Ferroelectrics Material Aspects Part 8 ppt

Ferroelectric-Dielectric Solid Solution and Composites for Tunable Microwave Application

235
He Y. Y., Xu Y. B., Liu T., Zeng C. L., Chen W. P. (2010). Microstructure and Dielectric
Tunable Properties of Ba
0.6
Sr
0.4
TiO
3
-Mg
2
SiO
4
-MgO Composite. IEEE Trans. Ultrason.
Ferroelectr. Freq. Control, Vol.57, No.7, (July 2010), pp. 1505-1512, ISSN 0885-3010
He Y. Y., Xu Y. B., Liu T., Zeng C. L., Chen W. P. (2011). Tunable Dielectric Properties of
BaZr
0.2
Ti
0.8
O
3
-Mg
2
SiO
4
-MgO composite ceramics. J. Alloy. Compd., Vol.509, No.3,
(January 2011), pp. 904-908, ISSN 0925-8388

Kanareykin A., Nenasheva E., Yakovlev V., Dedyk A., Karmanenko S., Kozyrev A., Osadchy
V., Kosmin D., Schoessow P. & Semenov A. (2006). Fast switching ferroelectric
materials for accelerator applications. AIP Conf. Proc., Vol. 877, (2006), pp. 311-319,
ISSN 0094-243X
Kanareykin A., Nenasheva E., Kazakov S., Kozyrev A., Tagantsev A., Yakovlev V. & Jing C.
(2009a). Ferroelectric based technologies for accelerators. AIP Conf. Proc., Vol.1086,
(2009), pp.380-385, ISSN 0094-243X
Kanareykin A., Jing C., Nenasheva E., Schoessow P., Power J. G. & Gai W. (2009b).
Development of a Ferroelectric Based Tunable DLA Structure. AIP Conf. Proc., Vol.
1086, (2009), pp.386-391, ISSN 0094-243X
Lee D. Y., Yoon S. J., Yeo J. H., Nahm S., Paik J. H., Whang K. C. & B. G. Ahn (2000). Crystal
Structure and Microwave Dielectric Properties of La(Mg
1/2
Ti
1/2
)O
3
Ceramics. J. Mat.
Sci. Lett., Vol.19, No.2 , (January 2000), pp. 131-134, ISSN 0261-8028
Maiti T., Guo R. & Bhalla A. S. (2007a). Enhanced Electric Field Tunable Dielectric Properties
of BaZr
x
Ti
1-x
O
3
Relaxor Ferroelectrics. Appl. Phys. Lett., Vol.90, No.18, (April 2007),
pp. 182901, ISSN 0003-6951
Maiti T., Guo R., Bhalla A. S. (2007b). Ferroelectric relaxor behaviour in Ba(Zr
x

Ti
1-x
)O
3
: MgO
composites. J. Phys. D-Appl. Phys.,Vol.40, No.14, (July 2007), pp. 4355-4359, ISSN
0022-3727
Maiti T., Guo R., Bhalla A. S. (2007c). Tailored dielectric properties and tunability of lead
free relaxor Ba(Zr
x
Ti
1-x
)O
3
: MgO composites. Ferroelectr., Vol.361, No.1, (2007), pp.
84-91, ISSN 0015-0193
Maiti T., Guo R., Bhalla A. S. (2008). Structure-Property Phase Diagram of Ba(Zr
x
Ti
1-x
)O
3

System. J. Am. Ceram. Soc., Vol.91, No. 6, (June 2008), pp. 1769–1780, ISSN 0002-7820
Nenasheva, E. A., Kartenko, N. F., Gaidamaka, I. M., Trubitsyna, O. N., Redozubov, S. S.,
Dedyk, A. I.& Kanareykin, A. D. (2010). Low loss microwave ferroelectric ceramics
for high power tunable devices. J. Eur. Ceram. Soc., Vol.30, No.2, (January 2010), pp.
395-400, ISSN 0955-2219
Rao J. B. L., Patel D. P. & Krichevsky V. (1999). Voltage-controlled Ferroelectric Lens Phased
Arrays. IEEE Trans. Antennas Propaga., Vol.47, No.3, (March 1999), pp. 458-468,

ISSN 0018-926X
Romanofsky R. R., Bernhard J. T., Van Keuls F. W., Miranda F. A. & Canedy C. (2000). K-
Band Phased Array Antennas based on Ba
0.60
Sr
0.40
TiO
3
Thin-Film Phase Shifters.
IEEE Trans. Microwave Theory Tech., Vol.48, No.12, (December 2000), pp. 2504-2510,
ISSN 0018-9480
Sengupta L. C. & Sengupta S. (1997). Novel Ferroelectric Materials for Phased Array
Antennas. IEEE Trans. Ultrason. Ferroelectr. Freq. Control, Vol. 44, No.7, (July 1997),
pp. 792-797, ISSN 0885-3010

Ferroelectrics – Material Aspects

236
Sengupta L. C. & Sengupta S. (1999). Breakthrough Advances in Low Loss, Tunable
Dielectric Materials. Mat. Res. Innovat., Vol.2, No.5, (March 1999), pp. 278-282, ISSN
1432-8917
Sherman V. O., Tagantsev A. K. & N. Setter. (2006). Ferroelectric-Dielectric Tunable
Composites. J. Appl. Phys., Vol.99, No.7, (April 2006), pp. 074104, ISSN 0021-8979
Tagantsev A. K., Sherman V. O., Astafiev K. F., Venkatesh J. & N. Setter. (2003). Ferroelectric
Materials for Microwave Tunable Applications. J. Electroceram., Vol.11, No.1-2,
(Sept./Nov. 2003) pp. 5-66, ISSN 1385-3449
Takahashi J., Kageyama K., Fujii T., Yamada T. & Kodaira K. (1997). Formation and
Microwave Dielectric Properties of Sr(Ga
0.5
Ta

0.5
)O
3
-Based Complex Perovskites. J.
Mater. Sci., Mater. in Electron., Vol. 8, No. 2, (April 1997), pp. 79-84, ISSN 0957-4522
Varadan V. K., Varadan V. V., J. F. Kelly & Glikerdas P. (1992). Ceramic Phase Shifters for
Electronically Steerable Antenna Systems. Microwave J., Vol.35, No.1, (January
1992), pp. 116-127, ISSN 0192-6225
Xu Y. B., Liu T., He Y. Y. & Yuan X. (2008). Dielectric Properties of Ba
0.6
Sr
0.4
TiO
3
-
Sr(Ga
0.5
Ta
0.5
)O Solid Solutions. IEEE Trans. Ultrason. Ferroelectr. Freq. Control,
Vol.56, No.11, (November 2008), pp. 2369-2376, ISSN 0885-3010
Xu Y. B., Liu T., He Y. Y. & Yuan X. (2009). Dielectric Properties of Ba
0.6
Sr
0.4
TiO
3
-
La(B
0.5

Ti
0.5
)O
3
(B=Mg, Zn) Ceramics. IEEE Trans. Ultrason. Ferroelectr. Freq. Control,
Vol.56, No.11, (November 2009), pp. 2343-2350, ISSN 0885-3010
Zhi Y., Chen A., Guo R. & Bhalla A. S. (2002). Dielectric Properties and High Tunability of
Ba(Ti
0.7
Zr
0.3
)O
3
Ceramics under dc Electric Field. Appl. Phys. Lett , Vol.81, No.7,
(August 2002), pp.1285–87, ISSN 0003-6951
12
New Multiferroic Materials: Bi
2
FeMnO
6

Hongyang Zhao
1
, Hideo Kimura
1
, Qiwen Yao
1
, Yi Du
2
,

Zhenxiang Cheng
2
and Xiaolin Wang
2

1
National Institute for Materials Science,

2
Institute for Superconducting and Electronics Materials,
University of Wollongong,
1
Japan
2
Australia
1. Introduction
The term “ferroic” was introduced by Aizu in 1970, and presented a unified treatment of
certain symmetry-dictated aspects of ferroelectric, ferroelastic, and ferromagnetic materials.
Ferroelectric materials possess a spontaneous polarization that is stable and can be switched
hysteretically by an applied electric field; antiferroelectric materials possess ordered dipole
moments that cancel each other completely within each crystallographic unit cell.
Ferromagnetic materials possess a spontaneous magnetization that is stable and can be
swithched hysteretically by an applied magnetic field; antiferromagnetic materials possess
ordered magnetic moments that cancel each other completely within each magnetic unit cell.
By the original definition, a single-phase multiferroic material is one that possesses more
than one ‘ferroic’ properties: ferroelectricity, ferromagnetism or ferroelasticity. But the
classification of multiferroics has been broadened to include antiferroic order. Multiferroic
materials, in which ferroelectricity and magnetism coexist, the control of magnetic
properties by an applied electric field or, in contrast, the switching of electrical polarization
by a magnetic field, have attracted a great deal of interest. Now we can classify multiferroic

materials into two parts: one is single-phase materials; the other is layered or composite
heterostructures. The most desirable situation would be to discover an intrinsic single-phase
multiferroic material at room temperature. However, BiFeO
3
is the only known perovskite
oxides that exhibits both antiferromagnetism and ferroelectricity above room temperature.
Thus, it is essential to broaden the searching field for new candidates, which resulted in
considerable interest on designed novel single phase materials and layered or composite
heterostructures.
2. Material designation and characterization
For ABO
3
perovskite structured ferroelectric materials, they usually show antiferromagnetic
order because the same B site magnetic element. While for the A
2
BB
’
O
6
double perovskite
oxides, the combination between B and B
’
give rise to a ferromagnetic coupling. They are
also expected to be multiferroic materials. The ferroelectric polarization is induced by the
distortion which usually causes a lower symmetry. For device application, a large

Ferroelectrics – Material Aspects

238
magnetoelectric effect is expected in the BiFeO

3
and bismuth-based double perovskite
oxides (BiBB
’
O
6
), many of which have aroused great interest like Bi
2
NiMnO
6
, BiFeO
3
-
BiCrO
3
. But far as we know, few researches were focused on Bi
2
FeMnO
6
.
Multiferroic material is an important type of lead-free ferroelectrics. While they usually
showed leaky properties and not well-shaped P-E loops. Dielectricity includes
piezoelectricity, and piezoelectricity includes ferroelectricity. Therefore, it is essential to
characterize the dielectric, piezoelectric and ferroelectric properties together. Firstly we have
designed several multiferroic materials, and then we studied their properties using efficient
techniques which include P-E loop measurement, positive-up-negative-down (PUND) test
and piezoresponse force microscopy (PFM). All the fabricated materials were found to be
multiferroics, so the magnetic properties were also characterized.
2.1 Material designation
Magnetism and ferroelectricity exclude each other in single phase multiferroics. It is difficult

for designing multiferroics with good magnetic and ferroelectric properties. Our interest is
to design new candidate multiferroics based on BiFeO
3
. According to the Goodenough-
Kanamori (GK) rules, many ferromagnets have been designed in double perovskite system
(A
2
BB’O
6
) through the coupling of two B site ions with and without e
g
electrons. Because the
complication of the double perovskite system, there are still some questions about the
violation of the GK rules in some cases and the origin of the ferromagnetism or
antiferromagnetism. Nevertheless, it is believed that the B site superexchange interaction,
the oxygen defects and the mixed cation valences are the important factors in determining
the magnetic properties of the double perovskites. Therefore, the preparation methods and
conditions will show a large influence on the magnetic properties of the fabricated double
peroskites. In order to modify the antiferromagnetic properties of BiFeO
3
, novel single-
phase Bi
2
FeMnO
6
series materials were designed. We have obtained very interesting results
and firstly succeeded in proofing that the designed Bi
2
FeMnO
6

is another promising single-
phase room temperature multiferroic material. Then we designed Nd: BiFeO
3
/YMnO
3
, Nd:
BiFeO
3
/Bi
2
FeMnO
6
to further study the B site superexchange interaction between Fe and
Mn. Surprisingly, they also showed room temperature multiferroic properties. These
exciting results provided us with more confidence in designing devices based on
multiferroic materials. Different preparation methods also show large influence to their
properties. The comparison between the samples of bulk, nano-powder and films is
essential for the understanding of the underlying physics and the development of
ferroelectric concepts.
2.1.1 Bi
2
FeMnO
6
(BFM) and (La
x
Bi
1-x
)
2
FeMnO

6
(LBFM)
BiFeO
3
is a well-known multiferroic material with antiferromagntic with a Neel temperature
of 643 K, which can be synthesized in a moderate condition. In contrast, BiMnO
3
is
ferromagnetic with T
c
= 110 K and it needs high-pressure synthesis. Single phase Bi
2
FeMnO
6

(BFM) ceramics could be synthesized by conventional solid state method as the target.

The
starting materials of Bi
2
O
3
, Fe
3
O
4
, MnCO
3
were weighed according to the molecular mole
ratio with 10 mol% extra Bi

2
O
3
. They were mixed, pressed into pellets and sintered at 800 °C
for 3 h. Then the ceramics were crushed, ground, pressed into pellets and sintered again at
880 °C for 1 h. BFM films were deposited on (100) SrTiO
3
substrate by pulsed laser
deposition (PLD) method at 650°C with 500 ~ 600 mTorr dynamic oxygen.

New Multiferroic Materials: Bi
2
FeMnO
6


239
The stabilization of the single-phase Bi-based perovskites are difficult because of their
tendency of multiphase formation and the high volatility of bismuth. Stabilization can be
facilitated by a partial replacement of Bi
3+
cations by La cations. In addition, LaMn
1-x
Fe
x
O
3

including La
2

FeMnO
6
has been also reported to be an interesting mixed-valence manganite
with perovskite structure. Therefore, La was chosen to partially substitute Bi in Bi
2
FeMnO
6

to stabilization the phase. Polycrystalline 20 mol% La doped Bi
2
FeMnO
6
(LBFM) ceramic
and film were also obtained using the similar preparation methods mentioned above.


Fig. 1. XRD spectra for BFM target and film fabricated on (100) STO (left); XRD for LBFM
film (right).
Figure 1 (left) shows the XRD patterns of the BFM target and the film. Because BiFeO
3
has a
rhombohedral R3c structure whereas BiMnO
3
has a monoclinic structure, it is natural that
the BFM will show a different structure due to the coexist of two transition metal octahedral
with different distortions. Bi et al has calculated three structures of BFM with the space
group of Pm
3 m, R3 and C2. In this work, the bulk BFM target shows a cubic Pm3m
structure and it was indexed using the data from Bi et al. The second phase (Bi
2

Fe
4
O
9
) was
observed in the BFM ceramics, which often appears in the BiFeO
3
ceramics. While the thin
film on the (100) STO substrate fabricated in high oxygen pressure condition shows a single
phase with a bulk-like structure with no traceable impurity. In this study we focused mainly
on the single phase film, because the impurities will have large influences on magnetic
properties and blind the observation of the intrinsic property. As shown in Figure 1 (right),
the LBFM diffraction peaks of (100), (200) and (300) were observed in the XRD pattern. It
indicates the epitaxial growth of LBFM film on the (100) STO substrate. There is no traceable
impurity in the film which is believed to have a bulk-like cubic structure. But there are
unavoidable impurities of bismuth oxides in the LBFM ceramics, which reduces further the
crystalline quality of the ceramic compared with the LBFM film
The Scanning electron microscopy (SEM) was used for the film morphology
characterization. The SEM images of the BFM films were shown in Figure 2. The film on Si
shows fiber shaped morphology with different orientations, as marked as parallel fibers and
inclined fibers. In the contrast, the film on STO substrate shows fibers with almost the same
orientation. It is essential to understand the orientation and anisotropy properties to
optimize and design functional devices. In the previous work, it is proved that BFM on (100)

Ferroelectrics – Material Aspects

240
STO shows large magnetic anisotropy and out-of-plane is the easy magnetization direction.
In this work, we focus mainly on the BFM film fabricated on STO substrates.

Fig. 2. SEM images of BFM film on (a) Si and (b) STO substrate.
2.1.2 Nd: BiFeO
3
/ Bi
2
FeMnO
6
(BFO/BFM)
In our former works, the doping of Nd into BiFeO
3
was found to further improve the
ferroelectric properties. The Bilayered Nd
0.1
Bi
0.9
FeO
3
(Nd: BiFeO
3
)/ BFM films on
Pt/Ti/SiO
2
/Si substrate were fabricated using a PLD system. Nd: BiFeO
3
films were
fabricated at 550 ~ 580 °C with 200 mTorr dynamic oxygen pressure, and the BFM films
were fabricated at 550 ~ 580 °C with ~10
-5
Torr.

Fig. 3. Surface morphology of (a) Nd: BiFeO
3
/Bi
2
FeMnO
6
, (b) Bi
2
FeMnO
6
and (c) Nd: BiFeO
3
.
The surface morphology of the Nd: BiFeO
3
/Bi
2
FeMnO
6
and Nd: BiFeO
3
films were studied
using an atomic force microscope (AFM), as shown in Fig. 3. It can be found that the
corresponding root-mean-square roughness (R
rms
) and the grain size (S) are different: R
rms

(Nd: BiFeO
3
) < R
rms
(Nd: BiFeO
3
/Bi
2
FeMnO
6
) < R
rms
(Bi
2
FeMnO
6
), and S (Nd: BiFeO
3
) < S
(Nd: BiFeO
3
/Bi
2
FeMnO
6
) < S (Bi
2
FeMnO
6
). Fig. 3 (a) revealed the morphology of the Nd:

BiFeO
3
film on the Bi
2
FeMnO
6
/Pt/Ti/SiO
2
/Si, which indicated that Nd: BiFeO
3
had a larger
growth rate on Bi
2
FeMnO
6
than on Pt/Ti/SiO
2
/Si substrate.
2.1.3 Nd: BiFeO
3
/YMnO
3
(BFO/YMO)
Another well-studied muliferroic material YMnO
3
was chosen to from the Nd:
BiFeO
3
/YMnO
3

(BFO/YMO) heterostructure. The hexagonal manganite YMnO
3
, which
shows an antiferromagnetic transition at T
N
=75 K and a ferroelectric transition at T
C
=913

New Multiferroic Materials: Bi
2
FeMnO
6


241
K, is one of the rare existing single phase multiferroics. The hexagonal YMnO
3
is
ferroelectric, but the orthorhombic YMnO3 is not ferroelectric. The (111) planes are special
for BiFeO
3
, the Fe spins are coupled ferromagnetically in the pseudocubid (111) planes
and antiferromagnetically between neighbouring (111) planes. In this study, the
BFO/YMO film was fabricated on (111) Nb: SrTiO
3
(STO) substrate the Nd: BiFeO
3
and
YMnO

3
ceramics were synthesized by conventional solid state method as the targets. The
Nd: BiFeO
3
/YMnO
3
(BFO/YMO) film were deposited on (111) STO substrate using a
pulsed laser deposition (PLD) system at 530-700°C with 10
-3
~10
-1
Torr dynamic oxygen.
The two separate targets were alternately switched and the films were obtained through a
layer-by-layer growth mode. After deposition, the film was annealed at the same
condition for 15 minutes and then cooled to room temperature. In this report, the film
comprised of four layers: (1) Nd: BiFeO
3
(2) YMnO
3
(3) Nd: BiFeO
3
and (4) YMnO
3
. The
deposition time of each layer is 10 min.
2.2 Ferroelectric characterization
The methods and special techniques for materials with weak ferroelectric properties will be
explained and summarized in detail. For typical ferroelectric materials, it is easy to identify
their ferroelectricity because we could obtain well-shaped ferroelectric polarization
hysteresis loops (P-E loop). However, as the definition of ferroelectricity is strict, it is

difficult to characterize weak ferroelectricity and to check whether it has ferroelectric
property or not. Here we will introduce our experience for characterization and
identification of such materials.
2.2.1 P-E loop measurement
For the P-E loop measurment, Pt upper electrode with an area of 0.0314 mm
2
were deposited
by magnetron sputtering through a metal shadow mask. The ferroelectric properties were
measured at room temperature by an aixACCT EASY CHECK 300 ferroelectric tester. Figure
4 shows the ferroelectric hysteresis loops of the Nd: BiFeO
3
/Bi
2
FeMnO
6
film, the upper inset
shows the polarization fatigue as a function of switching cycles up to 10
8
and the lower inset
shows frequency dependence of the real part of dielectric permittivity. The remnant
polarization P
r
is 54 μC/cm
2
and E
c
is 237 kV/cm. Some anomalies were observed in the P-E
loop: the loop is asymmetry and the polarization decreased as the increasing of the electric
field. It can be caused by many effects but some of them can be neglected like the
macroscopic electrode influence and nonuniform polarization on the surface of the film. We

consider there are two main reasons. The film is insulating so there is no movable carriers to
balance the bound charge. Therefore, the polarization gradient will be arisen in the film and
induced the depolarization field. In addition, there are inhomogeneous domains with
different coercivity in the film, some of which are difficult to switch with applied field.
Evidence can also be seen in the fatigue results which showed that the polarization
increased with the increasing of the switching cycles. The fatigue can be caused by domain
nucleation, domain wall pinning due to space charges or oxygen vacancies, interface
between electrode and film, thermodynamic history of the sample and so on. For the
unusual profile of fatigue (polarization increased with that the increasing of switching
cycles), we consider the different domain wall played important roles during the
polarization reversal. The dielectric properties were measured using a HP4248 LCR meter.
Frequency dependence of the real part of the permittivity was measured at room

Ferroelectrics – Material Aspects

242
temperature. There is a notable increase at low frequencies (as shown in the lower inset of
Fig. 4). In such bilayered films, it is believed that there are space charges at the interface
between the two layers of the Nd: BiFeO
3
and Bi
2
FeMnO
6
which will affect the ferroelectric
properties.

Fig. 4. Ferroelectric hysteresis loops of Nd: BiFeO
3
/BFM film, the polarization fatigue as a

function of switching cycles (upper inset) and the frequency dependence of the real part of
dielectric permittivity (lower inset).
2.2.2 PUND: positive-up-negative-down test
As the definition of ferroelectricity is strict, a not-well-saturated loop might not be a proof of
ferroelectricity, we have also measured the so-called positive-up-negative-down (PUND)
test for Nd: BiFeO
3
/ BFM film. The applied voltage waveform is shown in Fig. 5. The
switching polarization was observed using the triangle waveform as a function of time as
shown in Fig. 5.


Fig. 5. (a) PUND waveform and (b) corresponding switching polarization.

New Multiferroic Materials: Bi
2
FeMnO
6


243
2.2.3 PFM characterization for BFM and LBFM film
Until now there is no report about the ferroelectric properties of BFM because the difficulty
of obtaining well-shaped polarization hysteresis loops. Thus, it is important to study and
understand the ferroelectric properties and leakage mechanisms in the BFM system. The
emerging technique of piezoresponse force microscopy (PFM) is proved to be a powerful
tool to study piezoelectric and ferroelectric materials in such cases and extensive
contributions have been published. In PFM, the tip contacts with the sample surface and the
deformation (expansion or contraction of the sample) is detected as a tip deflection. The
local piezoresponse hysteresis loop and information on local ferroelectric behavior can be

obtained because the strong coupling between polarization and electromechanical response
in ferroelectric materials.

In the present study, we attempts to use PFM to study the
ferroelectric/piezoelectric properties in BFM and LBFM thin films. PFM response was
measured with a conducting tip (Rh-coated Si cantilever, k~1.6 N m
-1
) by an SII
Nanotechnology E-sweep AFM. PFM responses were measured as a function of applied DC
bias (V
dc
) with a small ac voltage applied to the bottom electrode (substrate) in the contact
mode, and the resulting piezoelectric deformations transmitted to the cantilever were
detected from the global deflection signal using a lock-in amplifier.


Fig. 6. (a) OP PFM image polarized by ±10 V and (b) which curve is associated with the left
y-axis and which one is with the right y-axis as well as Fig.7 (c)local piezoresponse
hysteresis loop of BFM film.
In Figure 6 (a), the smaller part A marked in red square was firstly poled with -10 V DC bias,
and the total area of 3×3 µm
2
was subsequently poled with +10 V DC bias. The domain
switching in red square area was observed, while another similar area beside ‘A’ was also
observed and marked as B in black square. It may be because the expansion of ferroelectric
domain under the DC bias. To further understand its ferroelectric nature, the local
piezoelectric response was measured with a DC voltage from -10 V to 10 V applied to the
sample. The typical “butterfly” loop was observed but it is not symmetrical, and it is not
well-shaped due to the asymmetry of the upper and bottom electrodes. According to the
equation d

33
=Δl/V, where Δl is the displacement, the effective d
33
could be calculated. At the
voltage of -10 V, the sample has the maximum effective d
33
of about -28 pm/V.

Ferroelectrics – Material Aspects

244
Fig. 7. (a) OP PFM image, (b) IP PFM image polarized by ±10 V and (c) local piezoresponse
hysteresis loop of LBFM film.
Figure 7 shows the OP (a) and IP (b) PFM images of the LBFM film which was also
fabricated on (100) STO substrate. Under ±10 V DC bias, PFM images were observed in
the scans of the LBFM film, demonstrating that polarization reversal is indeed possible
and proving that the LBFM film is ferroelectric at room temperature. At the voltage of 10
V, the sample has a maximum effective d
33
of about 32 pm/V. The LBFM film shows
improved piezoelectric and ferroelectric properties compared to the BFM film, indicating
that through the doping or changing of other conditions, the ferroelectric property of BFM
system could be improved as in the BiFeO
3
. The domain boundary is very clear and
regular in LBFM, while in BFM it is obscure and expanded over the poled area. The
propagation of domain wall is strongly influenced by local inhomogeneities (e.g. grain
boundaries) and stress in polycrystalline ferroelectrics, which results in strong irregularity
of the domain boundary. After the La substitution, it is assumed that the crystallization is
better both in ceramics and films.

2.3 Magnetic characterization for BFM film
BFM is considered to be a new multiferroic material, it is important to study their magnetic
properties. Magnetic properties were measured using the commercial Quantum Design
SQUID magnetometer (MPMS). In the following, we will discuss the XPS measurements, the
magnetization hysteresis loops, and the ZFC and FC courves for the BFM film fabricated on
the (100) STO susbtrate.

New Multiferroic Materials: Bi
2
FeMnO
6


245
2.3.1 XPS measurements
The valance states of Fe and Mn in the BFM film were carried out using PHI Quantera SXM
x-ray photoelectron spectrometer (XPS). Figure 8 shows the Fe 2p and Mn 2p photoelectron
spectra of BFM film. It was reported that Fe 2p photoelectron peaks from oxidized iron are
associated with satellite peaks, which is important for identifying the chemical states. The
Fe
2+
and Fe
3+
2p
3/2
peaks always show the satellite peaks at 6 eV and 8 eV above the
principal peaks at 709.5 eV and 711.2 eV, respectively. In Figure 8 (a), the satellite peaks
were found just 8 eV above the 2p
3/2
principal peak. It indicates that in this system Fe is

mainly in the Fe
3+
state. Figure 8 (b) shows typical XP spectra of Mn 2p. There are two main
peaks corresponding to the 2p
1/2
and 2p
3/2
peaks, respectively. The peaks with higher
binding energy above the main peaks as well as the splitting of the main peaks were
observed in the film. It indicates the existence of Mn
2+
. Such shake-up satellite peaks were
considered to be a typical behavior in Mn
2+
systems.


Fig. 8. (a) Fe 2p and (b) Mn 2p XP spectra for BFM film on (100) STO
2.3.2 Magnetic hysteresis loops
For the BFM thin films, different substrates of Pt/Ti/SiO
2
/Si and STO were used and
different fabrication conditions were attempted. Some unavoidable impurities and
different structures were observed for the films on Pt/Ti/SiO
2
/Si substrates. In order to
discuss the origin of the ferromagnetic properties in BFM film, films on (100) STO were
used for the study of magnetic properties. Figure 9 (a) shows the hysteresis loops
measured at different temperatures. There is no significant change in the loop width from
5 K to 300 K. Figure 9 (b) shows the in-plane and out-of-plane magnetic field dependence

of magnetization measured at 5 K. The film shows stress induced anisotropy from
film/substrate mismatch which is an evidence of a Jahn-Teller effect and the out-of-plane
is the easy magnetization direction. However, we observed experimentally that Mn shows
multiple valence states despite the higher stability of the compound only containing Mn
3+

ions in the film. It is possibly because the Mn
2+
and Mn
4+
cations could decrease the Jahn-
Teller effect from Mn
3+
in the film, which may result in less lattice distortion caused
by Mn
3+
.

Ferroelectrics – Material Aspects

246

Fig. 9. Magnetic hysteresis loops of BFM film. (a) at different temperatures and (b) with
magnetic field applied parallel and perpendicular to the sample plane
2.3.3 ZFC and FC measurements
Figure 10 shows temperature dependence of out-of-plane magnetization measured under
zero-field-cooling (ZFC) and field-cooling (FC) conditions and in different magnetic fields.
Similar to BiFeO
3
(with a cusp at around 50 K) a spin-glass-like behavior below 100 K was

observed with the cusp at about 25 K. As shown in Figure 10 (a), the irreversibility below
100 K between FC curve and ZFC curve is clear with applied field of 500 Oe and 1000 Oe,
but it was suppressed in higher field above 5 kOe and shift to much lower temperature,
which is a typical behavior of spin glass ordering. Above the temperature of 100 K for spin-
glass-like behavior appearing, another magnetic transition at about 360 K was observed in
Figure 10 (b). Hysteresis behavior disappears above this temperature as shown in Figure 9
(a), which indicated an antiferromagnetic transition happens at this temperature.


Fig. 10. ZFC and FC results of BFM film.
The film on STO was fabricated at higher temperature and higher oxygen pressure resulted
in a good crystalline quality, less oxygen vacancies and no traceable impurity. BFM film on

New Multiferroic Materials: Bi
2
FeMnO
6


247
(100) STO made under these improved fabrication conditions will display enhanced
magnetic properties. The magnetizations of BFM film at 1 T are estimated from M-H loops
as 0.30 µ
B
, 0.26 µ
B
, 0.23 µ
B
, 0.21 µ
B

and 0.19 µ
B
per B site ion at temperatures of 5 K, 50 K, 100
K, 300 K and 360 K, respectively. These values are smaller than 0.5 µ
B
for antiferromagnetic
ordering of Fe
3+
and Mn
3+
, which is probably due to the local inhomogeneities in the film
and some antisite disorders in the B-site. Actually the magnetic moment should be much
larger than 0.5 µ
B
at per B site if Mn and Fe are homogenously distributed, because both
Fe
3+
-O
2-
-Mn
2+
and Fe
3+
-O
2
-Mn
3+
in 180-degree bonds will produce orthoferrite, i.e. canted
antiferromagnet and result in a larger moment based on the Goodenough-Kanamori rules.
Therefore, in our films the arrangements of Mn

3+
-O-Mn
3+
and Fe
3+
-O-Fe
3+
with both
resulting strong antiferromagnetism will have significant contribution to the observed
magnetic properties. Due to Mn
3+
(3d
4
) is a Jahn-Teller ion, a strong Jahn-Teller effect will
cause significant structure distortion in BFM film and produce the anisotropy effects. An
external stress originating from BFM/STO lattice mismatches can greatly enhance the
resulting cooperative strain and enhance the magnetic anisotropy. However, the multiple
valence states of Mn ions in the film, the Mn
2+
and Mn
4+
can decrease the lattice distortion
caused by Mn
3+
and result in better lattice matching between film/substrate and decrease
the anisotropic property. All of the curves shown here are corrected from the diamagnetic
background of the STO substrate. The M-H and M-T data of the (100) STO substrate were
obtained using the same system.
3. Conclusion
The piezoelectric/ferroelectric and magnetic properties of BFM series materials, which

include BFM film and ceramic, LBFM film and ceramic, Nd: BiFeO
3
/ BFM film and Nd:
BiFeO
3
/YMnO
3
film, were studied in detail. In this chapter, we mainly focus on the BFM
film. It was proved that stabilization can be facilitated by a partial replacement of Bi
3+

cations by La cations. The film and ceramic showed different properties and after La doping,
both ferroelectric and magnetic properties were improved.
The piezoelectric/ferroelectric properties of BFM series materials have been studied using
different methods, including P-E loop measurement, positive-up-negative-down (PUND)
test and piezoresponse force microscopy (PFM). PFM was used to investigate the domain
configurations and local piezoresponse hysteresis loops for BFM and LBFM films. The PFM
images confirmed that the domain could be poled and switched in both films. The clearer
domain boundary in the LBFM film indicated better crystallization and ferroelectric
properties compared to the BFM film. The local butterfly-type piezoresponse hysteresis
loops were obtained. All the observations suggest that BFM and LBFM films are room
temperature ferroelectric materials. Improved ferroelectric properties are expected in the
BFM system through the adjustment of doping ions and fabrication conditions to obtain
promising multiferroic candidates.
The magnetic hysteresis loops and temperature dependent magnetization were also studied.
BFM film with good crystalline quality and with enhanced magnetic properties was
obtained on (100) SrTiO
3
substrate through the optimization of the fabrication conditions.
Similar to BiFeO

3
, the spin-glass-like behavior is observed below 100 K with the cusp at 25
K. The ZFC and FC curves measured from 2 K to 400 K show a kink at around 360 K and
hysteresis disappears at 360 K, revealing a antiferromagnetic transition at this temperature.
The observed anisotropy effects were caused by Jahn-Teller ions of Mn
3+
. Mn tends to form

Ferroelectrics – Material Aspects

248
multiple valence states as in the film it is possibly because the Mn
2+
and Mn
4+
cations
decrease the Jahn-Teller effect caused by Mn
3+
.
Several questions in weak ferroelectric materials still remained to be anwsered. We wish to
share these questions and have more discussion based on the as-designed materials for
further development of such ferroelectrics.
4. Acknowledgment
The authors gratefully acknowledge Dr. Shigeki Nimori, Dr. Hideaki Kitazawa, Dr. Minora
Osada, Dr. Baowen Li of NIMS, Prof. Huarong Zeng of Shanghai Institute of Ceramics for
the valuable discussions and Dr. Hideo Iwai of NIMS for the XPS measurement. This work
was supported in part by grants from JSPS and ARC under the Japan-Australia Research
Cooperative Program, and Grant-in-Aid for JSPS Fellows (21-09608).
5. References
Lines, M.E. & A.M. Glass, (1977), Principles and applications of ferroelectrics and related

materials, Oxford University press, ISBN 0198512864
Eerenstein,W.; Mathur, N.D. & Scott, J.F. (2006). Multiferroic and magnetoelectric materials.
Nature,Vol. 442, No. 17, (August 2006), pp. 759-765, ISSN 0028-0836
Dass, R. I.; Yan, J. Q. & Goodenough, J. B. (2003). Oxygen stoichiometry, ferromagnetism
and transport properties of La
2-x
NiMnO
6+δ
, Phys. Rev. B Vol. 68, pp. 064415-064427,
ISSN 1098-0121
Dass, R.I. & Goodenough, J.B. (2003). Multiple magnetic phases of La
2
CoMnO
6-δ

(0<~δ<~0.05), Phys. Rev. B Vol.67, pp. 014401.1-014401.9, ISSN 1098-0121
Blasse, G. (1965). Ferromagnetic interactions in non-metallic perovskites, J. Phys. Chem.
Solids, Vol. 26, No. 12, pp. 1969-1971, ISSN 0022-3697
Azuma, M.; Takata, K.; Saito, T.; Ishiwata, S.; Shimakawa, Y. & Takano, M. (2005). A
Designed New Ferromagnetic Ferroelectric Bi
2
NiMnO
6
, J. Am. Chem. Soc. Vol. 1, pp.
8889-8892, ISSN 0002-7863
Rogado, N.S.; Li, J.; Sleight, A.W. & Subramanian, M.A. (2005). Magnetocapacitance and
Magnetoresistance Near Room Temperature in a Ferromagnetic Semiconductor:
La
2
NiMnO

6
, Adv. Mater. Vol. 17, pp. 2225-2227, ISSN 1501-4095
Wang, J.; Neaton, J. B.; Zheng, H.; Nagarajan, V.; Ogale, S. B.; Liu, B.; Viehland, D.;
Vaithyanathan, V.; Schlom, D. G.; Wuttig, M. & Ramesh, R. (2003). Epitaxial BiFeO3
Multiferroic Thin Film Heterostructures, Science Vol. 299, (March 2003), pp. 1719-
1722, ISSN 0036-8075
Atou, T.; Chiba, H.; Ohoyama, K.; Yamaguchi, Y. & Syono, Y. (1999). Structure
Determination of Ferromagnetic Perovskite BiMnO
3
, J. Solid State Chem. Vol. 145,
No. 2, pp. 639-642, ISSN 0022-4596
Kimura, T.; Kawamoto, S.; Yamada, I.; Azuma, M.; Takano, M. & Tokura, Y. (2003).
Magnetocapacitance effect in multiferroic BiMnO
3
, Phys. Rev. B Vol. 67 (R), (May
2003), pp. 180401-180404, ISSN 1098-0121
Fujino, S.; Murakami, M.; Lim, S. H.; Salamanca-Riba, L.G.; Wuttig, M. & Takeuchi, I. (2007).
Multiphase growth in Bi-Mn-O thin films, J. Appl. Phys. Vol. 101, No. 1, pp. 013903,
ISSN 0021-8979

New Multiferroic Materials: Bi
2
FeMnO
6


249
De, K.; Ray, R.; Panda, R.N.; Giri. S.; Nakamura, H. & Kohara, T. (2005). The effect of Fe
substitution on magnetic and transport properties of LaMnO
3

, J. Magn. Magn.
Mater. Vol. 288, pp. 339-346, ISSN 0304-8853
De, K.; Thakur, M.; Manna, A. & Giri, S. (2006). Unusual glassy states in LaMn
0.5
Fe
0.5
O
3
:
Evidence of two distinct dynamical freezing processes, J. Appl. Phys. Vol. 99, No. 1,
pp. 013908, ISSN 0021-8979
Tong, W.; Zhang, B.; Tan, S. & Zhang, Y. (2004). Probability of double exchange between Mn
and Fe in LaMn
1−x
Fe
x
O
3
, Phys. Rev. B Vol. 70, (July 2004), pp. 014422, ISSN 1098-0121
Gajek, M.; Bibes, M.; Fusil, S.; Bouzehouane, K.; Fontcuberta, J.; Barthelemy, A. & Fert, A.
(2007). Tunnel junctions with multiferroic barriers, Nat. Mater. Vol. 6, pp. 296-302,
ISSN 1476-1122
Gajek, M.; Bibes, M.; Wyczisk, F.; Varela, M.; Fontcuberta, J. & Barthelemy, A. (2007).
Growth and magnetic properties of multiferroic La
x
Bi
1−x
MnO
3
thin films, Phys. Rev.

B Vol. 75, (May 2007), pp. 174417, ISSN 1098-0121
Langenberg, E.; Varela, M.; Garcia-Cuenca, M.V.; Ferrater, C.; Polo, M.C.; Fina, I.; Fabrega,
L.; Sanchez, F. & Fontcuberta, J. (2009). Epitaxial thin films of (Bi
0.9
La
0.1
)
2
NiMnO
6

obtained by pulsed laser deposition, J. Mag. Mag. Mat. Vol. 321, No. 11, pp. 1748-
1753, ISSN 0304-8853
Marin, L.W.; Crane, S.P.; Chu, Y-H.; Holcomb, M.B.; Gajek, M.; Huijben, M.; Yang, C-H.;
Balke, N. & Ramesh, R. (2008). Multiferroics and magnetoelectrics: thin films and
nanostructures, J. Phys.: Condens. Matter Vol. 20, No. 43, pp. 434220, ISSN 1742-6588
Yakel, H.L.; Koehler, W.C.; Bertaut, E.F.& Forrat, E.F. (1963). On the crystal structure of the
manganese(III) trioxides of the heavy lanthanides and yttrium, Acta Crystallogr.
Vol. 16 pp. 957-962, ISSN 0365-110X
Dho, J.; Leung, C.W.; MacManus-Driscoll, J.L. & Blamire, M.G. (2004). Epitaxial and oriented
YMnO
3
film growth by pulsed laser deposition, J. Crystal Growth Vol. 267, No. 3-4,
pp. 548-553, ISSN 0022-0248
Ruette, B.; Zvyagin, S.; Pyatakov, A.P.; Bush, A.; Li, J.F.; Belotelov, V.I.; Zvezdin, A.K. &
Viehland, D. (2004). Magnetic-field-induced phase transition in BiFeO
3
Cycloidal to
homogeneous spin observed by high-field electron spin resonance: order, Phys.
Rev. B Vol. 69, (February 2004), pp. 064114, ISSN 1098-0121

Jang, H.W.; Ortiz, D.; Baek, S.; Foliman, C.M.; Das, R.R.; Shafer, P.; Chen, Y.B.; Nelson, C.T.;
Pan, X.Q.; Ramesh, R. & Eom, C. (2009). Domain Engineering for Enhanced
Ferroelectric Properties of Epitaxial (001) BiFeO Thin Films, Adv. Mater. Vol. 21, No.
7, pp. 817-823, ISSN 1501-4095
Wu, J.G.; Kang, G.Q.; Liu H. J. &Wang, J. (2009). Ferromagnetic, ferroelectric, and fatigue
behavior of (111)-oriented BiFeO
3
/(Bi
1/2
Na
1/2
)TiO
3
lead-free bilayered thin films,
Appl. Phys. Lett. Vol. 94, No. 17, pp. 172906, ISSN 0003-6951
Scott, J.F. (2008). Ferroelectrics go bananas, J. Phys: Condens. Matter, Vol. 20, No. 2, pp.
021001, ISSN 1742-6588
Scott, J. F. (2000). Ferroelectric memories, Springer, ISBN 978-3-540-66387-4, Berlin
Balke, N.; Bdikin, I.; Kalinin, S.V. & Kholkin, A.L. (2009). Electromechanical Imaging and
Spectroscopy of Ferroelectric and Piezoelectric Materials: State of the Art and
Prospects for the Future, J. Am. Ceram. Soc., Vol. 92, No. 8, pp. 1629-1647, ISSN
1551-2916
Kalinin, S.V. & Bonnell, D.A. (2001). Local potential and polarization screening on
ferroelectric surfaces, Phys. Rev. B Vol. 63, (March 2001), pp. 125411, ISSN 1098-0121
Kalinin, S.V.; Rodriguez, B.J.; Borisevich, A.Y.; Baddorf, A.P.; Balke, N.; Chang, H.J.; Chen,
L.Q.; Choudhury, S.; Jesse, S.; Maksymovych, P.;. Nikiforov, M.P & Pennycook, S.J.

Ferroelectrics – Material Aspects

250

(2010). Defect-Mediated Polarization Switching in Ferroelectrics and Related
Materials: From Mesoscopic Mechanisms to Atomistic Control Adv. Mater. Vol. 22,
No. 3, pp. 314-322, ISSN 1501-4095
Shafer, P.; Zavaliche, F.; Chu, Y.H.; Yang, P.L.; Cruz, M.P. & Ramesh, R. (2007). Planar
electrode piezoelectric force microscopy to study electric polarization switching in
BiFeO
3
, Appl. Phys. Lett. Vol. 90, pp. 202909, ISSN 0003-6951
Catalan, G.; Bea, H.; Fusil, S.; Bibes, M.; Paruch, P.; Barthélémy, A. & Scott, J.F. (2008).
Fractal Dimension and Size Scaling of Domains in Thin Films of Multiferroic
BiFeO
3
, Phy. Rev. Lett. Vol. 100, No. 2, pp. 027602, ISSN 0031-9007
Keeney, L.; Zhang, P.F.; Groth, C.; Pemble, M.E. & Whatmore, R.W. (2010). Piezoresponse
force microscopy investigations of Aurivillius phase thin films, J. Appl. Phys. Vol.
108, pp. 042004, ISSN 0021-8979
Cheng, Z.X.; Wang, X.L.; Dou, S. X.; Kimura, H. & Ozawa, K. (2008). Improved ferroelectric
properties in multiferroic BiFeO
3
thin films through La and Nb codoping, Phys. Rev.
B Vol. 77, pp. 092101, ISSN 1098-0121
Cheng, Z.X.; Li, A.H.; Wang, X.L.; Dou, S.X.; Ozawa, K.; Kimura, H.; Zhang, S.J. & Shrout,
T.R. (2008). Structure, ferroelectric properties, and magnetic properties of the La-
doped bismuth ferrite, J. Appl. Phys. Vol. 103, pp. 07E507, ISSN 0021-8979
Zhao, H.Y.; Kimura, H.; Cheng, Z.X.; Wang, X.L. &Nishida, T. (2009). Room temperature
multiferroic properties of Nd:BiFeO
3
/Bi
2
FeMnO

6
bilayered films, Appl. Phys. Lett.
Vol. 95, No. 23, pp. 232904, ISSN 0003-6951
Zhao, H.Y.; Kimura, H.; Cheng, Z.X.; Wang, X.L.; Ozawa, K. & Nishida, T. (2010). Magnetic
characterization of Bi
2
FeMnO
6
film grown on (100) SrTiO
3
substrate Phys. Status
Solidi RRL Vol. 4, No. 11, pp. 314, ISSN 1862-6270
Zhao, H.Y.; Kimura, H.; Cheng, Z.X.; Wang, X.L.; Ozawa, K. & Nishida, T. (2010). Magnetic
properties of La doped Bi
2
FeMnO
6
ceramic and film, J. App. Phys. Vol. 108, pp.
093903, ISSN 0021-8979
Du, Y.; Cheng, Z.X.; Dou, S.X.; Wang, X.L.; Zhao, H.Y. & Kimura, H. (2010). Magnetic
properties of Bi
2
FeMnO
6
: A multiferroic material with double-perovskite structure,
Appl. Phys. Lett. Vol. 97, pp. 122502, ISSN 0003-6951
Wandelt, C. (1982). Photoemission studies of adsorbed oxygen and oxide layers, Surf. Sci.
Pep. Vol. 2, No. 1, pp. 1-121, ISSN 0127-5729
Beyreuther, E.; Grafstrom, S.; Thiele, L.M. & Dorr, K. (2006). XPS investigation of Mn
valence in lanthanum manganite thin films under variation of oxygen content,

Phys. Rev. B Vol. 73, No. 15, pp. 155425, ISSN 1098-0121
Wang L. & Gao, J. (2009). Electronic structures and Hall effect in low-doped La
0.9
Hf
0.1
MnO
3

epitaxial films, J. Appl. Phys. Vol. 105, pp. 07E514, ISSN 0021-8979
Dionne, G.F. (1979). Origin of the magnetostriction effects from Mn
3+
, Co
2+
, and Fe
2+
ions in
ferrimagnetic spinels and garnets, J. Appl. Phys. Vol. 50, pp. 4263, ISSN 0021-8979
Dionne, G.F. (2007). Evidence of magnetoelastic spin ordering in dilute magnetic oxides, J.
Appl. Phys. Vol. 101, pp. 09C509, ISSN 0021-8979
Dionne G.F. & Kim, H-S. (2008). J. Appl. Phys. Vol. 103, pp. 07B333, ISSN 0021-8979
Bi, L.; Taussig, A.R.; Kim, H-S.; Wang, L.; Dionne, G.F.; Bono, D.; Persson, K.; Ceder, G.&
Ross, C.A. (2008). Structural, magnetic, and optical properties of BiFeO
3
and
Bi
2
FeMnO
6
epitaxial thin films: An experimental and first-principles study, Phys.
Rev. B Vol. 78, No. 10, pp. 104106, ISSN 1098-0121

Singh, M.K.; Prelier, W.; Singh, M.P.; Katiyar, R. S. &. Scott, J. F (2008). Spin-glass transition
in single-crystal BiFeO
3
,Phys. Rev. B Vol. 77, No. 14, pp. 144403, ISSN 1098-0121
13
Lead Titanate-Based Nanocomposite:
Fabrication, Characterization and Application
and Energy Conversion Evaluation
Walter Katsumi Sakamoto
1
, Gilberto de Campos Fuzari Jr
1
,
Maria Aparecida Zaghete
2
and Ricardo Luiz Barros de Freitas
3

1
Faculdade de Engenharia, UNESP – Univ. Estadual Paulista – Campus de Ilha Solteira,
Depto de Física e Química, Grupo de Polímeros,

2
Instituto de Química, Universidade Estadual Paulista – UNESP,
3
Faculdade de Engenharia, UNESP – Univ. Estadual Paulista – Campus de Ilha Solteira,
Departamento de Engenharia Elétrica
Brazil
1. Introduction
Within the past 5 decades the use of ferroelectric composite made of ferroelectric ceramic

immersed in polymer matrix has expanded significantly. One of the goals to embedding
ceramic grains within a polymer matrix to form a 0-3 composite film is to combine the
better properties of each phase, such as high piezoelectric activity of the ceramic and the
mechanical resistance, formability and flexibility of the polymer, also because the 0-3
composite is the easier and cheaper way to fabricate this alternative electro-active
material.
Some desirable properties for composite materials are: high piezoelectric charge and
voltage coefficients for passive piezoelectric devices; large piezoelectric charge coefficient
and low relative dielectric constant for active devices. Furthermore, the poling process of
the composite film should be effective, which impose the composite must be
homogeneously fabricated, i.e., the composite film should have uniformly dispersed
ceramic grain.
Piezoelectric devices have some specific advantages over electromagnetic such as suitability
to be miniaturized; there is no need of magnetic shielding; it is more efficient at least in the
lower power range. There is a very large range of applications of piezoelectric materials,
either as sensing element or as actuators. One of the most recent interests on piezoelectric
materials is energy harvesting, converting mechanical to electrical energy. The aim of this
research area is to provide clean energy attending the needs of the world in the fight against
pollution.
Conventional ferroelectric materials such as lead zirconate titanate (PZT) [Jaffe 1969, Ren
2003, Klee 2010], modified lead titanate [Wang 2000, Chu 2004, Pontes 2001] and
ferroelectric polymers [Lovinger 1983, Kawai 1969, Bauer 2000] have been used in
applications which use either piezo or pyroelectric properties. Concerned to the

Ferroelectrics – Material Aspects

252
piezoelectric applications, they have been employed in a large range of transducers such as
for hydrophone [Lau 2002, Boumchedda 2007], dynamic strain measurements [Soman 2011],
medical ultrasound [Zhang 2006, Muralt 2004] and non-destructive evaluation of structures

[Brown 1996, Ciang 2008, Edwards 2006].
On the pyroelectric applications, ferroelectric materials can be used as infrared detectors
[Sosnin 2000, Huang 2002, Guggilla 2006] and X-ray intensity measurements [De Paula 2005,
Pontes 2010, De Carvalho 1997]. Using the pyroelectric property of the sensing element,
KUBE Electronics AG (Switzerland) has developed a flame detection and gas analysis device
[www.kube.ch].
Ferroelectric ceramics have high piezo and pyroelectric properties but, for some
applications, their poor mechanical properties and the mismatch of the acoustic impedance
with water and human tissue restrict their usage. On the other hand, ferroelectric polymers
have mechanical flexibility and formability but their piezo and pyroelectric activity are low.
To overcome these problems composite materials made of ferroelectric ceramic and polymer
have been investigated as an alternative material which combine the better properties of
ceramic and polymer [Furukawa 1976, Dias 1996, Sakamoto 2006, Wong 2006, Kumar 2005,
Estevam 2011, Feng 2010].
According to Newnham and co-workers [Newnham 1978] there are ten connectivity
patterns in which a two phase composite system can be fabricated, ranging from
unconnected 0-0 pattern to a 3-3 pattern in which both phases are three dimensionally self-
connected. The easier and cheaper composite to obtain is the 0-3 pattern, that means the
ceramic grains are dispersed (unconnected) into a polymer matrix (self-connected three
dimensionally). The main goal of embedding ferroelectric ceramic grains within a polymer
matrix is to obtain a material which displays the combined better properties of each single
phase. However it is very difficult to obtain a 0-3 composite with high ceramic content.
There are basically two problems: high ceramic content will provide a mixed connectivity
due to the percolation of the grains; high ceramic concentration means low flexibility of the
composite material.
But these problems have not drawn the interest of researchers in using the 0-3 composite, on
the contrary, it intensified the search for optimum results and many studies on the
polarization of the composites have been conducted [Furukawa 1986, Lau 2007, Ploss 2001,
Wong 2002]. Still seeking a more effective polarization of the composite material, studies
with the inclusion of a semiconductor phase were carried out [Sa-Gong 1986, Sakamoto

2002, Renxin 2006, Ploss 2006, Chau 2007]. These efforts were not in vain and 0-3 composites
are being used as sensors and transducers, and is now a well-established alternative to
conventional ferroelectric materials for many applications. New methods of preparing
ferroelectric ceramics have also been studied and the latest is the hydrothermal method for
obtaining ceramic powder [Shimomura 1991, Morita 2010]. The grain size and structure are
also objects of study.
This work presents the preparation and characterization of PZT ceramic obtained by
different methods. The influence of the synthesis method on the grain size and the
morphology are also object of study. The fabrication and characterization of composite
films with 0-3 connectivity, immersing nanoparticles of PZT into the non-polar
poly(vinylidene fluoride) – PVDF as the polymer matrix were presented. For comparison
there are some results obtained with composite samples made of ceramic particles
Lead Titanate-Based Nanocomposite:Fabrication,
Characterization and Application and Energy Conversion Evaluation

253
recovered with a conducting polymer and also using the conducting polymer as a third
phase. Moreover it presents the results obtained with the new material that includes a
semiconductor phase, polyaniline – PAni as a sensing material and as a piezoelectric
material for energy harvesting. In this sample the PZT grain was partially covered by
PAni, which allowed better distribution of grains in the polymer matrix in comparison
with the inclusion of the 3rd phase separately, avoiding a continuous electrical flux path
which does not allow the polarization process of the composite sample. The use of this
composite as sensor and power converter is an indicative that it is a good alternative for
technological applications.
2. Experimental
2.1 Ceramic
The control of some parameters is important to achieve the desired properties in lead
zirconate titanate (PZT) materials. These parameters include the absence of intermediate
crystalline phases, a defined and fixed stoichiometry, as well as a homogeneous distribution

of lead in the material. Lead zirconate titanate (PZT) is a very interesting ceramic that has
good piezoelectric properties used to making ultrasonic transducers, filters and pyroelectric
detectors [Haertling 1999]. This material can be prepared using different ways but the most
important is using low temperature to obtain the crystalline phase. This condition promotes
the homogeneous lead distribution and consequently occurs the formation of pure phase
PZT. The presence of secondary phases reduces the dielectric and piezoelectric constants
[Zaghete 1999, Zaghete 1992]. To minimize theses problems some chemicals processes has
been proposed as the optional procedure. Methods such as sol-gel [Ishikawa 1994],
hydrothermal synthesis [Pan 2007, Abothu 1999] and Pechini's method [Zaghete 1992] can
be used.
It is known that ceramic materials prepared from chemical solutions routes are
transformed via a nucleation and growth process, often requiring high temperatures to
surmount the large energy barriers of the nucleation and growth of the stable phase.
Consequently, these energy barriers frequently determine the calcinations conditions and
therefore the characteristics such as, particle size, morphology and degree of aggregation
of the precursor powder. The most significant advance in this field, however, consists of
the ability to control phase development at low calcinations temperatures to avoid lead
evaporation.
The expected phase equilibrium (perovskite) may grow starting from a gel matrix under a
nucleus along a certain crystallographic orientation. This type of heterogeneous nucleation
eliminates the need for the system to exceed the activation energy required to form the
nucleus, as in the case of systems with homogeneous nucleation. As a result, the perovskite
phase may crystallize at lower temperatures.
The present study show the influence of synthesis method on size and morphologic
distribution of particle and the amount of perovskits phase synthesized at different
temperatures. The procedure of PZT synthesis, based on Pechini’s method [Zaghete 1992]
makes use of the capability that certain α-hydroxycarboxylic organic acids possess of
forming polybasic acid chelates with several cations. When mixing with a polyhydroxylic
alcohol and heating, the chelate transforms into a polymer, maintaining the cations
homogeneously distributed.

Ferroelectrics – Material Aspects

254
The organic part is eliminated at low temperatures forming reactive oxides with well-
controlled stoichiometry. Pure PZT with composition Pb(Zr
0.48
Ti
0.52
)O
3
can be prepared from
the metal-citrate complex polyesterified in ethylene glycol. Appropriate quantities of Zr, Ti
and Pb solutions were mixed and homogenized by stirring at 90°C for 3 h. Next, the
temperature was increased to 130-140°C, yielding a high viscous polyester resin. The
powder was calcined at 600, 700 and 800C for 2h and ball milled for 2h in isopropylic
alcohol medium.
Recently, the hydrothermal synthesis has been widely used in the study of these materials
for the production of particles with nanometric sizes, high purity and crystallinity, good
stoichiometric control and good yield. There are few reports relating to the study on the
PZT synthesized by the hydrothermal method in literature. In one of these works, PZT
powder was obtained with cubic morphology and crystalline phase by hydrothermal
synthesis [PAN 2007]. By controlling the variables process of the synthesis, it becomes
possible to change the morphology, the particle size, as well as the hydrothermal
synthesis assisted by microwave method that has the advantage of producing rapid
heating, thereby promoting homogeneous nucleation of particles [Moreira 2009, Rao
1999].
Hydrothermal media provide an effective reaction environment for the synthesis of
numerous ceramic materials because of the combined effects of solvent, temperature, and
pressure on ionic reaction equilibrium. The conventional hydrothermal method has become

an effective synthetic route in Materials science by dramatically increasing the control of the
micro/nanometric morphology and orientation [LUO 2008]. In addition, this method is
environmentally friendly and depends on the solubility of the chemical salts in water under
temperature and pressure conditions.
The key factors in this method are the vapor pressure and solubility of the chemical
salts in water [Lencka 1995]. In contrast to the conventional hydrothermal method which
requires a long time typically several days and high electric power (over thousand
watts) [Dutta 1994], microwave-assisted heating is a greener approach to synthesize
materials within a shorter time typically several minutes to some few hours less than the
duration of the conventional method and with lower energy consumption (hundreds of
watts).
The desired PZT product can be synthesized using Pb(NO
3
)
2
, ZrOCl
2
.8H
2
O, TiO
2
, KOH . At
first, a suspension containing ZrOC
2
.8H
2
O, Pb(NO
3
)
2

and TiO
2
was prepared in aqueous
medium. After that, KOH aqueous solution containing 3.31g of KOH (1.84 mol.L
-1
, pH=14).
was add to the precursor suspension and then kept at room temperature under stirring for
approximately 20 minutes. It was further placed containing all the reagents in Teflon jars,
sealed and taken to the microwave for the synthesis of PZT powder.
The synthesis temperature was 180
o
C and the lower time used to obtain PZT was 0.5 hour,
under constant pressure of approximately 10 Bar. The PZT powders were synthesized using
microwave-assisted hydrothermal digester (MARS CEM, USA). The precursor was further
again loaded into a 90 mL Tefflon autoclave reaching 30% of its volume. The autoclave was
sealed and placed into a microwave-assisted hydrothermal system using 2.45 GHz
microwave radiation with a maximum output power of 800 W. Then the solid product was
washed with distilled water until a neutral pH was obtained and was further dried at room
temperature.
Lead Titanate-Based Nanocomposite:Fabrication,
Characterization and Application and Energy Conversion Evaluation

255
20 30 40 50 60 70 80

Pechini 800ºC
(001)/(100)
(110)
(111)
(002)

(200)
(102)
(200)
(112)
(211)
(022)
(221)
(301)
Intensity (a.u)
Pechini 700ºC

Pechini 600ºC
2


SHM 0.31mol.L
-1
180ºC/1h

Fig. 1. X-ray diffraction patterns for PZT powders synthesized by Pechini method at
different temperatures of calcination and hydrothermal synthesis assisted by microwaves.

0
20
40
60
80
100
0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0
Diameter, m

Porcentagem %
Pechini 600ºC
1,5m
0
20
40
60
80
100
0,51,01,52,02,53,03,54,04,55,05,56,06,57,0
Diameter,m
Percentage, %
Pechini 800ºC
1,5 m

0
20
40
60
80
100
0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0

Percentage, %
Pechini 700ºC
1,47m
Diameter,m
0
20
40

60
80
100
0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0
Percentage, %
SHM 0.31 mol.L
-1
2h
2,6m
Diameter,
m

Fig. 2. Diagrams of particles size distribution of PZT synthesized by the Pechini’s method
calcimine at (a) 600
o
C; (b) 700
o
C

; (c) 800
o
C and (d) synthesized by hydrothermal microwave
method at 180
o
C/1h.

Ferroelectrics – Material Aspects

256

(A) (B)

(C) (D)
Fig. 3. FEG-SEM images of PZT nanostructures synthesized by Pechini’s method: (a)
600
o
C/3h; (b) 700
o
C/3h, (c) 800
o
C/3h and (d) synthesized by hydrothermal microwave
method at 180
o
C/1h.
Lead Titanate-Based Nanocomposite:Fabrication,
Characterization and Application and Energy Conversion Evaluation

257
The obtained powders were characterized by X-ray powder diffraction using a Rigaku,
DMax 2500PC with rotator anode at 50 kV and 150 mA, Cu Kα radiation in the 2θ range
from 20° to 80° with 0.02°min
-1
. A field emission gun scanning electron microscope (SEM-
FEG)-ZEISS SUPRA 35 microscope was used to analyze the shape and size of particles;
energy dispersive X-ray microanalysis spectroscopy (EDS) was used for compositional
determination. All measurements were taken at room temperature.
Today it is well known the effectiveness of the synthesis rote on the perovskits phase
formation but it isn't well understood the influence of the particle size on the composite
properties. Some of results obtained for PZT prepared by pechini´s method and synthesis
hydrothermal assisted by microwave were presented to show the different characteristic as

function of the synthesis way.
The analysis of the crystal structure of the material indicated mixture of the tetragonal and
rhombohedral phase that is characteristics of the morphotropic phase transition region (YU
2007) Figure 1. When prepared by the Pechini’s method has been the formation of pure
crystalline phase from 600
o
C, the same result can be observed with hydrothermal treatment
at 180
o
C for 1 hour. Also is possible to observe that the distribution of particle size and
average particle size are directly affected by the temperature of thermal treatment as well as
by the synthesis process, Figures 2 and 3. The purity of the composition was analyzed by
EDS and found a homogeneous distribution of Pb, Ti, Zr on the surface of the entire sample
as showed in Figure 4.


(a)

(b)
Fig. 4. Energy dispersive scanning, EDS, results of PZT prepared by Pechini’s Method at (a)
700ºC/3h and (b) synthesized by the hydrothermal microwave method. At 180
o
C/1h.

Ferroelectrics – Material Aspects

258
2.2 Polymer matrix
Poly(vinylidene fluoride) (PVDF) is a thermoplastic with excellent mechanical, optical and
thermal properties, and showing resistance to attack of various chemicals [Lovinger 1982].

Formed by repeated units of (-H
2
C-CF
2
-)
n
, has a molecular weight around 105 g / mol.
Depending on the means of acquiring or thermal history, PVDF can possess the degree of
crystallinity from 45 to 60%, melting temperature (Tm) in the range from 165 to 179°C and
glass transition temperature (Tg) of about -34°C. Its crystal structure is spherulitic
(composed of lamellar crystalline radial). The range of relatively low melting temperature
and some properties of the polymer described above ensure easy processing by melting and
blending, which means great advantage in large scale production. The PVDF can also be
processed by casting that may result in thin films.
Relative to the molecular structure, PVDF is a linear polymer that has permanent electric
dipoles approximately perpendicular to the direction of their chains. These dipoles are
formed by the electronegativity difference between atoms of hydrogen and fluorine. PVDF
can be found in four distinct structural phases α, β, γ and δ.
α phase is the most common, this being non-polar usually obtained by cooling molten. The
β phase (polar) is very attractive technical-scientific because of its piezoelectric and
pyroelectric activity.
2.3 Getting PZT grains coated with PAni
The monomer aniline (C
6
H
5
NH
2
) was purchased from Sigma-Aldrich and used in the
synthesis after vacuum distillation. For the polymerization of aniline was employed oxidant

ammonium persulfate from MERCK. To obtain the PZT particles partially coated with
polyaniline, the PZT powder was incorporated into the solution of aniline and 1M cloridric
acid under stirring at a temperature around 2°C for approximately 2 h. The solution was
filtered and washed with 0.1M hydrochloric acid and the product was dried in an oven at
50°C for 3h.
Figure 5 shows the FEG-SEM micrograph of (a) the PZT and (b) PAni-coated PZT particles.
It can be seen the lack of smooth of the coated-particle surface.
2.4 Composite
The PVDF in the form of powder was mixed with pure PZT, the PZT particles coated with
PAni and PAni and PZT placed separately. The mixtures were then placed between sheets
of Kapton and pressed close to the melting temperature of PVDF. To find the optimum
condition for preparation of the composite film the effect of pressing temperature, time and
pressure to be taken by the mixtures were studied.The optimum conditions were found to
be: temperature of 185°C for about 1 minute at a pressure of about 7.6 MPa. The thickness of
the films was in the range from 100 to 420 m depending on the ceramic content. The
composite films were obtained with different volume fractions of ceramic, which was
calculated using the equation below [Marin-Franch 2002]:

1
pc
c
c
p
c
m
m







(1)
where m is the mass and  is the density. The subscript c and p are related to ceramic and
polymer, respectively. c is the volume fraction of ceramic. Figure 6 shows FEG images of
the composite sample. It can be seen the homogeneous distribution of the ceramic
nanoparticles recovered with PAni.