3) Bi12TiO20,
and (4) Bi4Ti3O12
The XRD pattern of initial powder confirms the am-
ortphous nature, indicating that the powder is non-crys-
talline. The precursor shows evident crystallization as
the emperatures increases to 450C, and the three strong
peaks correspond to Bi12TiO20 and Bi4Ti3O12, respectively.
In the short temperature interval of 450-550°C the pre-
cursor converts completely into the bismuth titanate
compound (BTO and Bi12TiO20). Between 550 and 750°C
all the amorphous phases react rapidly with the Bi12TiO20
intermediate phase leading to the formation of the BTO
compound. It is also found from the XRD spectra that
BTO powder has orthorhombic phase structure when the
annealing temperature is 750°C. The crystallite sizes of
the powder heated at 750°C for 5 min are determined to be
~ 40 nm from the half-width of the X-ray diffraction peaks
using Scherrer’s equation.
Copyright © 2010 SciRes. MSA
Chemical Reaction and Crystalline Procedure of Bismuth Titanate Nanoparticles Derived 93
by Metalorganic Decomposition Technique
Figure 3. ESEM micrographs of nanocrystalline BTO cal-
cined at 750°C for 5min
where θ is the diffraction angle, λ the average wavelength
of X-ray, k the shape factor, and β is taken as half-
maximum line breadth.
An increase in the grain size of BTO powder is ob-
served as the annealing temperature increased up to 650
°C but decrease remarkably thereafter. Figure 3 shows the
ESEM micrographs of bismuth titanate nanoparticles at
temperature of 750C. The grain sizes estimated from
SEM observations were different from those done by
means of Schereer’s equation. The Scherrer’s equation
assumes that all the crystallites are of the same size, but in
an actual specimen, the size range and distribution affect β.
Additionally, incoherent scattering from domains, distor-
tions in the periodicity in the films, and micro-stress con-
tribute to the line broadening and, hence, errors in the
grain size estimation. Because the X-ray line broadening
yields relative crystallite size, if absolute sizes are nec-
essary then electron microscopy must be used to establish
a basis for comparison.
3.3 Raman Spectra
To further confirm the crystallization procedure of BTO
in the MOD method, the powder precursors calcined at
several temperatures were characterized using a Raman
The Raman data on the powders calcined at 750°C
shown in Figure 4(e) agreed with the published results
[11], even though it is not quite exact for the mode
counting in polycrystalline material due to possible sym-
metry breaking, low peak intensity and overlap of vibra-
tion modes. In accordance with Raman data of Bi4Ti3O12,
BaTiO3, and PbTiO3 [11-13], a shorter bond length of
Ti-O than that of Bi-O, suggests that the Raman phonon
modes of the corresponding higher wavenumbers, such
200 400 600 8001000
223 266
Intensity/arb. units
Figure 4. The evolution of the BTO Raman bands with tem-
perature: (a) 90; (b) 450; (c) 550; (d) 650; and (e) 750°C
as the modes at 610 and 847 cm-1, originated mainly from
the vibrations of atoms inside the TiO6 octahedra. The
eak at 847 cm-1 is attributed to the symmetric Ti-O
stretching vibration, while the 610 cm-1 to asymmetric
one;the 266 and 223 cm-1 modes are ascribed to the
O-Ti-O bending vibration. Although the mode at 223 cm-1
is Raman inactive according to the Oh symmetry of TiO6,
it is often observed because of the distortion of octahedron.
The mode at 326 cm-1 is from a combination of the
stretching and bending vibrations. The two modes at 533
cm-1 and 564 cm-1 correspond to the opposing excursions
of the external apical oxygen atoms of the TiO6 octahedra.
The TiO6 octahedra exhibit considerable distortion at
room temperature so that some phonon modes, e.g., at 326,
533, 610, and 847 cm-1, appear wide and weak, which are
expected to induce ferroelectric anomaly of BTO. The
Raman modes of the corresponding lower wavenumbers,
such as the mode at 117 cm-1, originated mainly from the
vibrations between Bi and O atoms, which can be con-
firmed by the shift to higher wavenumber due to the
modification of a lighter Sm atom at a Bi site with in-
creasing doping concentration [14,15].
In Raman spectra of powders calcined at 450-750°C
for 5 min, Figure 4, a few extra peaks or shoulders not
identified with BTO were detected at 152, 319 and 538
cm-1 at 450°C, and 158, 251, and 326 cm-1 at 550°C. In
the samples annealed at 650°C three broad peaks at 339,
501 and 635 cm-1 were observed.
From the above results, the following can be pointed
Copyright © 2010 SciRes. MSA
94 Chemical Reaction and Crystalline Procedure of Bismuth Titanate Nanoparticles Derived
by Metalorganic Decomposition Technique
out. 1) The sharp increase in the intensity of the 265 cm-1
band and the appearance of a band at 538 cm-1 along with
three other peaks at 152, 319 and 849 cm-1 in the sample
calcined at 450°C, indicated the rearrangement of a bi-
nary Bi2O3-TiO2 intermediate structure before the forma-
tion of BTO phase [16,17]. Such a binary intermediate
phase, according to the X-ray diffraction results, seems
to correspond to the Bi12TiO20 compound, albeit this is
not clearly established. The Raman spectra are in agree-
ment with the data reported in the literature within the
experimental errors [11]. The major lines associated to
crystalline Bi12TiO20 were identified in the sample.
However, it has to emphasize that the data from the lit-
erature was obtained from Raman scattering using single
crystals, and the measurements were performed in pow-
dered polycrystalline samples. This could explain the
large bandwidth and minor frequency-shift of the optical
lines associated to polycrystalline samples. 2) Although
the spectrum for the sample heated at 550°C was similar
to that after 650°C except for the almost disappearance of
the bands at 538 cm-1, but the appearance of a band at
158 and a shoulder at 515 cm-1 indicated the coexistence
of the two Bi12TiO20 and BTO phases, which is in
agreement with the DTA and X-ray diffraction results. 3)
The complete disappearance of all the Raman bands cor-
responding to the intermediate phase and, on the other
hand, the increase in the intensity of the peaks at 266,
533 and 847 cm-1, which are representative of a typical
mixed-layered perovskite structure [17], indicated the
formation of a not well crystallized BTO ternary phase
close to the Bi4Ti3O12 composition.
From the above results, we can suggest that, in a first
step, the formation of Bi12TiO20 particles might be con-
sistent with an Avrami-type nucleation and growth
mechanism [18], in which the particles continuously nu-
cleated three-dimensionally within the amorphous poly-
meric precursor matrix below 550°C. After the nucleus
of crystal appears, the primary particle size gradually
increases from the randomly distributed nuclei with the
increasing temperature. The amount of the intermediate
Bi12TiO20 phase rapidly decreased with the BTO forma-
tion and, finally, crystal growth of BTO by a solid-state
reaction as the heat-treatment temperature increased takes
3.4 FTIR Measurements
The IR spectra of the initial and post-annealed powders of
BTO are shown in Figure 5. After drying at 90°C, the
spectrum is complex due to the existence of lots of organic
compounds. Band at 3500 ~ 3200 cm-1 is a characteristic
group frequency from the stretch vibration of -OH [19].
The stretch -CH2 of located at 2930 cm-1. The broad band
around 1750 cm-1 comes from C = O stretch vibration.
The peaks of 1385, 1024, and 731 cm-1 are the character
4000 3200 2400 1600800
Transmittance/arb. units
Wavenumber/cm -1
Figure 5. FTIR spectra of BTO precursor post-annealed at
temperatures of 90 (a), 550 (b), 650 (c), and 750°C (d) for 5
istic ones of NO3
- group. The band at 1285 cm-1 can be
assigned to bending/stretching vibrations of -COOH. The
band at 1100 cm-1 is the stretching mode of C-O group,
and the broad one around 700 ~ 400 cm-1 originates from
the metal-oxygen (M-O) vibration. After annealing at
450°C, many vibration lines disappear because of the
evaporation of most solvents and decomposition of the
organic ingredient. The strong and characteristic band of
1385 cm-1 is from the nitrate group. The peak at 2336 cm-1
is a characteristic pattern for the -COOH group. The only
feature in spectra of 550, and 650°C heated powders is the
band at around 600 cm-1, originating from M-O bonds.
The IR results indicated that most decomposition could be
achieved by heating above 650°C.
3.5 Reaction Mechanism
In Bi-Ti solution system, Ti(OC4H9)4 reacts easily with
CH3COOH to yield Ti(OC4H9)4-x(CH3COO)x that has a
very slow hydrolysis rate in a strong acidity solution:
Ti(OC4H9)4 + xCH3COOH
Ti(OC4H9)4-x(CH3COO)x + xC4H9OH (1)
On the other hand, H+ of acetic acid easily attacks
alkoxy group (–OC4H9) of Ti(OC4H9)4, which will expe-
dite the hydrolysis reaction:
Copyright © 2010 SciRes. MSA
Chemical Reaction and Crystalline Procedure of Bismuth Titanate Nanoparticles Derived 95
by Metalorganic Decomposition Technique
(–OC4H9) of Ti(OC4H9)4, which
 
 
 (2)
Ti OHTi OCHTi O Ti  (3)
TiO[Ti(OC H)]nOTi
 
 
 
32 32
4932 232493
According to the above-mentioned analyses and the
experimental results, the following reaction scheme is the
most reasonable to describe the decomposition process:
4932 232
 (7)
Bismuth titanate Bi12TiO20 is crystallochemically re-
lated to γ-Bi2O3; these compounds have similar structural
frameworks and almost identical cubic cell parameters
[20]. In view of this fact, formation of Bi12TiO20 in the
Bi2O3-TiO2 system can be considered as a phase transition
from α-Bi2O3 to γ-Bi2O3 initiated by incorporation of a
titanium dioxide admixture into the Bi2O3 structure.
The solid-phase synthesis of Bi4Ti3O12 involves oc-
currence of both rearrangement and transport processes;
thus, formation of Bi4Ti3O12 occurs by the mechanism of
successive rearrangements:
23212 20
Bi OTiOBiTiO (8)
1220243 12
BiTiOTiOBiTi O (9)
This transformation pattern reflects the crystallochem-
ical genesis of the structure in the course of the solid-
phase reaction. The structure formation involves a suc-
cessive increase in the number of the nearest atoms adja-
cent to Bi, with the last, high-temperature stage being
accompanied by a considerably larger change in the bis-
muth coordination number than the first, low-temperature
stage [20].
4. Conclusions
In summary, homogeneous and fine BTO ceramic pow-
ders have been prepared by metalorgainc decomposition
method. Based on TGA/DTA, and XRD results, we con-
clude that the synthesis of the BTO compound takes place
through the formation of an intermediate phase of com-
position Bi12TiO20, which is formed during the heating
between 350 and 550°C. Prolonged heat treatment be-
tween 550 and 750°C promote a rapid consumption by
solid-state reaction of the intermediate phase with the
formation of BTO, without any indication on the forma-
tion of other different phases or segregation of the indi-
vidual metal oxides. These results support the contention
for the metalorganic precursor synthesis method as useful
to prepare ceramics with complex composition such as
those of bismuth titanates. The postulated mechanisms are
further confirmed due to the structural variety as shown in
Raman and FTIR studies.
5. Acknowledgements
This work is supported by the Youth Scientist Fund of
Shandong Province (2007BS04007), the Doctoral Startup
Foundation of Shandong Institute of Light Industry, and
National Natural Science Foundation of China (50772
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