Ferroelectric lead zirconate titanate films prepared by spray pyrolysis of carboxylate solutions

Article abstract of DOI:10.1023/A:1017537102999

Ferroelectric PbTi_0.6Zr_0.4O₃films 0.5-1.5 μm in thickness were produced on platinum substrates by spray pyrolysis of carboxylate solutions. The optimized compositions of the precursor solutions, containing methacrylic acid

Full text of DOI:10.1023/A:1017537102999

Inorganic Materials, Vol. 37, No. 5, 2001, pp. 500–507. Translated from Neorganicheskie Materialy, Vol. 37, No. 5, 2001, pp. 596–604.
Original Russian Text Copyright © 2001 by Tomashpol’skii, Rybakova, Lunina, Fedoseeva, Prutchenko, Men’shikh.
Ferroelectric Lead Zirconate Titanate Films Prepared
by Spray Pyrolysis of Carboxylate Solutions
Yu. Ya. Tomashpol’skii, L. F. Rybakova, T. V. Lunina, O. F. Fedoseeva,
S. G. Prutchenko, and S. A. Men’shikh
Karpov Research Institute of Physical Chemistry (Russian State Scientific Center),
ul. Vorontsovo pole 10, Moscow, 103064 Russia
Received February 17, 2000
Abstract—Ferroelectric PbTi Zr O films 0.5–1.5 µm in thickness were produced on platinum substrates
0
.6 0.4
3
by spray pyrolysis of carboxylate solutions. The optimized compositions of the precursor solutions, containing
methacrylic acid and ethylene glycol, are stable under normal conditions, allow the annealing temperature to
be reduced, and lead to higher quality film surfaces and large grains. The film exhibit the following electrical
properties: T = 360–460°C, ε
= 1750 at T , tanδ = 0.02–0.1 at 1 kHz and room temperature, P
=
C
max
C
smax
2
2
1
8 µC/cm , P
= 15 µC/cm at 50 Hz, and E = 42–120 kV/cm.
rmax
c
INTRODUCTION
to prepare a true solution, used Ti, Zr, and Pb chlorides
dissolved in urea; the pH of the solution was adjusted
to 5.5 by controlled aluminum hydroxide additions.
PZT films 1.1–1.2 µm in thickness were prepared by
dipping substrates into the solution thus prepared, fol-
lowed by slow pulling. De Veirman et al. [9] prepared
Lead zirconate titanate (PZT) ceramics are widely
used in microelectronics, acousto- and optoelectronics,
computer engineering, and sensors owing to their supe-
rior ferro-, piezo-, and pyroelectric properties [1]. PZT
films have even greater potential for practical applica-
tion, since they offer better sensor properties, faster
PbTi0.45Zr0.55O films up to 0.08 µm in thickness using,
3
response, and higher selectivity; their production as a precursor solution, a mixture of Pb(C
requires less power; and they can readily be integrated Ti(OBu-n) , and Zr(OPr-n) dissolved in isopropanol
H15COO) ,
7 2
4
4
into semiconductor technology [2]. Intensive research
effort is being concentrated on the preparation of PZT
films by chemical means, in particular, via precipitation
from solution.
(
30–50%). The solution was applied to the substrate by
spin coating. PZT films with Ti : Zr = 52 : 48 were
obtained from solutions of Ti[(CH ) CHO] ,
Zr(C H O) , and Pb(CH CO ) in glacial acetic acid,
3
2
4
3
7
4
3
2 2
Mansour et al. [3, 4] prepared PZT films 0.8–1.0 µm
in thickness by applying zirconium and titanium alkox-
ide solutions to a substrate; Pb was introduced as an
acetate. Afanas’ev et al. [5] used a solution of
distilled water, and propanol [10]. The solutions were
applied to the substrate by spin coating. The film thick-
ness was Ӎ1 µm. Lemanov et al. [11] prepared PZT
films from 0.2 M solutions of the methyl cellosolvates
Zr(C H COO) ,
Pb(2-C H -C H COO) ,
and
7
15
4
2
5
5
10
2
Pb(OC H OCH ) ,
Ti(OC H OCH ) ,
and
2
2
3 2
2
2
3 4
[
(CH ) Ti(neo-C H COO) ] in xylene. Layers were
3
2
9
19
2
Zr(OC H OCH ) with components in the ratio Pb : Ti :
2
2
3 4
deposited onto a rotating substrate. PZT films with
Ti : Zr = 0.25–0.75 were also prepared by precipitation
from solutions of lead 2-ethyl hexanoate, tetrabutyl
titanate, and zirconium acetylacetonate in butanol [6].
To prevent the formation of the nonferroelectric, pyro-
chlore phase and compensate for the vaporization of
lead oxide, an excess of Pb (2–12 mol %) was intro-
duced into the precursor solution. La-doped PZT films
were prepared by precipitation from a water–methanol
Zr = 1.05 : 0.52 : 0.48. The solution were prepared by
anodic dissolution of Pb, Ti, and Zr in methyl cello-
solve, followed by spin coating. Thus, despite the wide
diversity of the precursors used, the carboxylate route
has received insufficient attention. At the same time,
carboxylate solutions are easy to prepare, stable in air
under ordinary conditions, and relatively inexpensive.
They require no complex equipment to prevent contact
with moisture or oxygen. Earlier, the carboxylate route
was used with success to prepare superconducting
cuprate films [12, 13]. Besides, of the many techniques
(
4 : 1 by weight) solution of zirconium and lanthanum
acetates, titanium acetylacetonate, and lead basic ace-
tate [3, 4, 7]. The substrates were slowly pulled from
the solution. The solution pH was adjusted by aqueous for applying solutions to substrates, spray pyrolysis,
ammonia or acetic acid. Acidic solutions were found to undeservingly seldom used at the moment, is the easi-
be more stable; the use of alkaline solutions led to gela- est to implement, offers high flexibility of the process,
tion of the precipitate. Ozenbaz and Ergin [8], in order and appears to be commercially viable. The objective
0
020-1685/01/3705-0500$25.00 © 2001 MAIK “Nauka/Interperiodica”

FERROELECTRIC LEAD ZIRCONATE TITANATE FILMS
501
of this work was to develop and optimize a procedure and stable under normal conditions and wetted the sub-
for producing PZT films from carboxylate solutions.
strates (polished Pt plates 12 × 4 mm in size, rinsed in
extrapure-grade hexane and distilled water).
Spray coating. The precursor solutions were
diluted with the solvents indicated above to a concen-
tration of 2–4 g/l. Next, one of the solutions was intro-
duced into an atomizer, propelled by compressed air
EXPERIMENTAL
Preparation of the precursor solutions. We pre-
pared solid solutions with Ti : Zr = 0.6 : 0.4. The starting
reagents were lead acetate trihydrate, Pb(CH COO) ·
(0.5 MPa), and directed through a nozzle onto a pre-
3
2
heated substrate, situated 3–5 mm away from the outlet.
The flow rate of air was 5–6 l/min, and the ejection
velocity was 80–100 m/s. The consumption of the solu-
tion was 10–15 ml/h. Large drops (50–100 µm) were
trapped and brought back to the atomizer. Also, large
drops were prevented from reaching the substrate by
the bent outlet tube, where the aerosol flow changed
direction by 45°, so that the largest drops deposited on
the wall. On the preheated substrate, part of the solvent
vaporized, and the viscosity of the solution increased
considerably. Each layer was deposited for 30 min;
then, the deposit was dried at 350°C for 20 min, and the
next layer was deposited. After the desired thickness
was attained, the film was dried at 350°C for 4–8 h. As
a result, the metalorganic precursors fully decomposed,
3
H O; titanium isopropoxide, Ti(OC H ) ; and zirco-
2 3 7 4
nium acetylacetonate decahydrate, Zr(C H O ) · 10H O.
5
7
2 4
2
Isopropanol and hexane were dehydrated by standard
techniques [14] and then distilled over Na in an argon
atmosphere. Titanium tetrachloride was distilled at
atmospheric pressure in argon. Acetic acid was dehy-
drated and purified by freezing, followed by atmo-
spheric-pressure distillation. Methacrylic acid was
purified by reduced-pressure distillation over a poly-
merization stabilizer (copper powder). ZrOCl · 8H O
was purified by recrystallization, since it readily dis-
solves in water but is poorly soluble in cold 25 to 30%
hydrochloric acid. In this way, we were able to remove
Al, Fe, Nb, Ta, and Ti impurities.
2
2
Titanium isopropoxide was synthesized by a stan- and a dense layer consisting of fine-particle Pb, Ti, and
dard technique in a dry argon flow. Isopropanol was Zr oxides was formed. This layer was then heat-treated
placed in a flat-bottom, three-mouth flask fitted with a at a high temperature. In this way, we prepared 18 films
stirrer, thermometer, dropping funnel, and refluxer with (Table 1).
a T-joint for introducing and removing argon. Next, an
Annealing conditions. The films were annealed in
appropriate amount of Na metal was added with heat-
a Nabertherm L3/S furnace under a controlled temper-
ing, until complete dissolution, and titanium tetrachlo-
ride was introduced through a dropping funnel. As a
result, we obtained a sodium chloride precipitate in an
alcoholic medium.
ature program (±1°C). A typical annealing schedule
included heating to t for time τ , holding at t for time
1
1
1
τ , heating to t for time τ , holding at t for time τ ,
2
2
3
2
4
heating to t for time τ , holding at t for time τ , and
3
5
3
6
The titanium alkoxide was separated from the reac-
tion mixture by threefold extraction by hexane, fol-
lowed by centrifugation. The liquid phases were poured
together and distilled. Next, hexane and isopropanol
were distilled off consecutively. Titanium isopropoxide
was isolated by vacuum distillation with a yield of
furnace-cooling. The annealing parameters were as
follows:
t1 = 350°C
t2 = 650°C
τ1 = 1 h
τ3 = 2 h
τ2 = 1 h
τ4 = 4 h
Nos. 1–6
5
9.7%.
t1 = 350°C
t2 = 750°C
τ1 = 1 h
τ2 = 3 h
τ4 = 1 h
Nos. 7–12
To obtain zirconium acetylacetonate, zirconium
τ3 = 5.3 h
oxychloride recrystallized from a chloride solution was
dissolved in distilled water. After cooling, the solution
was mixed with a 10% solution of acetylacetone in
sodium carbonate, which was preliminary cooled and
t1 = 350°C
τ1 = 5 h
τ2 = 4 h
Nos. 13–18
t2 = 750°C
τ3 = 5 h
τ4 = 1 h
filtered. The resulting crystalline Zr(C H O ) · 10H O
3
7
2 4
2
t3 = 850°C
τ5 = 4.5 h
τ6 = 1 h
precipitate was collected on a filter and washed with
distilled ice water. After dissolving zirconium acetylac-
etone in benzene and separating insoluble zirconium The cooling rate was 3°C/min (Table 1).
The heating rate was varied from 0.98 to 2.5°C/min.
oxychloride by filtering, zirconium acetylacetonate
was precipitated by petroleum ether with a yield
of 53%.
The flow chart of the process is shown in Fig. 1.
Characterization techniques. To examine the
microstructure of the films and determine their thick-
Three types of precursor solutions were used. Solu- ness, we used secondary electron images obtained on a
tion A was prepared using isopropanol, distilled water, JSM-35 CF scanning electron microscope (SEM)
and acetic acid as solvents. Solution B was prepared by equipped with a Link energy-dispersive x-ray
adding ethylene glycol to solution A. Solution C con- microanalysis system (magnifications of up to 10000).
tained methacrylic acid instead of glacial acetic acid. Film thickness was determined on a transverse section.
The three solutions were homogeneous, transparent, We used standard ZAF programs and special programs
INORGANIC MATERIALS Vol. 37
No. 5
2001

5
02
TOMASHPOL’SKII et al.
Table 1. Deposition and heat-treatment conditions (cooling rate, 3°C/min)
Heating rate,
Film no.
Solution Solution concentration, g/l Number of layers
τ, h*
t, °C × τ, h**
°
C/min
t2 × τ
4
1
2
3
4
5
6
A
A
B
B
C
C
4
2
4
2
4
2
7
3
5
3
4
3
4
4
4
4
4
4
650 × 4
650 × 4
650 × 4
650 × 4
650 × 4
650 × 4
2.5
2.5
2.5
2.5
2.5
2.5
t2 × τ
4
7
8
9
A
A
B
B
C
C
4
2
4
2
4
2
7
3
6
4
5
3
6
6
6
6
6
6
750 × 1
750 × 1
750 × 1
750 × 1
750 × 1
750 × 1
1.25
1.25
1.25
1.25
1.25
1.25
1
1
1
0
1
2
t3 × τ
6
13
14
15
16
17
18
A
A
B
B
C
C
4
2
4
2
4
2
7
3
5
3
5
4
8
8
8
8
8
8
850 × 1
850 × 1
850 × 1
850 × 1
850 × 1
850 × 1
0.98
0.98
0.98
0.98
0.98
0.98
Notes: Solution A: Ti(OC H -i) , Zr(C H O ) , Pb(CH COO) · 3H O, CH COOH, i-C H OH, H O; solution B: Ti(OC H -i) ,
3
7
4
5
7
2 4
3
2
2
3
3
7
2
3
7
4
Zr(C H O ) , Pb(CH COO) · 3H O, CH COOH, i-C H OH, H O, OHCH CH OH; solution C: Ti(OC H -i) , Zr(C H O ) ,
5
7
2 4
3
2
2
3
3
7
2
2
2
3
7
4
5 7 2 4
Pb(CH COO) · 3H O, CH =C(CH )COOH, i-C H OH, H O.
3
2
2
2
3
3
7
2
*
Duration of the final drying at 350°C.
*
* Conditions of the final anneal.
for thin layers on substrates. The accelerating voltage loss tangent as functions of temperature, the sample
was from 10 to 20 kV. Concentrations were evaluated was heated in a special furnace. The temperature was
from the TiK , PbL , and ZrL signals. Phase compo- monitored by a Chromel–Alumel thermocouple. The
α
α
α
sition was determined by x-ray diffraction (XRD) with heating rate was 8°C/min, and the cooling rate was
4
−5°C/min. Dielectric hysteresis loop measurements
a DRON-4-07 powder diffractometer (CuK radiation).
α
were made with a Sawyer–Tower circuit. Oscilloscope
traces were used to evaluate the spontaneous polariza-
Dielectric measurements were made on thin-film
capacitors in which the substrate was a base electrode,
and frontside electrodes 1 µm in thickness were depos-
ited by vacuum evaporation (10–3 Pa) of Au from a
tion P , remanent polarization P , and coercive field E .
s
r
c
2
tungsten boat through masks with 1-mm holes. The
EXPERIMENTAL RESULTS
capacitors were mounted in a holder fitted with point
contacts aided with silver paste. In ac resistivity mea-
Each of the 18 PZT films was characterized chemi-
surements, we used a Shch301-1 digital meter. The cally, by XRD, and by SEM. The deviation from the
capacitance and loss tangent were measured with a nominal metals composition (Pb : Ti : Zr = 1 : 0.6 : 0.4)
U7-8 bridge (at 1 kHz, the voltage across the sample was within 6%. All of the films were x-ray pure and had
was 4.3 V). To measure the dielectric permittivity and a perovskite structure (Fig. 2). Most of the films had a
INORGANIC MATERIALS Vol. 37
No. 5 2001

FERROELECTRIC LEAD ZIRCONATE TITANATE FILMS
503
Ti(OC H ) Zr(C H O ) ·10H O Pb(CH C éO) · 3H O
3
7 4
5
7
2 4
2
3
2
2
H O
2
i-PrOH
RCOOH
Preparation of the
precursor solution
[
R– CH –; CH =C(CH )–]
3
2
3
Precursor solution
Dilution
H O
2
i-PrOH
RCOOH
[
R– CH –; CH =C(CH )–]
3 2 3
Working solution
Compressed air (0.5 MPa)
Pt substrates
Deposition cycles
As-deposited films
Heat treatment
Heat-treated films
Au
Vacuum deposition
Thin-film capacitors
Fig. 1. Flow chart of PZT film fabrication on platinum substrates.
pseudocubic cell. In the XRD patterns of the films
annealed at 850°C, the peaks at large angles were split,
indicating a tetragonal distortion.
1
10
Most of the films were characterized by microstruc-
tural examination. Film 1 (solution A) showed heavy
cracking. The surface of film 2 (solution A) was also
cracky and porous. In films 3 and 4 (solution B), the
average crack size was notably smaller, especially in
film 4. Films 5 and 6 (solution C) had a smooth surface
and a crystallite size of 0.2 and 0.6 µm, respectively. On
the surface of film 8, prepared from solution A (2 g/l)
and annealed at 750°C, we observed cracks; the film
consisted of small roundish grains (average grain size
of 0.6 µm). In film 14, prepared under similar condi-
tions but annealed at 850°C, the average grain size was
Ӎ2.2 µm, and the amount of cracking was much smaller.
Films 10 and 16, both prepared from solution B but dif-
fering in annealing temperature, had smooth, crack-
free surfaces, with an average grain size of Ӎ0.6 and
Ӎ1.7 µm, respectively. Films 12 and 18, prepared from
solution C and differing in annealing temperature, had
smooth, crack-free surfaces and sharp grain bound-
aries, with an average grain size of Ӎ1.4 and Ӎ3.4 µm,
211
1
00
2
00
1
11
40
2
20
201
3
01
2
0
60
80
θ, deg
2
Fig. 2. XRD pattern from film 1.
INORGANIC MATERIALS Vol. 37 No. 5 2001

5
04
TOMASHPOL’SKII et al.
RESULTS AND DISCUSSION
Typical ε and P in our films are 1750 and
max
s
2
8
−18 µC/cm , respectively, which is lower than in PZT
ceramics, in which ε attains a few thousands and Ps
attains 45 µC/cm [10]. At the same time, our results
agree with earlier data for PZT films (e.g., ε = 500–
max
2
max
2
1
500 and P = 2–30 µC/cm in [3–11]). The absence of
s
anomalies in the tanδ(T) curves measured at 1 kHz is
likely related to the low frequency. The values E = 42–
c
1
20 kV/cm agree with those reported for PZT films
(
Ec = 60–200 kV/cm) but are higher than those for
1
0 µm
ceramics (Ӎ17 kV/cm) [10]. These results suggest that
the carboxylate process, when optimized further, will
be capable of competing with other chemical routes.
Additional advantages of carboxylates are their good
solubility and the ability to form homogeneous mix-
tures, to wet substrates, and to decompose at relatively
low temperatures without releasing metals or toxic
gases. These properties are inherent in zirconium acety-
lacetonate, tetraisopropyl titanate, and lead acetate. The
use of inorganic compounds, e.g., chlorides or nitrates,
as starting reagents is ineffective, because of the high
decomposition temperatures (>1000°C) and release of
toxic nitrogen and chlorine oxides. To ensure full
replacement of Cl ions in the preparation of tetraisopro-
pyl titanate, we took sodium isopropoxide in excess of
the stoichiometric value. The titanium alkoxide was
separated by threefold extraction with hexane, followed
by liquid–solid separation. The choice of hexane as a
solvent is prompted by the fact that titanium alkoxides
are readily soluble in hexane, and mixtures of hexane,
isopropanol, and titanium alkoxides are easy to sepa-
rate. The low viscosity and low surface tension of hex-
ane are favorable for precipitate separation. Besides,
hexane is nonhygroscopic and prevents hydrolysis of
(
a)
1
µm
(
b)
Fig. 3. SEM micrographs of films (a) 12 and (b) 18.
respectively (Fig. 3). The thickness, composition, and
grain size of the films are listed in Table 2.
The electrical properties of six pore- and crack-free the titanium alkoxide, which was obtained in a yield of
films are summarized in Figs. 4–6 and Table 3.
Ӎ60%, without titanium compounds with chlorine.
ε
tan δ
0
0
0
.9
.8
.7
3
2
1
1
600
200
0.6
1
0
0
0
0
0
.5
.4
.3
.2
.1
0
8
4
00
00
0
2
00 250 300 350 400 450 500
t, °C
2
00 250 300 350 400 450 500
t, °C
Fig. 5. Typical temperature dependences of tan δ at 1 kHz
for the PZT films annealed at (1) 650, (2) 750, and
(3) 850°C.
Fig. 4. Temperature dependences of 1-kHz permittivity for
film 18.
INORGANIC MATERIALS Vol. 37
No. 5 2001

FERROELECTRIC LEAD ZIRCONATE TITANATE FILMS
a) (b) (c)
505
(
P
P
P
Ec
Ec
Ec
(
d)
(e)
(f)
P
P
P
Ec
Ec
Ec
Fig. 6. Dielectric hysteresis loops at 50 Hz for films (a) 6, (b) 8, (c) 12, (d) 14, (e) 16, and (f) 18.
It was also found that, in preparing the precursor
The microstructure was found to be strongly corre-
solution, the sequence in which the reagents are added lated with the concentrations and compositions of the
is important. The solution of zirconium acetylacetonate precursor solutions.At concentrations above 4 g/l, large
in the corresponding carboxylic acid should be added cracks were formed, and spalling was observed. The
to lead acetate dissolved in the appropriate amount of
isopropanol with the addition of one to three drops of a
carboxylic acid in order to prevent hydrolysis. Next, to
this mixture is added titanium isopropoxide. Zirconium
Table 2. Thickness h, chemical composition, and grain size
L of PZT films (perovskite structure)
acetylacetonate should be introduced first because it
reacts with the acid to form a nonhydrolyzable solution
and prevents titanium isopropoxide from hydrolysis
and condensation. If titanium isopropoxide is intro-
duced first, it will react with the acid to form polytitanyl
acetates, which will precipitate. Ethylene glycol should
be added at the final stage, since it reacts with titanium
alkoxides to form an insoluble precipitate. An impor-
tant point in choosing the precursor solution for the
spray pyrolysis process is its ability to be atomized by
an air jet at a pressure of 0.5 MPa and room tempera-
ture. In view of this, the viscosity and surface tension of
the substances for spray pyrolysis are of key impor-
tance. For this reason, we used isopropanol, water, ace-
tic acid, and methacrylic acid as solvents that do not
vaporize at room temperature (tvap from 97 to 163°C).
As a result, the precursor solutions were very stable
under normal conditions and contained high levels of
Pb, Ti, and Zr (45% in terms of oxides) and a minor
amount of carbon, which reduced the probability of
contamination with carboniferous compounds and pre-
vented the formation of a reducing atmosphere in the
course of pyrolysis.
Film no. h, mm
Ti : Zr molar ratio
L, µm
1
2
3
4
5
6
7
8
9
0
1
2
3
1.5
0.5
1.0
0.5
0.8
0.6
1.3
0.6
1.1
0.7
0.9
0.5
1.3
0.6
1.0
0.5
0.9
0.7
0.55 : 0.45
0.58 : 0.42
0.60 : 0.40
0.58 : 0.42
0.60 : 0.40
0.58 : 0.42
0.56 : 0.44
0.57 : 0.43
0.60 : 0.40
0.58 : 0.42
0.54 : 0.46
0.57 : 0.43
0.56 : 0.44
0.54 : 0.46
0.59 : 0.41
0.59 : 0.41
0.57 : 0.43
0.60 : 0.40
–
–
–
–
0.2
0.6
0.5
0.6
0.7
0.6
0.9
1.4
2.0
2.2
1.7
1.7
3.4
3.4
1
1
1
1
14
15
1
1
1
6
7
8
INORGANIC MATERIALS Vol. 37 No. 5 2001

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06
TOMASHPOL’SKII et al.
Table 3. Electrical properties of PZT films
ature to 850°C improves the structural perfection of the
films, and the pseudocubic structure gives way to the
equilibrium, tetragonal structure.
Ps,
µC/cm
Pr,
µC/cm
E ,
kV/cm
c
Film no.
ε20
εTC
2
2
6
8
650 1225
650 1000
600 1350
250 1000
300 1450
250 1750
8
6
5
5
42
44
CONCLUSION
PZT films with Ti : Zr = 0.6 : 0.4 and good ferroelec-
tric properties were prepared by spray pyrolysis of car-
boxylate solutions. The perfection of the films was
found to strongly depend on the composition and con-
centration of the precursor solutions and annealing con-
ditions. The introduction of methacrylic acid and ethyl-
ene glycol into the precursor solution leads to smoother
film surfaces, reduces the amount of cracking and
porosity, and allows the annealing temperature to be
reduced without an adverse effect on the properties of
the films.
12
14
16
18
8
5
120
84
14
13
18
10
10
15
120
107
optimal concentration was 2 g/l. At this concentration,
the films had smooth surfaces without pores or cracks.
At lower concentrations, the microstructure does not
improve, but the process takes more time, and the con-
sumption of the precursor solution increases. The intro-
duction of ethylene glycol raises the solution viscosity,
inhibits vaporization of the solvent from the substrate,
and notably improves the quality of the film surface.
The presence of methacrylic acid reduces the mechan-
ical stress in the deposited layer, which also favors the
formation of pore- and crack-free films. The consecu-
tive deposition of several layers helps obtain stress-free
films uniform in thickness. Our experiments demon-
strate that, all other factors being the same, the porosity
and amount of cracking are lower in multilayer films.
ACKNOWLEDGMENTS
We are grateful to S.S. Korovin for his valuable sug-
gestions and helpful discussions.
REFERENCES
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984.
The optimal substrate temperature in the course of
deposition is 200°C, which ensures sufficiently high
viscosity of the deposited solution and good adhesion
to the substrate. The optimal temperature of the first
stage of annealing is 350°C. At this temperature, the
organic precursors fully decompose, without creating a
reducing atmosphere. Since data on the optimal anneal-
ing temperature are not available in the literature, we
carried out anneals at 650, 750, and 850°C—the most
frequently reported temperatures; the heating rate was
varied from 0.98 to 2.5°C/min. According to chemical
analysis and XRD data, at these heating rates, lead
vaporization and surface cracking are insignificant.
3
. Mansour, S.A., Binford, D.A., and Vest, R.W., The
Dependence of Ferroelectric and Fatigue Behaviour of
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electric and Fatigue Behaviour of PZT Films on Micro-
structure and Orientation, Integr. Ferroelectr., 1992,
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5
. Afanas’ev, V.P., Kaptelov, E.Yu., Kramar, G.P., et al.,
Preparation and Properties of Lead Zirconate Titanate
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6
. Klee, M., Eusmann, R., Waser, R., et al., Processing and
Electrical Properties of Pb(Zr Ti )O (x = 0.2–0.75)
x
1 – x
3
The crystallite size was found to depend not only on
the annealing temperature but also on the compositions
of the precursor solutions. For example, with the solu-
tion containing methacrylic acid, the grain size is
Ӎ0.6 µm after annealing at 650°C, whereas, with acetic
acid, this grain size is attained only by annealing at
Films: Comparison of Metallo-Organic Decomposition
and Sol–Gel Process, J. Appl. Phys., 1992, vol. 72,
pp. 1566–1576.
7
8
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. Preston, K.D. and Haertling, G.H., Microstructural
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. Ozenbaz, M. and Ergin, U., Preparation of Pb(Ti,Zr)O3
Thin Films and Powders by Sol–Gel Process, Ferroelec-
trics, 1996, vol. 186, pp. 219–222.
7
50°C. All other factors being the same, the presence of
methacrylic acid favors grain growth. The average
grain size after annealing at 750°C is 0.6 µm in the film
prepared with the use of acetic acid and 1.4 µm in the
case of methacrylic acid. At 850°C, we obtain, respec-
tively, 2.2 and 3.4 µm. Increasing the annealing temper-
. De Veirman, A.E.M. et al., Transmission Electron
Microscopy Study of PbTiO and PbZr Ti O Films,
3
x
1 – x
3
Mater. Phil. Res. Lab., 1995, pp. 371–379.
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Moscow: Inostrannaya Literatura, 1958.
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INORGANIC MATERIALS Vol. 37 No. 5 2001