Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
Structure and Morphology of Nanocrystalline BZT
Powders Prepared Using Hydrothermal Method
M. M. Ismaila, b, *, Sabah. M. Alib, Z. S. Ahmedc and Wan. Q. Cao
a,
Abstract
The nanocrystalline of BaZrxTi1-xO3 (BZT) (where x= 0, 0.001 and 0.008)
powders have been prepared by hydrothermal method at 150oC for 2h using as
prepared titanium tetraclouride, zirconium oxyclouride and barium hydroxide as
starting materials. They were investigated by x-ray diffraction XRD, transmission
electron microscopy TEM, selection area electron diffraction SAED and high
resolution transmission electron diffraction HRTEM. The BaTiO3 (BT)
nanocrystals have a cubic perovskite structure and they convert to tetragonal
perovskite after annealing at temperature 700oC while BZT convert it at higher than
700oC as revealed by XRD. It is found that the increased in Zr content caused a
decreased in tetragonallity factor. The morphology of BT powders showed a star
shape and dendrites pattern, not very smooth surfaces and non uniform in contrast
while the dendrites pattern is absence in BZT as a result of TEM. There is a high
contract variation in the TEM images of BT and BZT which indicates the presence
of strains inside the lattice. The SAED results indicate a perfect crystal structure
and HRTEM images revealed the presence BZT powders that showed small
nucleated islands at the edges of the faceted particles of the prepared BT.
Keywords: Nanocrystalline, BZT, Hydrothermal
a
School of Physics and Electronic, Hubei University, Wuhan 430062, China
School of Applied Science, University of Technology, Baghdad, Iraq
c
Ministry of Science and Technology, Baghdad, Iraq
b
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
those of mixing oxide synthesis due to
finer scale of mixing at relatively low
temperatures. In hydrothermal method,
most of researchers have used alkali
metal hydroxides namely KOH or
NaOH as mineralized. The usage of
aqueous ammonia instead of NaOH or
KOH in hydrothermal process will get
many
advantageous.
Aqueous
ammonia does not have been a
tendency to get incorporated into the
oxide matrix and any residual
ammonia entrained in BT powders can
be easily driven off during the
powders at 100oC[10].
In the present work, we report on a
hydrothermal method to prepare
nanocrystalline
BaTiO3
(BT),
BaZr0.001Ti0.999O3
(BZT1)
and
BaZr0.008Ti0.992O3 (BZT2) powders
and discuss the tetragonality, structural
and morphology of obtained powders.
Introduction
Tetragonal BaTiO3 has excellent
dielectric properties, which makes it
the most important ferroelectric
material used in the manufacture of
thermistors, ceramic capacitor and
especially
multi-layer
ceramic
capacitors (MLCCs)[1].
Substitution of Ti4+ (atomic weight of
49.9, ionic radius of 0.0745 nm) with
Zr4+ (atomic weight of 91.2, ionic
radius of 0.086 nm) exhibits several
interesting features in the dielectric
behavior for BT ceramic. When the Zr
content is less than 10%, the BZT
ceramics show normal ferroelectric
behavior and dielectric anomalies
corresponding to cubic to tetragonal
(Tc), tetragonal to orthorhombic (T2)
and orthorhombic to rhombohedra
(T3) phase transition [2]. This lead
free relaxor material (BZT) presents a
great interest both for applications in
the field of environmental protection
and for fundamental studies.
The conventional method involves
repeated milling and calcinations
(>1200 oC) of BaCO3 and TiO2
powders. This method, however,
results in the formation of nonequimolar barium titanate, such as
Ba2TiO4, BaTi2O5 and BaTi4O9,
which often lead to a compositional
inhomogeniety [3]. Recently, wet
chemical technologies such as the solgel method[4], oxalate method [5, 6]
and hydrothermal method [7, 8, 9]
have been replaced the classical solid
state reaction for the synthesis of BT.
Wet chemical methods have led to
homogeneous, phase pure BT with
comparatively finer particle size than
Experimental
Appropriate
amounts
of
Ba(OH)2.8H2O (98%) and TiCl4
(99%) were weighted and used as
precursor. The dilution procedure
consists of adding the concentration
TiCl4 slowly to the distilled water,
which is kept close to freezing
temperature (~5oC) by water bath,
under the constant stirring conditions.
The result is TiOCl2, which needs to
be used immediately as its shelf life is
only a few hours at room temperature.
Therefore, TiOCl2 is kept in water
bath at temperature ~5oC. The result is
mixed with ZrOCl2 solution. Reactive
gels were precipitated by the dropping
of aqueous ammonia solution to
TiOCl2 and ZrOCl2 solution.
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
The gels were washed from free of
chloride ions and were mixed with
0.6M Ba(OH)2 solution with vigorous
stirrer. The molar ratio of Ba/(Ti+Zr)
and ph are kept at 1.6 and 13
respectively.
The hydrothermal reaction was carried
out in Teflon-lined stainless steel
autoclave and the degree of fill was 80
%. The sealed vessel was heated to
150oC for 2h. After cooling dawn to
room temperature, the resultant
precipitated was washed with distilled
water for several times and finally
dried at 60oC for 24h.Crystal structure
of the produced particles was analyzed
at room temperature using XRD
(D/Max-RB Model). The powder
morphology was performed by TEM
(JEM-100SX NEC).
cubic BT, BZT and BZT2 with lattice
constant 4.0189, 4.021 and 4.0225Ao
respectively. Because of radius of Zr is
lager than Ti, the increasing of lattice
constant with increase of Zr content is
shown. It is known from the literature
that BT is a stable tetragonal phase at
room
temperature
with
lattice
o
constants a = 3.98A and c = 4.02Ao.
To discuss the expanding of lattice
constants for BT and BZT, it is
important to study the reasons of
suppression of tetragonality phase.
The different between cubic and
tetragonal phase of BT is a Brage
angle at 45o on XRD pattern,
therefore, it is better to study the
limited range of XRD especially
between 44 and 46o. This region of the
diffraction pattern is characteristic of
the tetragonal versus cubic from BT.
Fig. 3 shows that the XRD pattern of
as prepared BT and BZT powders at
limited range from 44.6 to 46o with
different annealing temperature (500,
700 and 1000oC). it is found the
splitting of the (200) peak with the
lower angle shoulder indexed at (002)
when annealing temperature at 700oC
is observed in BT as shown in Fig. 3a
while in BZT the splitting is taken
place at higher than 700oC as shown in
Fig. 3b and c. In the cubic form, this
peak remains unsplit. It is apparent
from the Fig.3, annealing temperature
at 700oC expels some defects which
incorporated inside the lattice, and
therefore the lattice constant becomes
a smaller. At 1000oC, all the defects
were removed and the lattice constant
(a) of BT becomes smaller and close
with standard tetragonal BT.
Results and Discussion
XRD results
Fig.1 shows that the XRD pattern
of the BZT using TiO2, ZrOCl2.8H2O
and Ba(OH)2.8H2O at 150oC for 2h
which hydrothermally treated. It is
found the BaTiO3 (BT) and BaZrO3
(BZ) was formed while the BZT does
not form and there are some peaks
refer to TiO2. It is likely the reason of
this result is that the particle size of
raw materials is not fine, especially
TiO2, so it is better to use a fine TiO2.
Fig. 2 shows the XRD pattern of BT.
BZT1 and BZT2 using TiO2 and ZrO2
gels with Ba(OH)2.8H2O using hydrothermal method at 150oC for 2h. This
result indicates the addition of Zr is
forming a stable solid solution with
BT lattice. The XRD pattern is fit well
with the peak positions of standard
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
Fig. 3 b and c show the BZT1 and
BZT2 have the same behavior of BT,
in other words, at a temperature higher
than 700oC, the peak of (200) splits
and phase transition was observed.
The diffuse of Zr in BT was caused the
retarding of appearance the tetragonal
phase because of the BZT need a
higher temperature to form in compare
with the formation of BT so BZT
contains more defects than BT.
Fig. 4 shows the lattice constants of as
prepared BT, BZT1 and BZT2
powders as a function of annealing
temperature. The lattice constants
were calculated from XRD results. It
is found the lattice constant (a)
decreased with an increase of
annealing temperature particularly
decreased rapidly at 500oC for BT
while in BZT1 and BZT2 this happen
after 700oC. The annealed BZT
powders up to 1000oC enable BZT
unit cell to expel all the defects which
incorporating inside it, so that the
distortion of unit cell taken place and
tetragonal phase was observed.
Fig. 5 shows the tetragonallity factor
(c/a) of BT, BZT1 and BZT2 powders
with annealing temperature. It can be
seen the tetragonallity factor increases
with annealing temperature and
decreases with increased of Zr content
as shown in Fig. 6.
many of tiny particles which tend to
form a star and dendrites forms.
Fig. 8b shows the SAED pattern
recorded from Fig. 8a, which
demonstrates good crystallinity comes
from
the
regular
spots
and
coordination.
Fig. 9b depicts the HRTEM image
taken from Fig. 9a. It is shown the
different variations of HRTEM
contract indicate the existence of high
strain in particles. The large strains are
indicated by a contract variation across
the particle and this agreed with the
results of Li et al [11]. The lattice
fringes of HRTEM image was
examined to be 2.84 nm, which close
to the (110) lattice spacing of the cubic
BT. It is also found there is a gradual
contract from bright in the edge of
particle to dark inside it which
indicates a gradual strain inside the
lattice. In addition, the surrounding
edge is not very smooth, and some of
surface steps are observed. The
HRTEM images also revealed the
presence BT powders showed a small
nucleated island at the edges of the
faceted particles
The particle size and morphology of as
prepared BZT2 powders synthesized at
150oC for 2h using hydrothermal
method are shown in Fig 10 a and b.
The particles have a mixture's shape
(spherical and cubes with truncated
edge) with the average size about 150
nm. It can be seen there is absence of a
dendrites shape in BZT powders
compared with the BT powders. This
can be ascribed to the effect of adding
Zr+4 to BT, which make expand of
lattice constants of it.
TEM results
The TEM images of as prepared BT
powders synthesized at 150oC for 2h
using hydrothermal method was
demonstrated in Fig. 7. Fig. 7 revealed
the spherical aggregates composed of
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
The SAED pattern taken from the Fig.
11a is shown in Fig. 11b, which reflect
the regular spot and good crystallinity
of BZT.
Fig. 12 (b) shows the HRTEM image
taken from Fig. 12 (a) of as prepared
BZT2 powders. There is a contract
variation which indicates the existence
of strain inside the particles. The
lattice fringes is close to the (110)
lattice spacing of the cubic BZT.
References:
[1] Lee J. H., Nersisyan H. H., H.H.
Lee and Won C. W., “Structural
change of Hydrothermal BaTiO3
powders” J. Mater. Sci., 39, 1397,
2004.
[2] Moura F., Simoes A. Z., B.
Stojanovic D., Zagheta M. A., E.
Longo and Varela J. A.,
“Dielectric and Ferroelectric
Characteristics of BZT Ceramics
prepared from Mixed Oxide
Method” J. Alloys compound,
462, 129, 2008.
Conclusion
Fine crystalline barium zrogonate
titanate BaZrxTi1-xO3 powders (where
x=0, 0.001 and 0.008) were
hydrothermally synthesized from
mixing TiO2 and ZrO2 gels with
aqueous Ba(OH)2 at 150oC for 2h. It is
found that the expanded of lattice
constant in BT, BZT1 and BZT2 due
to existence of defects inside the
lattice. Increase in Zr content, the
tetragonality factor (c/a) decreased.
Annealing powders shows that the
phase transition was occurred, for BT
at 700oC and for BZT higher than
700oC according to XRD results. The
dendrites pattern is shown in TEM
image of BT but it is not clear in BZT
image. It is shown the different
variations of HRTEM contract indicate
the existence of high strain inside the
lattice. Lattice fringes in HRTEM
images
revealed
that
the
nanocrystalline BT and BZT have a
uniform and perfect crystal structure
with the existence of strains inside the
lattice. The surrounding edges of these
particles are not very smooth and some
surface steps are observed.
[3] Beauger A., Mutin J. C. and
Niepce J. C., “Synthesis Reaction
of Metatitanate BaTiO3” J. Mater.
Sci., 18, 3543, 1983.
[4] Pfaff G., “Sol-Gel Synthesis of
Barium Titante Powders of
Various Compositions” J. Mater.
Chem., 2, 591, 1992.
[5] Sven Van Gijp, Louis Winnubst
and Henk Verweij, “Anoxalate
Preoxide Complex used in the
Preparation of Doped Barium
Titanate” J. Mater. Chem., 8,
1251, 1998.
[6] Bera J., and Savkar D., “Formation
BaTiO3 from Barium Oxalate and
TiO2” J. Electrocaerm., 11, 131,
2003.
[7] Verekanandan R., Philip S. and
Kutty T. R. N., “Hydrothermal
Preparation of Ba(Ti, Zr)O3 Fine
Powders” Mater. Res. Bull., 22,
99, 1986.
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
[8] Yonggang Wang, Gang Xu, Linlin
Yang, Zhaohui Ren, Xiao Wei,
Wenjian Weng, Piyi Du, Ge Shen
and Gaorong Han, “Hydrothermal
Synthesis of Single Crystal
BaTiO3 Dendrites” Mater. Lett.,
63, 239, 2009.
[9] Changhua An, Chunying Liu,
Shutao Wang and Yunqi Liu,
“Generalized
Large
Scale
Synthesis of MTiO3 (M=Ba, Sr,
Pb) Nanocrystals” Mater. Res.
Bull., 43, 932, 2008.
[10] Tripathy S. K., Sahoo T.,
Mohapatra M., Anand S., and Das
R. P., “XRD Studies on
Hydrothermally
Synthesized
BaTiO3 from TiO2-Ba(OH)2NH3 System” Mater. Lett., 59,
3543, 2005.
[11] Song Wei Lu, Burtrand I. Lee,
Zhong Lin Wang and William D.
Samuels,
“Hydrothermal
Synthesis
and
Structural
Charactrization
of
BaTiO3
Nanocrystals” J. Crystal Growth,
219, 269, 2000.
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
180
160
140
BT
120
100
BZ
80
60
BT
TiO2
BT
40
BZ
BT
BT
BT
BT
BZ
20
BZ
0
-20
0
10
20
30
40
50
60
70
80
90
2
Fig. 1 XRD pattern of as prepared BZT using TiO2, ZrOCl2 and Ba(OH)2 hydrothermally
treated at 150oC for 2h.
550
500
450
400
350
300
250
200
150
100
50
BZT2
BZT1
BT
0
-50
0
10
20
30
40
50
60
70
80
90
2 theta
Fig. 2 XRD pattern of as prepared BT, BZT1 and BZT2 using TiO2 and ZrO2 gels with
Ba(OH)2 hydrothermally treated at 150oC for 2h.
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
1600
1400
1
1200
2
1000
3
800
600
400
3
200
2
1
0
44.4
44.6
44.8
45.0
45.2
45.4
45.6
45.8
44.4
46.0
44.6
44.8
45.0
45.2
45.4
45.6
45.8
46.0
46.2
2 Theta
2 Theta
(a)
(b)
3
2
1
44.4
44.6
44.8
45.0
45.2
45.4
45.6
45.8
46.0
46.2
2 Theta
(c)
Fig. 3 XRD pattern at a limited range of 2 from 44.4 to 46o of a) BT, b) BZT1 and c)BZT2
at annealing temperature 1)500, 2) 700 and 3) 1000oC
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
4.030
4.025
lattice constant (a)
lattice constant (c)
4.020
lattice constant (a)
lattice constant (c)
4.028
4.026
4.024
4.022
4.015
lattice constant
Lattice constant 
4.020
4.010
4.005
4.000
3.995
4.018
4.016
4.014
4.012
4.010
4.008
4.006
4.004
3.990
4.002
4.000
3.985
3.998
0
200
400
600
800
0
1000
(a)
lattice constants A
200
400
600
800
Temperature C
Temperature C
(b)
4.034
4.032
4.030
4.028
4.026
4.024
4.022
4.020
4.018
4.016
4.014
4.012
4.010
4.008
4.006
4.004
4.002
4.000
3.998
3.996
lattice constant (a)
lattice constant (c)
0
200
400
600
800
1000
Temperature C
(c)
Fig. 4 Lattice constants with annealing temperature of a) BT, b) BZT1 and c) BZT2
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
1.010
BT
BZT1
BZT2
1.008
c/a
1.006
1.004
1.002
1.000
0
200
400
600
800
1000
Temperature C
Fig. 5 Tetragonality factor (c/a) as a function of annealing temperature of BT, BZT1
and BZT2.
1.008
1.007
c/a
1.006
1.005
1.004
1.003
0.000
0.002
0.004
0.006
0.008
Zr content
Fig. 6 Tetragonallity factor (c/a) as a function of Zr content at 1000oC.
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
(a)
(b)
Fig. 7 TEM images of as prepared BT powders
(a)
(b)
Fig. 8 SAED image of as prepared BT powders
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
(a)
(b)
Fig. 9 HRTEM image of as prepared BT powders.
(a)
(b)
Fig. 10 TEM images of as prepared BZT2 powders
(a)
(b)
Fig.11 SAED image of as prepared BZT2 powders
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Proceeding of the First Scientific Conference on Nanotechnology , Advanced Materials and Their Applications2009
(a)
(b)
Fig. 12 HRTEM image of as prepared BZT2 powders.
127