Abstract Zinc titanate (ZnTiO 3 ) powders of perovskite structure were synthesized by conventional solid state reaction using metal oxides. Powders of ZnO and TiO 2 in a molar ratio of 1:1 were mixed in a ball mill and then heated at temperatures from 700 to 1000 • C for various time periods in air. The crystallization temperature of ZnTiO 3 powder was ∼820 • C, activation energy for crystallization was ∼327.14 kJ/mol and for grain growth was ∼48.84 kJ/mol. A transition point was observed when the electrical resistivity was measured versus temperature. Like some ferroelectric materials, a PTCR behavior above the transition temperature was observed with Curie temperature of ∼5 • C

Guo-Ju Chen

In-Gann Chen

Sean Wu

Te-Hua Fang

Yee-Shin Chang

Yen-Hwei Chang

Yin-Lai Chai

CiteSeerX

Ceramics International 30 (2004) 2183–2189
Synthesis, formation and characterization of ZnTiO3 ceramics
Yee-Shin Changa, Yen-Hwei Changa,∗, In-Gann Chena, Guo-Ju Chenb,
Yin-Lai Chaic, Te-Hua Fangd, Sean Wue
a Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
b Department of Material Science and Engineering, I-Shou University, Kaohsiung 840, Taiwan, ROC
c Department of Resources Engineering, Dahan Institute of Technology, Hualien 971, Taiwan, ROC
d Department of Mechanical Engineering, Southern Taiwan University of Technology, Tainan 710, Taiwan, ROC
e Department of Electronics and Information Engineering, Tung-Fang Institute of Technology, Kaohsiung 821, Taiwan, ROC
Received 5 September 2003; received in revised form 2 January 2004; accepted 29 January 2004
Available online 14 April 2004
Abstract
Zinc titanate (ZnTiO3) powders of perovskite structure were synthesized by conventional solid state reaction using metal oxides. Powders
of ZnO and TiO2 in a molar ratio of 1:1 were mixed in a ball mill and then heated at temperatures from 700 to 1000◦C for various time
periods in air. The crystallization temperature of ZnTiO3 powder was∼820◦C, activation energy for crystallization was∼327.14 kJ/mol and
for grain growth was∼48.84 kJ/mol. A transition point was observed when the electrical resistivity was measured versus temperature. Like
some ferroelectric materials, a PTCR behavior above the transition temperature was observed with Curie temperature of∼5 ◦C.
© 2004 Elsevier Ltd and Techna S.r.l. All rights reserved.
Keywords: A. Powders: solid state reaction; C. Dielectric properties; C. Electrical properties; D. Perovskites
1. Introduction
Fundamental studies concerning the phase diagram and
the characterization of the ZnO–TiO2 system have been pub-
lished by Dulin and Rase[1] and Bartram and Slepetys[2]
since 1960s. They reported that there are three compounds
existing in the ZnO–TiO2 system including-Zn2TiO4 (cu-
bic), Zinc titanate (ZnTiO3, hexagonal), and Zn2Ti3O8 (cu-
bic). ZnTiO3 was of a perovskite type oxide structure and
could be a useful candidate as microwave resonator[3],
gas sensor[4] (for ethanol, NO, CO, etc.), and paint pig-
ment. In addition, ZnTiO3 doped with some transition metal
ions could be applied in luminescent purposed by Wang
et al.[5,6]. Yamaguchi et al.[7] clarified that Zn2Ti3O8 is a
low-temperature form of ZnTiO3. Zn2TiO4 can be easily pre-
pared by the conventional solid state reaction between 2ZnO
and 1TiO2. Nevertheless, the preparation of pure ZnTiO3
from a mixture of 1ZnO and 1TiO2 has not been successful
because the compound decomposes into-Zn2TiO4 and ru-
tiles at about 945◦C. There are several methods to prepare
∗ Corresponding author. Tel.:+886-6-2757575x62941;
fax: +886-6-2382800.
E-mail address: enphei@mail.ncku.edu.tw (Y.-H. Chang).
ZnTiO3 powder including solid state reaction[1], sol–gel
[7,8], etc. Zinc titanate nano-crystalline powders prepared
by the sol–gel technique have been reported by our earlier
study [8] but the processes are generally complicated and
the reagents used are very expensive. In this study, the au-
thors have attempted to synthesize ZnTiO3 powders by con-
ventional solid state reaction which is simpler to operate
and which uses cheap and easily available oxides as starting
materials. The kinetic behavior of the reaction and the char-
acteristics of the resulting ZnTiO3 powders were examined.
2. Experimental
2.1. Powders preparation
The ZnTiO3 powders were prepared by conventional solid
state reaction using 99.99% pure ZnO and TiO2 powders
as the starting materials (Aldrich, USA). Even though the
starting materials are not very sensitive to moisture, the han-
dling of chemicals was carried out in dry N2 atmosphere.
The starting materials were mixed in ethanol by ball milling
for 24 h with zirconia balls in polyethylene jars and dried
at 120◦C. Four calcination temperatures were selected to
0272-8842/$30.00 © 2004 Elsevier Ltd and Techna S.r.l. All rights reserved.
doi:10.1016/j.ceramint.2004.01.002
2184 Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189
investigate the reaction of formation of zinc titanate: 700,
800, 900, and 1000◦C, respectively, all for 24 h. After hav-
ing established the optimum calcination temperature, alter-
native times of 12, 24, 48, and 72 h were applied at that
temperature. Before measuring their properties, the powders
were pressed at∼50 kg/cm2 into discs of 10 mm in diame-
ter, 5 mm thickness, and 1.6 g weight. Then, the discs were
sintered at temperatures of 800–940◦C for 24 h.
2.2. Characterizations
Powders were analyzed for crystalline structure by X-ray
diffractometry (XRD, Rigaku) using Cu K radiation to
identify the possible phases formed after heat treatment. The
average grain sizes of powders were calculated according to
the Scherrer’s equation. The surface morphology was exam-
ined by scanning electron microscopy (HR-SEM, S4200, Hi-
tachi). Differential scanning calorimetry measurements were
carried out in an HT-DSC (DSC, Model 404, Netzsch Inc.,
Exton, PA) equipment in order to investigate the ZnTiO3
phase formation and calculate the activation energies of
powders transforming from amorphous to the crystalline
state using Kissinger’s equation. Samples of about 2–3 mg
were placed inside the closed platinum cups. The measure-
ments were carried out with temperature rise at 10, 20, 30,
and 40◦C/min, respectively, in a dry nitrogen (99.99%) at-
mosphere. The calibration was performed using gold as the
standard. Temperature dependence of dielectric constant
was measured with an inductance–capacitance–resistance
(LCR) (Hewlett-Packard, HP-4284A) meter at 1 kHz dur-
ing the heating and cooling of the sample at 4◦C/min. The
electric resistivity was measured between 0 and 40◦C using
a multimeter (Hewlett-Packard, HP-3457A).
3. Results and discussion
3.1. Crystallization behavior of ZnTiO3 powders
Fig. 1shows the XRD patterns of the ZnO and TiO2 pow-
der mixtures calcined at various temperatures. At 700◦C,
there are some peaks of ZnTiO3 shown in the pattern but
the peak intensity is low and some intermediate phases are
formed. In the pattern of the mixture calcined at 800◦C for
24 h, no peaks of the starting samples can be observed and
all peaks were assigned to the hexagonal ZnTiO3 phase with
lattice constants:a = 5.077 Å, andc = 13.92 Å (JCPDS
No. 14-0033).Fig. 2 shows the XRD profiles of ZnTiO3
powders after heat treatment at 800◦C for (a) 12 h, (b) 24 h,
and (c) 48 h. Single phase ZnTiO3 was observed for var-
ious calcination times, however, the intensity of ZnTiO3
peaks increased with increasing time. When calcined for
48 h, traces of-Zn2TiO4 and rutile phases appeared. This
may be caused by the reduction of zinc oxide to volatile
elemental zinc resulting in a deficiency of zinc in ZnTiO3
which thus becomes sub-stoichiometric and decomposed.
Fig. 1. XRD profiles of ZnTiO3 powder calcined at (a) 700◦C, (b) 800◦C,
(c) 900◦C, and (d) 1000◦C for 24 h in air.
Fig. 2. XRD profiles of ZnTiO3 powder calcined at 800◦C for (a) 12 h,
(b) 24 h, and (c) 48 h.
Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189 2185
3.2. Average grain sizes and activation energy of grain
growth of ZnTiO3 powders
The average grain sizes were determined from XRD pow-
der pattern according to the Scherrer’s equation[9]
D = kλ
β cosθ
(1)
whereD is the average grain size,k is a constant equal to
0.9, λ is the X-ray wavelength equal to 0.1542 nm, andβ
is half the peak width. The average grain sizes of powders
calcined at 700, 800, and 900◦C were about 540, 700, and
900 nm, respectively. According to Coble’s theory[10], the
activation energy of grain growth during powder sintering
can be calculated by an Arrhenius equation
dlnK
dT
= Q
RT2
(2)
whereK is the specific reaction rate constant,Q is the ac-
tivation energy,T is the absolute temperature, andR is the
ideal gas constant.
Bolen and co-workers showed that the value ofK is re-
lated with grain size directly[11]. Thus integral ofEq. (2)
becomes
logD =
( −Q
2.303R
)
1
T + A (3)
whereD is the grain size andA is the intercept.
Fig. 3. Plot of log(grain size) vs. 1/T × 1000.
From Eq. (3), by making a plot of logD versus the re-
ciprocal of absolute temperature (1/T), a straight-line was
obtained as shown inFig. 3. The slope of the resulting Ar-
rhenius plot is−Q/(2.303R) and the activation energy of
grain growth can be obtained and the value ofQ is about
48.84 kJ/mol.
3.3. DSC analysis of ZnTiO3 powders
Fig. 4 gives the curves of DSC analysis of ZnTiO3
powders heated at different heating rates of (a) 10◦C/min,
(b) 20◦C/min, (c) 30◦C/min, and (d) 40◦C/min, respec-
tively. At a heating rate of 10◦C/min, there appears an
endothermic peak near 820◦C showing the formation of
ZnTiO3 crystalline phase. This endothermic peak shifts
to higher temperatures with increasing heating rate. The
temperature was higher than that for the powder prepared
by the sol–gel technique[8], this possibly being related
to the larger grain size produced by the solid state re-
action than for the sol–gel technique. The crystallization
activation energy of ZnTiO3 powders was calculated from
the relationships of different heating rate versus the en-
dothermic peak value by using the Kissinger’s equation
[12]
ln
(
β
Tp2
)
= − Q
RTp
+ C (4)
2186 Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189
Fig. 4. DSC curves of ZnTiO3 powders obtained at different heating rates of (a) 10◦C/min, (b) 20◦C/min, (c) 30◦C/min, and (d) 40◦C/min.
Fig. 5. Plot of ln(β/Tp2) vs. 1/Tp.
Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189 2187
whereβ is the heating rate,Tp is the temperature of the
endothermic peak,R is the ideal gas constant which equals
to 8.314 J/mol,Q is the activation energy, andC is a con-
stant. Making a plot of ln(β/Tp2) versus the reciprocal
of absolute temperature (1/Tp) as shown inFig. 5, the
activation energy of crystallization of ZnTiO3 is shown
to be 327.14 kJ/mol which is larger than the one result-
ing for ZnTiO3 crystallization from the sol–gel technique
[8].
Fig. 6. SEM micrographs of ZnTiO3 powders calcined at (a) 700◦C, (b)
800◦C, and (c) 900◦C for 24 h in air.
3.4. SEM micrographs of ZnTiO3 powders
Fig. 6 shows the SEM micrographs of ZnTiO3 powders
calcined at different temperatures: (a) 700◦C, (b) 800◦C,
and (c) 900◦C for 24 h in air. The sphere like particles
seemed to distribute homogeneously, and the particle size
increases with the increase in the calcination temperature
(the particle size is about 0.5–1m for calcination tem-
peratures from 700 to 900◦C). It is believed that a higher
temperature enhanced higher atomic mobility and caused
Fig. 7. SEM micrographs of ZnTiO3 powders calcined at 800◦C for (a)
24 h, (b) 48 h, and (c) 72 h in air.
2188 Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189
Fig. 8. Temperature dependence of electrical resistivity for ZnTiO3 sintered
at 900◦C.
faster grain growth, thus resulting in better crystallinity
as confirmed by the X-ray diffraction analysis.Fig. 7
shows the SEM micrographs of ZnTiO3 powders calcined
at 800◦C for (a) 12 h, (b) 24 h, and (c) 48 h in air. The
size of particles appears to increase with the increase in
Fig. 9. Temperature dependence of dielectric constant and dielectric loss at 1 kHz for ZnTiO3 sintered at 900◦C.
calcination time. As discussed earlier, the longer calci-
nation time tends to promote phase formation and grain
growth.
3.5. Electrical resistivities
ABO3 perovskite type structure possesses semicon-
ducting behavior. Some semiconducting materials exhibit
anomalously strong (exponential) increase in the resistivity
ρ with temperatureT near the ferroelectric Curie tempera-
ture, Tc. This anomalous behavior (ofρ) is well-known as
the positive temperature coefficient of resistivity (PTCR)
[13] and has been associated to an electrical potential
barrier from the presence of a two-dimensional surface
layer of acceptor state, e.g., segregation acceptor ions, or
adsorbed oxygen at the grain boundaries of the ceramic
materials[14]. The results of earlier studies showed that
some materials with ABO3 structure present a V-type
resistivity–temperature characteristics[15–17] which was
believed to be intrinsic to semiconducting ceramics with
ABO3 structure.Fig. 8shows the electrical resistivities as a
function of temperature between 0 and 40◦C. It, however,
shows a semiconductor behavior in the low-temperature
region and a metal-like behavior above the transition tem-
perature.Fig. 9 shows the temperature dependence of di-
electric constant for ZnTiO3 sintered at 900◦C measured
at 1 kHz. The Curie temperature may be located at around
5◦C.
Y.-S. Chang et al. / Ceramics International 30 (2004) 2183–2189 2189
4. Conclusions
ZnTiO3 powders have been synthesized successfully by
solid state reaction. The best conditions for the formation
of ZnTiO3 have been found to be 800◦C and 24 h ther-
mal treatment. The grain size of ZnTiO3 powders calcined
at various temperatures was about 0.5–1.0m. DSC anal-
ysis revealed the temperature of ZnTiO3 phase formation
to be about 820◦C, the activation energies for the forma-
tion of ZnTiO3 phase was about 327.14 kJ/mol and for grain
growth was 48.84 kJ/mol. All these figures were higher than
for ZnTiO3 synthesized by the sol–gel technique. Like some
ferroelectric materials, a PTCR behavior above the transi-
tion temperature was observed for ZnTiO3 with Curie tem-
perature at about 5◦C.
Acknowledgements
Authors wish to thank the Nation Science Council of Tai-
wan for supporting the project (NSC92-2216-E-006-038).
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Synthesis, formation and characterization of ZnTiO3 ceramics,Ceram

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Synthesis, formation and characterization of ZnTiO3 ceramics,Ceram

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