Effect of drying temperature on structure, phase transformation of sol-gel-derived lead zirconate titanate powders

Article abstract of DOI:10.1016/j.jallcom.2005.07.011

Lead zirconate titanate (PZT) (53/47) powders were prepared by a cheating acetate sol-gel process. The drying temperature effect on crystallization behavior was conducted to determine the best conditions for preparing high content of perovskite PZT powders in the morphotropic region. DSC/TG analysis, FT-IR spectrum and X-ray diffraction were carried out to identify the reaction sequences and calculated the activation energy of every transition temperature during the drying procedures. In the present work, well-crystallized, single-phase perovskite PZT powders were obtained after drying PZT stock solution at 300 °C for 1 h, then heat treatment at 600 °C for 30 min. The dependence of this crystallization temperature on the drying conditions was discussed.

Full text of DOI:10.1016/j.jallcom.2005.07.011

Journal of Alloys and Compounds 414 (2006) 224–229
Effect of drying temperature on structure, phase transformation
of sol–gel-derived lead zirconate titanate powders
a,∗
a,∗∗
b
c
Tien-I Chang , Jow-Lay Huang
, Hong-Ping Lin , Sheng-Chang Wang ,
d
e,f
a
Horng-Hwa Lu , Long Wu , Jen-Fu Lin
a
Department of Material Science and Engineering, National Cheng Kung University, No. 1 University Road, Tainan 701, Taiwan
b
Department of Chemistry, National Cheng Kung University, No. 1 University Road, Tainan 701, Taiwan
c
Department of Mechanical Engineering, Southern Taiwan University of Technology, No. 1, Nan-Tai St., Yung-Kang City, Tainan 710, Taiwan
d
Department of Mechanical Engineering, National Chin-Yi Institute of Technology, 35, Lane 215, Section 1, Chung-Shan Road,
Taiping City, Taichung County 411, Taiwan
Department of Electrical Engineering, National Cheng Kung University, No. 1 University Road, Tainan 701, Taiwan
e
f
F-Tech Corporation, No. 16 Nan-Ke 9th Road, Science-based Industrial Park, Tainan 741, Taiwan
Received 22 March 2005; accepted 3 June 2005
Available online 28 October 2005
Abstract
Lead zirconate titanate (PZT) (53/47) powders were prepared by a cheating acetate sol–gel process. The drying temperature effect on crys-
tallization behavior was conducted to determine the best conditions for preparing high content of perovskite PZT powders in the morphotropic
region. DSC/TG analysis, FT-IR spectrum and X-ray diffraction were carried out to identify the reaction sequences and calculated the activa-
tion energy of every transition temperature during the drying procedures. In the present work, well-crystallized, single-phase perovskite PZT
◦
◦
powders were obtained after drying PZT stock solution at 300 C for 1 h, then heat treatment at 600 C for 30 min. The dependence of this
crystallization temperature on the drying conditions was discussed.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Ferroelectrics; Sol–gel synthesis; X-ray diffraction; Thermal analysis
1
. Introduction
phase boundary (MPB) which separates the tetragonal (T)
and rhombohedral (R) phases from Ti- to Zr-rich regions,
respectively. At the MPB composition, PZT exhibits the best
piezoelectric properties.
Lead zirconate titanates (PZT, PbZrxTi1−xO3) are of great
interest due to their excellent piezoelectric properties [1].
PZT-based materials are widely used in transducers, fer-
roelectric memories, optical filters, shutters, actuators and
modulators. PZT exhibits non-centrosymmetric perovskite
structure below its Curie temperature (TC = 350 C). The
electromechanical response of these ceramics is maximum
High quality PZT powder is the important criterion to fab-
ricate the superior piezoelectric PZT ceramic materials. PZT
powders are usually prepared by solid-state reaction from
their constituent oxides [2,3]. However, the presence of inter-
mediate reactions between these oxides results in composi-
tional secondary phases and fluctuations [2,4,5]. In contrast
to the conventional solid-state reaction methods, wet chem-
ical route allows mixing of the component in the molecular
level, resulting in materials with high compositional homo-
geneity and low sintering temperatures. The alkoxide-based
sol–gel process is one of the most promising methods for
synthesizing ceramic powders.
◦
when x lies near the composition of the morphotrophic
∗
Corresponding author. Present address: No. 29, Dongfong Road, North
District, Tainan City 704, Taiwan, ROC. Fax: +886 6 2763586/2766464.
∗
∗
Corresponding author.
E-mail addresses: maxwell0926@yahoo.com.tw (T.-I. Chang),
JLH888@mail.ncku.edu.tw (J.-L. Huang).
0
925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.07.011

T.-I. Chang et al. / Journal of Alloys and Compounds 414 (2006) 224–229
225
◦
Titanium and zirconium are the electropositive features,
which present highly polar M O (M means titanium or zirco-
nium) bonds. It means that titanium and zirconium alkoxides
are extremely reactive towards water. In order to control
the undesired hydration from the moisture, it is important
to add some chelating agent into the PZT solution. Sev-
eral researches [6–9] reported that acetic acid can inhibit the
uncontrolled hydration of alkoxides on the preparation of
PZT powders by sol–gel. Among various acids, acetic acid
is commonly used. The role of the acetic acid represent as a
chemical modifier [6], chelating agent [7] or stabilizers [8,9].
Before the hydration and condensation process by adding
water into the sol–gel-derived solution, the addition of the
acetic acid acts as a chemical modifier by promoting a lig-
and exchange between the alcohol groups of the alkoxides
and the acetate groups of the acetic acid, resulting in a rel-
ative moisture insensitive precursor. The addition of acetic
acid indeed is a key factor to prepare the highly stable PZT
solution against moisture from the atmosphere [6–9].
the solution was heated to approximately 120 C and main-
tained for 2 h to remove the residual water and cooled in air
◦
to 80 C. A stoichiometric amount of zirconium n-propoxide
and acetic acid (CH3COOH, TDIA, 99.9%) was added to
◦
the lead acetate solution and refluxed at 120 C for 1 h to
form PZ solution. The ratio of lead acetate to acetic acid to
n-propyl alcohol is 10:5:1. After that, titanium iso-propoxide
was added to the PZ solution and further refluxed at 120 C
for 2 h to form the PZT (Zr/Ti = 53/47) solution.
PZT stock solution was used to produce dried gels which
were dried at 300 C for 1 h, defined as the H.T. dried gels and
at 150 C for 10 h, defined as the L.T. dried gels, respectively.
Finally, the dried gels were ground and calcined from 400 to
◦
◦
◦
◦
600 C for 30 min.
2.2. Characterization
The thermal properties of the gel powders were analyzed
using differential scanning calorimeter/thermo-gravimetric
analysis (DSC/TGA, Setaram Labsys-TGDSC DSC131,
Several researchers [10–13] had reported that by the
DTA/TGA analysis of PZT gels, there is an endothermic peak
◦
France), with various heating rates from 2.5 to 20 C/min.
◦
at 150 C which is attributed to the evaporation of solvents
The bonding conditions of the calcined PZT powders were
obtained by using a Fourier transform infrared spectrome-
ter (FT-IR, JASCO FT-IR-460 plus, Japan) with a frequency
ranging from 400 to 4000 cm . The crystal structures of
calcined PZT powders were identified by X-ray diffractome-
ter (XRD, Rigaku Geiger Flex, Japan) with Cu K␣ radiation
with low boiling point temperature and an exothermic peak
◦
exists at 300–360 C, which is attributed to the decompo-
−
1
sition of organic compounds [14]. Pyrolysis of dried PZT
gels is an important step on the way from metallo-organic,
amorphous precursors to inorganic ceramic materials. PZT
powders derived by sol–gel method are dried in two or more
stages in order to remove solvent completely [12]. But, fewer
studies focused on the effect of drying conditions of the PZT
powders. In order to identify the various drying conditions
thoroughly, we designed a new drying process depending on
the pyrolysis temperature of PZT gels in order to obtain a
homogeneous oxide mixture.
◦
˚
(λ = 1.5418 A) and a scanning step of 4 /min and 2θ angle
◦
◦
from 20 to 60 .
3. Results and discussion
Fig. 1 shows the results of DSC and TGA analysis of the
H.T. and L.T. dried gels. The terms 1–3 and A–E indicate
the endothermic and exothermic peaks in Fig. 1. The curve
in Fig. 1 can be divided into three regions. Region I, which is
The present study concerns the preparation of PZT
powders via the acetate sol–gel method. Acetic acid was
used as a chelating agent. Two drying temperatures (150
◦
◦
and 300 C) are applied in the study. The effect of drying
from room temperature to 200 C, refers to the evaporation
temperature on the crystallization behavior, the activation
energies of pyrolysis reactions and phase transformation are
discussed in the study.
of solvents as water or alcohol and region II ranges from
200 to 400 C which is responsible for the decomposition
◦
of organics as lead acetate. Region III, as the temperature
◦
above 400 C, defined as phase crystallization region of the
pyrochlore and perovskite phase. The DSC curves show two
endothermic peaks (i.e. peak 1 and peak 2) for both the H.T.
and L.T. dried gels below 100 C, which are corresponding to
2
. Experimental procedures
◦
2
.1. Powder preparation
the removal of solvent and/or moisture physically adsorbed
on the surface of the gels. Endothermic peak 3 appears at
Lead acetate trihydrate [Pb(CH3COO)2·3H2O, SHOWA,
9.5%], zirconium n-propoxide [Zr(OC3H7)4, STREM
◦
9
204 C, which is ascribed to melting of the anhydrous lead
chemicals, 75%] and titanium iso-propoxide [Ti(OCH
CH3)2)4, ACROS organics, 98%] were used as sources of
lead, zirconium and titanium to prepare PZT precursor solu-
tion. The whole process of the preparation of the precursor
solution is conducted in an ambient atmosphere.
acetate [Pb(CH3COO)2] [15]. The TGA curves (Fig. 1(b))
shows no weight loss at the endothermic temperature.
Furthermore, the DSC curves for various heating rates as
(
◦
shown in Fig. 2 indicate the reaction occurred at 204 C keep
in the same temperature when the heating rate increases. It
implies that the reaction at that temperature is a pure phys-
ical reaction. Peak A is responsible for the decomposition
reaction of the anhydrous lead acetate to the two kinds of
Firstly, lead acetate trihydrate was dissolved in n-propyl
alcohol (C3H7OH, ACROS organics, 99%) with the ratio of
◦
1
0 g:1 ml at 80 C in a three-neck reaction glass beaker. Then,

2
26
T.-I. Chang et al. / Journal of Alloys and Compounds 414 (2006) 224–229
Fig. 1. (a) DSC and (b) TGA curves of H.T. and L.T. dried gels.
Fig. 2. DSC curves of: (a) H.T. gels and (b) L.T. dried gels at different
heating rates.
intermediate basic acetate salts, Pb(CH3COO)2·PbO and
Pb(CH3COO)2·2PbO [15,16]. The endothermic reaction is in
good agreement with the previous studies [15,16]. According
to the reports [16,17], the major part of organic components
in the PZT dried gels are the acetate groups incorporated
from the lead acetate and the dynamic fragmentation pattern
for acid-catalyzed PZT gels was quite similar to that for pure
lead acetate trihydrate [17]. According to the high similarity
of the IR spectra [16] of lead acetate and PZT dried gels
in the carbonyl stretching region, the acetate groups are
bounded to Pb2 mostly in the dried gels. Nevertheless,
small amount of acetate groups could also be connected to
zirconium or titanium [16]. The DSC curve shows the L.T.
dried gel has a stronger endothermic reaction than H.T. gel
for peak A. Because the H.T. dried gels had been preheated
the more complex decomposition reactions and a stronger
endothermic reaction peak (Fig. 1(a)).
According to Merkle and Bertagnolli [16], the strong
exothermic peak B in Fig. 1 for both the H.T. and L.T. dried
gels is due to the decomposition of Pb(CH3COO)2·2PbO to
PbO1−x(CO3)x. It can be seen that the exothermic peak of
H.T. ones have a higher intensity. Because the weak-binding
acetic acid and/or acetate groups in the H.T. dried gels had
◦
been removed by preheating at 300 C for 1 h, the reaction
+
occurs at peak B for the H.T. series is only the formation
of PbO1−x(CO3)x. Otherwise, for the L.T. ones, the incom-
plete removal of the acetic acid and/or acetate groups will
lead to partial endothermic decomposition reaction for lead
subacetate, similar with the reactions of the peak A men-
tioned above. These reactions will reduce the intensity of the
exothermic peak B. Peak C is considered as the formation of
PbO phase and it will be confirmed by the XRD analysis as
shown in Fig. 4 [15]. For the L.T. dried gels, the peak C has a
smaller intensity than that of the H.T. ones. Peaks D and E are
assigned as the formation of the pyrochlore and perovskite
phase [17–23].
◦
at 300 C for 1 h, partial acetate groups were removed by the
heat treatment. The dominant endothermic reaction for the
H.T. dried gels is the decomposition of Pb(CH3COO)2·PbO
to Pb(CH3COO)2·2PbO. On the other hand, the L.T. dried
gels consist of Pb(CH3COO)2 to Pb(CH3COO)2·PbO and
Pb(CH3COO)2·PbO to Pb(CH3COO)2·2PbO. The lack of
◦
heat treatment at 300 C for the L.T. dried gels lead to

T.-I. Chang et al. / Journal of Alloys and Compounds 414 (2006) 224–229
227
Fig. 1(b) reveals the TGA result of the H.T. and L.T. dried
gels. In region I, the loss percentage of the H.T. and L.T.
dried gels are similar (about 5.804 and 5.091%). As dis-
cussed above, the decomposition reaction of the anhydrous
◦
lead acetate occurred in the region II between 200 and 400 C.
◦
In the early stage from 200 to 300 C for region II, the loss
percentage of the H.T. dried gels (14.909%) is obviously
less than the L.T. (20.339%). It is caused by the anhydrous
lead acetate partially decomposed by the preheating process
◦
at 300 C for 1 h for the H.T. ones. The intermediate basic
acetate salt decomposed and the PbO phase formed in the
post stage of region II and the loss percentage of the H.T.
dried gels (5%) is also less than the L.T. ones (6.251%). With
the exception that the total weight loss of the H.T. dried gels of
2
5% is less than the L.T. ones of 32%, indicating higher PZT
contents in the H.T. dried gels. It has been reported by Polli
24] that the powders with pre-pyrolysis would have higher
[
Fig. 3. FT-IR spectra of H.T. powders heated at various temperatures for
0 min.
PZT contents. With respect to color, the initial L.T. dried gels
are black, suggesting the presence of carbonaceous material.
The carbonaceous species could provide a local, low oxy-
gen partial pressure during pyrolysis [24], which will lead
to the Pb-partitioning. By contrast, the H.T. gels with fewer
carbonaceous materials can avoid the Pb-partioning and the
final PZT contents become higher.
3
Fig. 2 presents the various heating rates of the DSC curve
for the H.T. and L.T. dried gels. The dominant reactions
denoted A–E peaks are the same as Fig. 1. It is well known
that as the heating rate increases, the peaks shift to the higher
temperatures [25]. According to the Kissinger’s formula
[27,28], the activation energies can be estimated. The
activation energies (Ea) for various reactions were calculated
from the linear regression of the Kissinger’s formula, as
shown in equation (1), when the heating rates were 2.5, 5,
◦
1
0 and 20 C/min [27,28],
ꢀ
ꢁ
α
Tm
d ln
Ea
ꢀ
ꢁ = −
(1)
1
R
d
Tm
◦
where, α is the heating rate ( C/min), Tm the absolute temper-
ature (K) of the DSC curve and R represents the gas constant,
.314 J mol
−
1
−1
8
K . Following the Kissinger’s method, the
activation energies were calculated from the slope of the
plot of ln (α/Tm) and (1/Tm). Table 1 lists the activation
energies for the reactions A–E in Figs. 1 and 2. Peak D is
responsible for the formation of the cubic pyrochlore phase.
The data shows that the activation energy of the pyrochlore
phase formation is similar for the H.T. and L.T. dried gels.
Peak E is assigned as the formation of the dominant PZT
perovskite phase. The activation energy for the H.T. dried
gels is significantly lower than L.T. dried gels. It means that
the H.T. dried gels transform to the perovskie PZT phase
easily and will have higher proportion of the PZT phase.
From the DSC curves in Fig. 1, both the H.T. and L.T.
dried gels decomposed from the anhydrous lead acetate to
the PbO phase. However, Table 1 does not list the activa-
Fig. 4. XRD patterns of: (a) H.T. and (b) L.T. powders calcined at various
temperatures for 30 min.

2
28
T.-I. Chang et al. / Journal of Alloys and Compounds 414 (2006) 224–229
Table 1
Activation energies of various reactions for H.T. and L.T. dried gels
Reactions Reactions
Ea of H.T. dried gel
Ea of L.T. dried gel
−
1
−1
(
kJ mol
)
(kJ mol
)
(
(
(
(
(
A) The decomposition of acetate groups Pb(CH3COO)2 → Pb(CH3COO)2·PbO → Pb(CH3COO)2·2PbO
24.9 ± 1.9
56.2 ± 2.7
29.8 ± 1.7
32.9 ± 1.9
B) The decomposition of acetate groups
C) The formation of lead oxide
D) The formation of pyrochlore phase
E) The formation of perovskite phase
a
Pb(CH3COO)2·2PbO → PbO1−x(CO3)x
a
PbO1−x(CO3)x → PbO
210.0 ± 7.4
351.4 ± 19.5
424.5 ± 23.6
–
–
345.3 ± 24.2
591.3 ± 41.3
Accompany reaction of 2PbO + C → 2Pb + CO2 occurs at this reaction stage.
◦
tion energy of peak C of the L.T. gels. The L.T. dried gels
with higher residual carbon content will lead to the reduc-
tion of the PbO to element Pb and accompany reaction of
to 550 C, the XRD peaks identified as the PZT phase and the
pyrochlore phase appear at the same time. The XRD peaks
confirm the reactions for the peaks D and E in the DSC result
◦
2
PbO + C → 2Pb + CO2 occurs at this reaction stage.
and the M–O bonding at 550 C in the FT-IR spectrum. When
the temperature increases to 600 C, the proportion of the
◦
The FT-IR spectrum of the H.T. dried gels heated at differ-
ent temperature for 30 min is shown in Fig. 3. The absorption
pyrochlore phase apparently decreases and the crystallinity
of the perovskite phase crystallized more completely.
Fig. 4(b) demonstrates the XRD results of the L.T. dried
−
1
band at 3400 cm corresponds to the stretching of −OH
−
1
group [26]. Peaks around 1640 and 1315 cm are corre-
sponding to free acetic acid or unidentate acetate [14]. There
◦
gels heated at the same conditions. At 400 C for 30 min,
−
1
are two absorption bands at 1420 and 1560 cm which are
the Pb-partioning occurs in the L.T. dried gels in contrast
to the PbO phase in the H.T. ones at the same tempera-
ture. The reason for the Pb-partitioning is attributed to the
carbonate—the reducing agent—in the dried gels, which
will lead to the reduction of the PbO phase to element
Pb. The Pb-partitioning destroys the homogeneous distri-
bution of all compositions in the amorphous PZT pow-
ders. The insignificant peak C in DSC shown in Fig. 1
is caused both by the endothermic decomposition reaction
(Pb(CH3COO)2·2PbO to PbO) and the exothermic replace-
ment reaction (2PbO + C → 2Pb + CO2). For the L.T. dried
gels, the vague peak C and the higher total weight loss ratio
in the DSC/TGA analysis all serve as another evidence of the
−
attributed to the symmetric and asymmetric –COO stretch-
ing modes of the acetate groups [18]. The separation wave
number between those two stretching modes (ꢀν) is a char-
acteristic value, depending on the way carboxylate binds to
−
1
the metal. If the ꢀν value is less than 80 cm , acetate is
typically a cheating bidentate ligand. Otherwise, as the ꢀν
−
1
value is higher than 160 cm , acetate is typically a bridging
−
1
bidentate ligand [6]. The peaks around 1000 cm indicate
that carbonate presents in the dried gels. It is interesting to
note that due to the PZT, solution was heated at the tempera-
ture higher than the lead acetate decomposition temperature,
the peaks defined as the basic intermediate acetate salt occur
at 1050, 1020, 940, 930, 860, 666 and 620 cm . Moreover,
most of lead acetate has been decomposed completely in
the H.T. dried gels heated at 500 C for 30 min. The same
−
1
◦
Pb-partitioning. As the temperature rises to 500 C, the peaks
of the PbO and pyrochlore appear and the intensity of element
Pb decreases. It is suggested that the formation of the PbO
phase came from the oxidation of Pb or the product of the
final decomposition reaction of the anhydrous lead acetate.
◦
results can be proven by the disappearance of 1420 and
−
1
1
560 cm peaks. On the other hand, the PbO peak appears
−
1
◦
at the frequency region of 300–500 cm , which is in good
agreement with the XRD result shown in Fig. 4. A sharp spec-
trum of 600 cm peak shows in the H.T. dried gels heated at
As temperature increases to 550 C, it shows the same ten-
dency as the H.T. dried gels. The perovskite phase presents at
−
1
◦
◦
550 C and crystallizes more completely at 600 C. However,
the contents of the pyrochlore phase are higher than the H.T.
◦
5
50 C, that refers to the M–O bonding (M means the metal
◦
element) [26]. Therefore, the formation temperature of the
dried gels at 600 C. It is worth to be noted that whether the
◦
perovskite PZT should be above than 550 C, which is in
Pb or PbO phase appear or not, the perovskite phase will be
alwaysformedandtheresultisinagreementwiththeprevious
study [24]. However, in this study, the formation temperature
agreement with the DSC result in Fig. 1. The tendency of the
L.T. dried gels for the FT-IR spectrum is the same as the H.T.
ones (not shown here).
◦
(550 C) for the perovskite phase is lower than the previous
◦
Fig. 4(a) shows the XRD results of the H.T. dried gels
study (700 C) [24]. It could be due to the effective removal
◦
heated at various temperatures for 30 min. At 400 and 500 C
of the organic residues in the PZT gels before calcinations.
The relative perovskite content at various temperatures
can be estimated from the intensities of the perovskite
(1 1 0) peak and pyrochlore (2 2 2) peak using the relation
Ipero(1 1 0)/(Ipero(1 1 0) + Ipyro(2 2 2)) [6,9]. Fig. 5 displays
evolution of the relative perovskite phase content of the
H.T. and L.T. dried gels calcined at various temperatures for
for 30 min, the dominant phase is the PbO. With increasing
◦
the temperature from 400 to 500 C, the intensity of the PbO
phase increases. The results indicate that the crystallinity of
the PbO phase is enhanced with the increasing of tempera-
ture. The XRD result is in agreement with the decomposition
reaction of the anhydrous lead acetate to the PbO phase at
◦
◦
4
5
00 C in the DSC result and also with the Pb–O bonding at
30 min. As the temperature is below 500 C, the perovskite
◦
00 C in the FT-IR spectrum. As the temperature increases
content is too low to detect. When the temperature is above

T.-I. Chang et al. / Journal of Alloys and Compounds 414 (2006) 224–229
229
phase. From the FT-IR and XRD analyses, the L.T. dried gels
contain more carbonaceous materials, which lead to the Pb-
partitioning and the relative PZT perovskite contents become
lower. Ontheotherhand, byusingtheH.T. driedgels, itissuc-
cessfully achieved to decrease the calcination temperature to
◦
6
00 C and to obtain fine-grained, high content of perovskite
PZT phase.
Acknowledgment
The authors would like to thank the National Science
Council of Taiwan, Republic of China, for its financial sup-
port under Contract No. NSC 91-2216-E006-042.
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Fig. 5. Evolution of perovskite phase content of H.T. and L.T. powders
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◦
◦
[
[
[
4
. Conclusions
[
[
[
This study investigated the effects of different drying
conditions for the PZT dried gels transformed to per-
ovskite phase. From the thermal analyses, the PZT dried
gels will transform to terminal perovskite phase and sev-
eral intermediate products, including Pb(CH3COO)2·PbO,
Pb(CH3COO)2·2PbO, PbO1−x(CO3)x, PbO and pyrochlore
were present in sequence. The weight loss of the H.T. dried
gels in region II, in which organic residues decomposed, is
lower than the L.T. ones. It reflects that the anhydrous lead
2
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[
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[
(
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acetate partially decomposed by the preheating process at
◦
3
00 C for 1 h for the H.T. dried gels. Moreover, the total
weight loss of the H.T. dried gels is less than the L.T. ones,
which indicate higher PZT contents in the H.T. dried gels.
The activation energies for the various reactions were calcu-
lated from the linear regression of the Kissinger’s formula
and the activation energy of the perovskite formation for the
H.T. dried gels is significantly lower than L.T. dried gels. It
means that the H.T. dried gels transform to the perovskite
PZT phase easily and will have higher proportion of the PZT
[
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(
[
[
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1
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