Materials Transactions, Vol. 55, No. 1 (2014) pp. 147 to 153
© 2013 The Japan Institute of Metals and Materials
Solvothermal Synthesis of Shape-Controlled Perovskite MTiO3
(M = Ba, Sr, and Ca) Particles in H2O/Polyols Mixed Solutions
Takeshi Kimijima+, Kiyoshi Kanie, Masafumi Nakaya and Atsushi Muramatsu
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
Perovskite oxides MTiO3 (M = Ba, Sr and Ca) with various phase, size, and shape were systematically prepared by solvothermal method
in H2O/glycols mixed solutions. Shape control of the BaTiO3 and SrTiO3 particles was achieved by choice of glycols, and anisotropic rodshaped fine BaTiO3 particles with a tetragonal crystal system were selectively synthesized by use of ethylene glycol. On the other hand, cubicand spherical-shaped BaTiO3 particles were also obtained in H2O and H2O/diethylene glycol systems. These BaTiO3 particles had a cubic
crystal system. Meanwhile, concave cubic-shaped CaTiO3 particles with an orthorhombic phase were synthesized. In our method,
triethanolamine­titanium complex was used as the titanium source of MTiO3. Both of the specific adsorption of triethanolamine and solvent
effect of glycols is the competitive factor for the control of final particle size and shape. [doi:10.2320/matertrans.M2013350]
(Received September 10, 2013; Accepted October 24, 2013; Published November 29, 2013)
Keywords: shape control, barium titanate, strontium titanate, calcium titanate, solvothermal synthesis, glycol
1.
Introduction
Perovskite-type alkaline earth titanates (MTiO3: M = Sr,
Ba and Ca) are well known as functional materials with
piezoelectric, ferroelectric, and dielectric properties and
widely used as gas sensors, non-volatile memories, capacitors, microwave devices, and photocatalysts.1­5) For example,
BaTiO3 is used as multilayer capacitor, gate dielectrics,
and IR detector because of its high dielectric constant and
ferroelectric properties.1­3,6) The dielectric property is derived
from its ferroelectric tetragonal crystal structure, and the
property disappeared by phase transition into a paraelectric
cubic crystal structure at ca. 130°C. In addition, crystal size
and shape also affect the crystal phase structures.7­9) On the
other hand, SrTiO3 is one of the most plausible candidates as
high performance photocatalysts for water splitting reaction.10,11) To improve the photocatalytic activity, size and
shape control of the SrTiO3 particles might be a promising
tool because drastic increase in the activity is observed for
size- and shape-controlled TiO2-based photocatalysts with
specific crystal planes.12­14) Further, CaTiO3 has been
investigated for biocompatible and luminescent materials.15,16) Even in this case, size and shape control is an
effective tool to enhance the fluorescent intensity. In this
regards, crystal phase, size, and shape control of these
perovskite oxides particles is one of the quite useful
technique to develop high performance functional materials.
However, most MTiO3 particles are produced by grinding of
the corresponding ceramics prepared by solid phase synthesis, and aggregated inhomogeneous particles with broad size
distribution are only accessible. So far, intensive efforts have
been carried out to synthesize phase-, size-, and/or shapecontrolled MTiO3 particles by hydrothermal,17­19) solvothermal,20,21) and molten salt methods.22) For example, sizecontrolled spherical BaTiO3 nanoparticles with the size of
5­10 nm are prepared via a non-aqueous sol­gel method.20)
Solvothermal methods to obtain cubic-shaped BaTiO3 nanoparticles with the size of 40­90 nm are also reported.21,23)
+
Corresponding author, E-mail: [email protected]
Meanwhile, MTiO3 particles with anisotropic shapes such as
wire and/or rod were synthesized by hydrothermal methods.24­26) However, in these methods, such MTiO3 particles
are obtained, topochemically, by way of intermediates with
the corresponding shapes. Therefore, direct liquid phase
synthesis of phase-, size- and shape-controlled perovskite
particles is still limited.
In our previous studies, we have reported hydrothermal
synthesis of SrTiO3 nanoparticles,27) and the procedure has
been applied to a solvothermal system to obtain the SrTiO3
nanoparticles with cubic-, spherical- and anisotropic flakeshapes.28) In this study, we focused on the shape-control
of MTiO3 (M = Ba and Ca) particles, particularly on the
synthesis of one-dimensional BaTiO3 rods because low
dimensional ferroelectric structures promised to increase the
storage density of future ferroelectric nonvolatile memories.29) As a result, BaTiO3 and CaTiO3 particles controlled in
phase, size, and shape have been successfully obtained via
solvothermal method by use of H2O/glycols mixture as a
solvent. Furthermore, the synthetic conditions of MTiO3
particles were also discussed in detail.
2.
Experimental Procedure
A typical procedure for the preparation of shape-controlled
BaTiO3 nanoparticles by use of H2O/glycols mixed solvent
system is as follows: A Ti4+ precursor solution was prepared
by mixing titanium tetraisopropoxide (TIPO, 28.4 g,
0.10 mol) with triethanolamine (TEOA, 29.8 g, 0.20 mol)
under a dry N2 atmosphere to form a water-stable titanium
triethanolamine (Ti-TEOA) complex at room temperature.
After the resulting pale yellow mixture consisting of the
molar ratio of [TEOA] : [TIPO] = 2 : 1 was kept 1 day at
room temperature in a dry N2 atmosphere, water was added to
make an aqueous solution of 0.50 mol L¹1 in Ti-TEOA. Next,
5.0 mL of the 0.50 mol L¹1 Ti-TEOA aqueous solution was
mixed with the same volume of H2O and/or polyols. As the
polyols, ethylene glycol (EG), diethylene glycol (DEG), and
trimethylene glycol (TMG) were used. Next, Ba(OH)2·8H2O
(1.58 g, 5.0 mmol) was added to the resulting solution under
148
T. Kimijima, K. Kanie, M. Nakaya and A. Muramatsu
stirring to adjust the initial mixing molar ratio of Ba/Ti =
2/1. Then, the gel thus obtained after stirring for 90 min was
placed into a Teflon-lined autoclave (volume: 23 mL) and
aged at 250°C for 3 h. The resulting precipitates were washed
and centrifuged one time with 5.0 vol% acetic acid aqueous
solution and three times with ion-exchange water using a
centrifugator to obtain the BaTiO3 nanoparticles. For the
study of the reaction conditions, some conditions were
altered. By the similar manner for the synthesis of BaTiO3,
CaTiO3 fine particles were prepared by the reaction with
Ca(OH)2. Here, the Ca/Ti mixing molar ratio was adjusted
to 1.2/1. In the CaTiO3 synthesis, gel-intermediate was
not obtained after addition of Ca(OH)2 into the Ti-TEOA
aqueous solution, white-colored suspension was only formed.
The resulting suspension was stirred for 90 min at room
temperature before aging at 200°C for 6 h in an autoclave.
Finally, precipitates formed by the aging were collected and
washed by centrifugation and dried to obtain the CaTiO3
nanoparticles.
Crystal structures of MTiO3 particles were characterized
by X-ray diffractometry (XRD) with a Rigaku Ultima IV
system equipped with a Cu K¡ source at 40 kV and 40 mA.
The particle shape was observed by a Hitachi SU1510
scanning electron microscopy (SEM) and a Hitachi H-7650
transmission electron microscopy (TEM) at 100 kV. Electron
diffraction (ED) measurement and High-Resolution TEM
(HRTEM) observation were carried out by a JEOL JEM3010 system at 300 kV to determine the crystal growth
direction of the nanoparticles. Thermogravimetric (TG)
analysis was performed by a Rigaku Thermoplus TG-DTA
8120 at a heating rate of 10°C·min¹1 under Ar gas flow. The
maximum temperature was 800°C.
Fig. 1 TEM images of BaTiO3 particles obtained at various conditions
in H2O: (a) 140°C, Ba/Ti = 1/1; (b) 250°C, Ba/Ti = 1/1; (c) 140°C,
Ba/Ti = 2/1; (d) 200°C, Ba/Ti = 2/1; (e) 250°C, Ba/Ti = 2/1 (BTO1);
(f ) 250°C, Ba/Ti = 1.5/1.
Table 1
3.
3.1
Results and Discussions
Synthesis of shape-controlled BaTiO3 nanoparticles
in H2O or H2O/polyols mixed solutions
Figure 1 shows TEM images of solid particles obtained
with different Ba/Ti mixing molar ratio under hydrothermal
conditions at 140, 200 and 250°C for 3 h. XRD measurement
revealed that all crystalline solids, exhibited in Fig. 1, could
be assigned as a BaTiO3 phase with a cubic crystal system
(JCPDS No. 074-4539). As shown in Fig. 1(a), formation
of irregular-shaped crystalline particles and amorphous-like
precipitates is observed by aging at 140°C with the Ba/Ti
molar ratio of 1/1. Such behavior is also seen by the aging
at 250°C, and the amorphous-like solids are still remained
(Fig. 1(b)). Here, the reaction conditions were the same as
that for the synthesis of SrTiO3 nanoparticles in our previous
study28) except Ba(OH)2 was used instead of Sr(OH)2 as the
alkaline earth metal source. This means that some modification to obtain BaTiO3 phase as a single phase is essential.
In this regard, initial Ba/Ti molar ratio was altered for the
optimization of the reaction condition. When Ba/Ti molar
ratio was adjusted to 2/1, both of spherical and polygonal
crystalline BaTiO3 particles with 80­100 nm in size are
obtained at 140°C aging (Fig. 1(c)). By the increasing the
aging temperature, BaTiO3 particles with spherical and cubic
shapes are formed at 200°C (Fig. 1(d)), and the cubic-shaped
particles are mainly obtained at 250°C (Fig. 1(e)). Formation
Synthetic conditions of BaTiO3 particles.
Polyols
Amount of polyols/mL
BTO1
®
®
BTO2
EG
0.30
BTO3
EG
0.50
BTO4
EG
1.0
BTO5
EG
1.5
BTO6
EG
2.5
BTO7
EG
5.0
BTO8
DEG
1.5
BTO9
DEG
2.5
BTO10
DEG
5.0
BTO11
BTO12
TMG
TMG
1.5
2.5
BTO13
TMG
5.0
of such spherical and cubic shaped particles is also seen in
the system with the Ba/Ti molar ratio of 1.5/1, however, the
resulting particles have somewhat irregular shape. Here, the
particles shown in Fig. 1(e) are denoted as BTO1, and the
reaction condition was applied to the H2O/polyols system.
Table 1 exhibits the detailed synthetic conditions of the
H2O/polyols system. In this system, total volume of the
mixture was fixed to 10 mL. The particles obtained in various
H2O/polyols system are denoted as BTO2­13. First, the
Solvothermal Synthesis of Shape-Controlled Perovskite MTiO3 (M = Ba, Sr, and Ca) Particles in H2O/Polyols Mixed Solutions
addition amount of EG was changed from 0.30 to 5.0 mL to
investigate the effect of EG on the BaTiO3 synthesis (BTO2­
BTO7). Figure 2 shows the TEM images of the solid
particles synthesized by changing the H2O/EG mixing ratio.
While the cubic shaped particles BTO1 with the average
particle size of 73 nm are obtained in the absence of EG
(Fig. 1(e)), polygonal shaped particles with smaller particle
mean size of 54 nm are formed in the presence of 0.30 mL
of EG (BTO2: Fig. 2(a)). As shown in Figs. 2(b)­2(d),
anisotoropic shape evolution of the particles to form a rod
shape is enhanced by increasing the EG amounts (BTO3­5).
Fig. 2 TEM images of solid particles obtained in H2O/EG mixed
solutions: (a) BTO2; (b) BTO3; (c) BTO4; (d) BTO5; (e) BTO6; (f )
BTO7.
Fig. 3
149
The lengths of short and long axes of the rod-shape particles
BTO5 are 150 and 500­1500 nm, respectively (Fig. 2(d)).
Meanwhile, 50­200 nm sized particles with plate-like shape
are obtained when EG amount is over 2.5 mL (Figs. 2(e) and
2(f )). To determine the crystal structures of the solid particles
thus obtained, XRD measurement was carried out. Figure 3
exhibits the XRD patterns of the particles prepared in various
EG amounts (0, 0.50, 1.5 and 5.0 mL). The XRD patterns
confirmed that BTO1 has a BaTiO3 phase with a cubic
crystal system, and BTO3 exhibits a mixed phase with the
cubic and a tetragonal phase. Meanwhile, BaTiO3 nanoparticles with a tetragonal crystal structure (JCPDS No. 0135283) are formed in a system using 1.5 mL of EG (BTO5).
For BaTiO3 synthesis, crystal phase is influenced by the
particle size due to inner defect and high surface energy.7­9)
The critical particle size of the phase transition from a cubic
to a tetragonal is about 50­100 nm. The size of BTO1 and
BTO2 obtained in H2O and 0.30 mL of EG systems is
smaller than 100 nm, whereas that of BTO5 is much larger
than 100 nm. This is the reason why the phase of BTO1
and BTO2 are cubic and only rod-shaped particles BTO5
have the tetragonal crystal structure (Fig. 3(c)). In contrast,
crystalline peaks of the BaTiO3 phases are not observed
and undefined peaks are only seen in BTO7 (Fig. 3(d), EG:
5.0 mL). Recently, X. Jinag and his coworkers prepared some
metal-glycolates in a solvothermal system,30) and the XRD
patterns of the glycolates are similar to that of BTO7
obtained in the present study. To identify the BTO7 crystal
phase, further analysis by TG measurements was carried out.
Figure 4 shows the TG profiles of BTO5 and BTO7. The
weight loss of 3% for BTO5 with the BaTiO3 phase can
be attributed to desorption and/or decomposition of surface
adsorbed water and organic molecules. On the other hand, the
weight loss for BTO7 is assigned as 16%. Such TG behavior
is also observed for that of the metal-glycolates in the
previous study.30) These results suggest that BTO7 can be
identified as a barium titanium glycolate with a multi-layer
structure. These shape and phase change might result from
a strong chelating ability of EG to the titanium precursors.
In the low ratio region of EG, adsorbed and chelating EG
act as effective shape controller, and anisotoropic rod-shaped
BaTiO3 particles were obtained. Meanwhile, no BaTiO3 was
XRD patterns of products prepared in H2O/EG mixed solution systems: (a) BTO1; (b) BTO3; (c) BTO5; (d) BTO7.
150
T. Kimijima, K. Kanie, M. Nakaya and A. Muramatsu
Fig. 4 TG profiles of particles prepared in H2O/EG mixed solution
systems: (a) BTO5 and (b) BTO7.
Fig. 5 TEM images of BaTiO3 nanoparticles obtained in H2O/DEG or
TMG mixed solutions: (a) BTO8; (b) BTO9; (c) BTO10; (d) BTO11; (e)
BTO12; (f ) BTO13.
obtained when 2.5 mL and more EG was added because
chelating EG inhibit the formation of BaTiO3 and stabilize
the glycolate-complex.
Next, H2O/DEG and H2O/TMG ratios were varied to
investigate the effect of the glycolate species on the BaTiO3
synthesis (Table 1, BTO8­BTO13). Figure 5 exhibits TEM
images of BTO8­BTO13. From the TEM images shown in
Figs. 1(f ), 5(a), 5(b) and 5(c), particle mean size of BTO1,
Fig. 6 HRTEM images (a), (c) and their ED patterns (b), (d) of BaTiO3
nanoparticles: (a), (b) BTO1 and (c), (d) BTO5. The ED patterns of (d)
were taken at the circled area of (c).
BTO8, BTO9 and BTO10 are calculated as 73, 67, 71 and
42 nm, respectively. This result means that the particle mean
size is hardly changed by the addition of DEG in the range
from 0 to 2.5 mL (Figs. 1(f ), 5(a) and 5(b)). The resulting
shape of BTO1, BTO8 and BTO9 are also not influenced
by the change of DEG amount, and BaTiO3 particles with
somewhat cubic shape are obtained. Further increase in the
DEG amount up to 5.0 mL results in decrease in the particle
mean size (Fig. 5(c)). On the other hand, drastic decrease in
the particle mean size is observed in the TMG system. In fact,
the particle mean size of BTO11, BTO12 and BTO13 are 60,
35 and 16 nm, respectively (Figs. 5(d), 5(e) and 5(f )). The
electric constant of water and TMG is 80.3 and 35.0
at 20°C, respectively.31) The solubility becomes smaller as
the dielectric constant values decreases.32) Therefore, such
drastic decrease in the particle mean size might be due to
decrease in the solubility of the particles by increasing
polyols amounts in the present systems.33) The resulting
particle shape became irregular (Fig. 5(f )) from cubic
(Fig. 5(d)) by way of sphere (Fig. 5(e)) by increasing TMG
amount. Meanwhile, XRD measurement of BTO8­BTO13
revealed that all particles have a cubic BaTiO3 phase. Here,
the particle size is smaller than 100 nm. This result is also
good agreement with the previous studies7­9) that BaTiO3
particles smaller than 100 nm in the diameter exhibit a cubic
crystal system.
Next, to investigate the crystal growth mechanism,
HRTEM observation and ED measurement were carried
out. Figure 6 shows the HRTEM images and their ED
patterns of BTO1 and BTO5. For BTO1, the ED spots can
be indexed as the [001] zone axis as shown in Fig. 6(b). This
means that the cubic-shaped particles exhibited in Fig. 6(a)
have {100} faces. On the other hand, in the case of BTO5,
planes of the tetragonal
the ED spots of (002) and ð002Þ
BaTiO3 phase appeared towards parallel to the growing
direction of the rod-shape particle (Fig. 6(d)). Therefore,
shape is controlled to obtain the rod-shape particle through
anisotropic crystal growth along c-axis, possibly because
Solvothermal Synthesis of Shape-Controlled Perovskite MTiO3 (M = Ba, Sr, and Ca) Particles in H2O/Polyols Mixed Solutions
151
Fig. 7 (a), (b) SEM images and (c) XRD patterns of CaTiO3 particles
obtained at 250°C with different Ca/Ti ratios in H2O: (a) Ca/Ti = 1.2/1;
(b) Ca/Ti = 2/1.
Fig. 8 (a), (b) TEM images and (c) XRD patterns of particles obtained in
H2O/polyols mixed solutions: (a) H2O/EG and (b) H2O/DEG. The
amounts of polyols are 5.0 mL.
of the specific adsorption of EG on the planes parallel to
c-axis.34) On the other hand, the shape control to form
nanocube must be due to adsorption of TEOA specifically on
to the {100} planes so that the crystal growth is inhibited
along h100i direction.35) However, adsorption ability of
TEOA was weakened when DEG or TMG was introduced as
a solvent. This is the most plausible reason why the irregular
and sphere-shaped particles are obtained in the presence of
DEG or TMG. Both of the specific adsorption of TEOA and
solvent effect of glycols is the competitive factor for the
control of final particle shape, such as, cube, rod, and sphere.
the H2O/EG system. However, XRD analysis revealed that
these particles might be a calcium titanium glycolate because
similar XRD pattern was observed in the BaTiO3 synthesis
(Fig. 3(d)). Actually, in the CaTiO3 synthesis, the glycolate
phase was formed when addition amount of EG was
decreased to 1.0 mL. Meanwhile, cubic and amorphous-like
particles are synthesized in the H2O/DEG solution system
(Fig. 8(b)). In this case, an orthorhombic CaTiO3 phase is
mainly formed but some another undefined peaks are
observed in the XRD pattern. Therefore, the present H2O/
glycol mixed solution system is not an effective tool for the
size- and shape-control of CaTiO3 particles. Compared with
the other alkaline earth elements Sr and Ba, another phase
such as titanate and glycolate become stable because the
solubility of Ca(OH)2 is very low. Therefore, another method
is needed to control the size and shape of CaTiO3 particles.
Hydrothermal condition might be more suitable in view of
the low solubility of Ca(OH)2 in aqueous media.
3.2
Synthesis of CaTiO3 particles by use of H2O/polyols
mixed solutions
First, to synthesize the pure CaTiO3 particles in the
hydrothermal reaction, synthetic conditions such as Ca/Ti
molar ratios and temperatures were varied. Figures 7(a) and
7(b) show the SEM images of the solid particles obtained at
250°C in Ca/Ti = 1.2/1 and 2/1, respectively. The particles
have a concave cubic-shape in both cases, while particle
mean size in Ca/Ti = 1.2/1 is larger than that in 2/1.
Meanwhile, the particles with almost the same size and shape
were formed in the Ca/Ti = 1.2/1 system at 200°C. On the
other hand, both of the concave cubic and a flake-like shaped
particles were formed in a 1/1 system. From XRD measurement, CaTiO3 particles are obtained in an orthorhombic phase
(JCPDS No. 089-8033) as a single phase in the system
of Ca/Ti = 1.2/1. In contrast, diffraction peaks due to the
formation of Ca(OH)2 (JCPDS No. 004-0733) are observed
when the Ca/Ti is adjusted to 2/1. Undefined crystalline
peaks are seen in the system of Ca/Ti = 1/1. This peak
might result from the flake-shaped particles.
Next, this hydrothermal condition was applied to H2O/
polyols mixed solution systems for the shape control.
Figure 8 shows TEM images and XRD patterns of the solid
particles synthesized in different H2O/glycols mixed solutions. The amounts of polyols were adjusted to 5.0 mL.
As shown in Fig. 8(a), rod-shaped particles were obtained in
3.3
Differences among MTiO3 synthesis in hydrothermal condition
Finally, to get better understanding of the present MTiO3
particle synthesis, we compared the obtained particles of
these three alkaline earth metal titanates under hydrothermal
conditions. The synthesis of BaTiO3 and CaTiO3 particles is
mentioned in the previous section (see Figs. 1 and 7).
Therefore, at the beginning of this section, the reaction
temperature and Sr/Ti ratios in the SrTiO3 synthesis were
varied. Figure 9 shows the TEM images of solid particles
obtained in different conditions. From XRD measurement,
only cubic SrTiO3 phase (JCPDS No. 035-0734) was formed
in all cases. When Sr/Ti = 1/1, cubic-shaped particles are
formed at 140°C, while polygonal shaped particles with 50­
150 nm size are obtained at 250°C (Fig. 9(b)). The 40­
60 nm-sized particles with cubic shape are synthesized at Sr/
Ti = 2/1 (Fig. 9(c)). In the Sr/Ti = 1/1 case, the nucleation
rate might be slower than that in the Sr/Ti = 2/1 case
because the degree of supersaturation is lower. In such low
152
T. Kimijima, K. Kanie, M. Nakaya and A. Muramatsu
Fig. 9 TEM images of SrTiO3 particles obtained under various hydrothermal conditions: (a) 140°C, Sr/Ti = 1/1; (b) 250°C, Sr/Ti = 1/1;
(c) 250°C, Sr/Ti = 2/1.
supersaturation case, the growth reaction is more dominant
than the nucleation reaction. This is the reason why the
particles with irregular polygonal shape and large size
distribution are obtained in the Sr/Ti = 1/1 case. Meanwhile,
the results mean that when M/Ti was adjusted to 1/1, only
SrTiO3 was formed as a single phase in all temperature
ranges. On the other hand, both of crystalline and
amorphous-like particles were obtained in the BaTiO3
synthesis (Figs. 1(a), 1(b)). Further, an undefined phase
was obtained as a by-product in the case of CaTiO3 synthesis
(Fig. 7). When the system with the M/Ti ratio of 2/1, well
crystalline BaTiO3 and SrTiO3 particles were formed at 140­
250°C (Figs. 1(c)­1(e), 9(c)), whereas Ca(OH)2 remained as
the impurity phase in the CaTiO3 case (Fig. 7). Pure CaTiO3
phase were synthesized only at Ca/Ti = 1.2/1 (Fig. 7). The
particle sizes of BaTiO3 and SrTiO3 were 40­80 nm, while
that of CaTiO3 was 1­2 µm. According to the literature,36,37)
a hydrous titanium oxide gel with Ba precursor are formed
at the first stage of BaTiO3 synthesis under hydrothermal
condition. Then, the reaction proceeds in a solution by
supplying Ti ions through a dissolution of the gel. The
driving force for BaTiO3 phase formation is the supersaturation, which is determined by the solubility of BaTiO3
and the concentration of the relevant aqueous species of
barium and titanium. Therefore, amorphous-like gel remained
because of low barium concentrations in our case of Ba/
Ti = 1/1, while crystalline BaTiO3 particles were obtained at
Ba/Ti = 2/1. On the other hand, crystalline SrTiO3 particles
were formed at Sr/Ti = 1/1 because the Sr­Ti­gel might
easily dissolves or the solubility of SrTiO3 might be quite
low compared to that of BaTiO3. Meanwhile, solubility of
Ca(OH)2 is quite low compared to that of Ba(OH)2 and
Sr(OH)2. The solubility of these three hydroxides in water is
4.47, 1.00, 0.170 at 25°C and 17.32, 3.56, 0.122 at 60°C,
respectively.31) Therefore, relatively large particles were
synthesized due to the low concentration of calcium species
in solution, and another phase was easily formed.
a cubic, while rod-shaped particles had a tetragonal phase.
Meanwhile, concave cubic CaTiO3 particles with an
orthorhombic phase were synthesized in H2O. Both of the
specific adsorption of TEOA and solvent effect of glycols
is the competitive factor for the control of final particle size
and shape. This solvothermal method in H2O/glycols would
be a quite effective and promising way for the preparation
of anisotropic shaped some metal oxides particles.
4.
15)
Conclusion
In summary, phase-, size- and shape-controlled perovskite
oxides MTiO3 (M = Sr, Ba and Ca) were successfully
prepared by solvothermal method in H2O/glycols mixed
solutions. Furthermore, anisotropic rod-shaped BaTiO3
particles were prepared in a H2O/EG system. On the other
hand, cubic and spherical BaTiO3 particles were obtained in
H2O and H2O/DEG, respectively. The crystal system of
the cubic- and the spherical-shaped BaTiO3 particles were
Acknowledgments
This work was financially supported by the Grant-in-Aid
for JSPS Fellows 24·9295.
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