This article investigates the phase formation, morphology, and ferroelectric properties of NaNbO3–PbTiO3 (NN-PT) composite ceramics with the formula (1-x)NaNbO3-(x)PbTiO3, where x ranges from 0 to 1.0. The ceramics were prepared by a solid-state reaction method and analyzed using XRD, SEM, and dielectric and ferroelectric property measurements. The results showed that perovskite phases formed over the entire compositional range without unwanted phases. The addition of PbTiO3 significantly affected the microstructure and properties of the NaNbO3 ceramics, with maximum dielectric constant and remnant polarization observed at x=

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Investigations on Morphology
and Ferroelectric Properties of
NaNbO3–PbTiO3 Composite Ceramics
A. Prasatkhetragarn
a
, R. Saenarpa
a
, B. Yotburut
a
, P. Ketsuwan
a
,
T. Sareein
b
, S. Ananta
b
& R. Yimnirun
c
a
School of Science, University of Phayao, Phayao, 56000, Thailand
b
Department of Physics and Materials Science, Faculty of Science,
Chiang Mai University, Chiang Mai, 50200, Thailand
c
School of Physics, Institute of Science, Suranaree University of
Technology, Nakorn Ratchasima, 30000, Thailand
Available online: 27 Jun 2011
To cite this article: A. Prasatkhetragarn, R. Saenarpa, B. Yotburut, P. Ketsuwan, T. Sareein, S. Ananta
& R. Yimnirun (2011): Investigations on Morphology and Ferroelectric Properties of NaNbO3–PbTiO3
Composite Ceramics, Ferroelectrics, 416:1, 40-46
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2. Ferroelectrics, 416:40–46, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 0015-0193 print / 1563-5112 online
DOI: 10.1080/00150193.2011.577664
Investigations on Morphology and Ferroelectric
Properties of NaNbO3–PbTiO3 Composite Ceramics
A. PRASATKHETRAGARN,1,∗
R. SAENARPA,1
B. YOTBURUT,1
P. KETSUWAN,1
T. SAREEIN,2
S. ANANTA,2
AND R. YIMNIRUN3
1
School of Science, University of Phayao, Phayao 56000, Thailand
2
Department of Physics and Materials Science, Faculty of Science, Chiang Mai
University, Chiang Mai 50200, Thailand
3
School of Physics, Institute of Science, Suranaree University of Technology,
Nakorn Ratchasima 30000, Thailand
Ceramics in NN–PT system with a formula (1−x)NaNbO3–(x)PbTiO3 (where x = 0, 0.1,
0.2, . . . , 1.0) were prepared by a solid state mixed oxide technique. The phase formation
behavior and microstructure were studied using x-ray diffraction (XRD) and scanning
electron microscopy (SEM), respectively. The dielectric and ferroelectric properties of
the compounds were studied and discussed. Phase pure perovskites of NN–PT ceramics
were obtained over a wide compositional range. This work was then aimed to determine
the phase formation, morphology, dielectric and ferroelectric properties of NN–PT
ceramics. Interestingly, the results showed that the addition of PT have been strongly
affected on morphology and ferroelectric properties of NN ceramics.
Keywords NN–PT; Composite; Ferroelectric properties; Morphology; Phase
formation.
1. Introduction
Lead-based ferroelectric ceramics exhibit superior electrical and electromechanical prop-
erties at the morphotropic phase boundary (MPB) because of the large number of available
polarization directions [1]. Therefore, there have been many attempts to find new compo-
sitions in the vicinity of MPB not only with relatively high TC (Curie temperature) but also
with good electrical and electromechanical properties [1–2]. Lead titanate (PbTiO3 or PT)
is a ferroelectric, having a highly symmetric perovskite-type structure with a high curie
temperature (TC) of about 490◦
C at which the phase transition of tetragonal ferroelectric
phase to cubic paraelectric phase occurs [1–3]. The PT ceramic is a useful pyroelectric and
piezoelectric material for high-temperature or high-frequency applications, such as non-
volatile memories, infrared sensors and capacitors [4]. It is difficult to prepare a pure-phase
PT ceramics with high density, as a result of a high c/a ratio of about 1.06 which gives
rise to stresses in these ceramics, hence they can be easily broken and difficult to prepare
Received June 20, 2010; in final form July 18, 2010.
∗
Corresponding author. E-mail: Prasatkhetragarn@yahoo.com
[428]/40
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3. Properties of NaNbO3–PbTiO3 Composite Ceramics [429]/41
in shape and size suitable for device applications. The most widely used approach is the
formation of solid solution by adding additives, such as rare earth elements, alkaline earth
elements and another compounds, this is the promising technique for producing crack-free
high-density materials [5–6]. However, the properties of PT itself are subsequently altered
by the additives and as it has been known that PT has a good electrothermal property so the
stoichiometric PbTiO3 is still needed.
Sodium niobate NaNbO3 has claimed the attention of researchers and designers of
equipment owing to its unique physical properties and as a basis for a class of ecolog-
ically benign active materials [7]. An intriguing feature of NaNbO3 is that it shows the
largest—among the oxygen octahedral perovskites—number of structural phase transitions
between nonferroelectric (NFE), antiferroelectric (AFE) and ferroelectric (FE) phases. The
presence of six phase transitions in the temperature range from T = 650◦
C to T = −120◦
C
is generally accepted [7–8]. As well known, NaNbO3 generally exhibits antiferroelectric
properties at room temperature with orthorhombic structure and space group Pbma. At high
temperatures NaNbO3 has cubic perovskite structure with space group Pm3m [7–8].
On the basis of the above mentioned approach, solid solutions of NN and PT are
expected to synergistically combine the properties of both the normal ferroelectric PT and
antiferroelectric NN, which could exhibit electrical properties that are better than those of
the single-phase of NN and PT. Therefore, the overall purpose of this study is to determine
the phase formation, microstructure, dielectric and ferroelectric properties of ceramics in
a (1−x)NaNbO3–(x)PbTiO3 (where x = 0, 0.1, 0.2, . . . , 1.0) system prepared with the
simple solid state mixed oxide technique.
2. Experimental Procedure
Raw materials of lead oxide, PbO (Fluka, >99% purity), titanium oxide, TiO2 (anatase-
structure) (Fluka, >99% purity), sodium carbonate, Na2CO3 (Sigma-Aldrich, 99.0% pu-
rity), Nb2O5 (Sigma-Aldrich, 99.9% purity) were used into batch calculation and prepara-
tion. In the present work, the (1−x)NaNbO3–(x)PbTiO3, where x = 0, 0.1, 0.2, . . . , 1.0,
compositions were prepared and synthesized by the solid-state reaction of these raw mate-
rials and mixed by ball-milling technique in ethanol for 24 h. After drying, the product was
calcined in an alumina crucible at a temperature of 900◦
C for 5 h with a heating/cooling rate
5◦
C/min. The calcined powders were uniaxially cold-pressed at 1500 psi into disc-shaped
pellets with a diameter of 10 mm and a thickness of 1 mm, with 3 wt% poly (vinyl alcohol)
(PVA) added as a binder. Following binder burnout at 500◦
C, the pellets were sintered at
1200◦
C for 2 h at a heating/cooling rate of 5◦
C/min.
The phase structure of the ceramics was analyzed via X-ray diffraction (XRD; Bruker-
AXS D8). The microstructures of the surface sintered pellets were examined using scanning
electron microscopy (SEM; JEOL JSM-840A). The dielectric properties of the samples were
measured using an automated measurement system. An Agilent 4284A LCR meter was
used to measure the room temperature dielectric properties over a wide composition. The
room temperature ferroelectric properties were examined using a simple Sawyer–Tower
circuit at fixed measuring frequency of 50 Hz.
3. Results and Discussion
The XRD patterns of (1−x)NaNbO3 – (x)PbTiO3 ceramics with various x values from x =
0, 0.1, 0.2, . . . , 1.0 are shown in Fig. 1. It can be seen that a complete crystalline solution
of the perovskite structure is formed throughout the entire compositional range without
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Figure 1. XRD patterns of PZT and 0.9PZT-0.1PFN ceramics.
Figure 2. c/a ratios of NN-PT ceramics.
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5. Properties of NaNbO3–PbTiO3 Composite Ceramics [431]/43
the presence of pyrochlore or unwanted phases. From the XRD patterns, NaNbO3 ceramic
is identified as a single-phase material with a perovskite structure having orthorhombic
symmetry which could be matched with JCPDS file no. 33–1270. The XRD patterns of
the NN–PT compositions show a combination between NN and PT patterns, showing a
perovskite structure having the symmetry varying between orthorhombic and tetragonal
types, similar behavior is also reported [9–12]. For better comparison, the JCPDS file no.
78–0298 for PbTiO3 with a tetragonal structural symmetry is also displayed in Fig. 1. As
well known, c/a ratios revealed the tetragonal symmetry which shows in the (100) and
(200) peaks splitting for the NN–PT system. It is clearly that tetragonal-rich phase with
increasing PT content, as shown in Fig. 2. This trend is similar to those reported in the
literature [9, 12].
The SEM images in Fig. 3 reveal that the addition of PbTiO3 results significant changes
in the microstructure of the NaNbO3 ceramics. The pure NN ceramic shows irregular
Figure 3. SEM micrographs of NN-PT ceramics.
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shape including small and large grain size, while PT shows polygon-shape. However,
the composite of NN-PT ceramics exhibited a quadrilateral shape with increasing PT
content up to x = 0.6, while ceramics close packing and density also increased, which
reaches maximum in this condition (density = 8.01 g/cm3
, while NN and PT have density
about 4.34 and 7.91, respectively). After that the grain shape significant changes to square
shape at compositions x = 0.7 to 0.9, which lower density than the composition x = 0.6.
Interestingly, the density results can be correlated to the microstructure because high-density
0.4NN−0.6PT ceramics show high degrees of grain close packing. A similar behavior has
also been observed [12].
Room temperature of the dielectric constant (εr) of the (1−x)NN−(x)PT ceramics
with various x values are shown in Fig. 4. The result shows maximum dielectric constant at
composition x = 0.6, the results can be correlated to the microstructure. However, the low
compounds of PT (x = 0 to 0.4) the results show NN-like behavior, while high PT content
exhibit PT-like behavior (x = 0.8 to 1.0). Moreover, the mixed NN and PT at composition
of 0.4NN-0.6PT clearly indicated that the stoishiometric was observed. An anomaly of
electrical properties at the MPB has also been observed in solid solutions of PZT-PNN,
PZT-PZN, and PZT-PMN [13–15].
The polarization-electric field (P–E) hysteresis loops of (1−x)NaNbO3–(x)PbTiO3
(where x = 0, 0.1, 0.2, . . . , 1.0) ceramics measured at 2.5 kV/cm are presented in Figs.
5. The remnant polarization of (1−x)NaNbO3–(x)PbTiO3 increased with increasing PT
content up to x = 0.6 and then decreased. In addition, the largest remnant polarization at x
= 0.6 could be caused by effects of morphology and density, which reaches maximum in
this condition. Moreover, the P–E hysteresis loops of pure NN and PT are not suitable clear
due to NaNbO3 generally exhibits antiferroelectric properties (could be exhibited double
loop, but nevertheless the low electric field of 2.5 kV can only present line or slim loop),
while PbTiO3 have low density and could not well exhibited hysteresis loop. Interestingly,
the mixing of NN and PT is suitable increases the ferroelectric properties better than those
compositions of NN and PT. Similar behavior is also reported [9–15].
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Figure 4. Room temperature on dielectric constants of 0 NN-PT ceramics.
Figure 5. Ferroelectric properties of NN-PT ceramics.
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4. Conclusion
In the present work, the pure-phase perovskite of (1−x)NaNbO3–(x)PbTiO3, where x
= 0, 0.1, 0.2, . . . , 1.0, ceramics were synthesized using a simple solid-state mixed-
oxide technique. Phase pure of NN and PT ceramics were identified by XRD as a single-
phase material with a perovskite structure having orthorhombic and tetragonal symmetry,
respectively, while the mixed compositions of NN-PT showed a gradual change from
orthorhombic to tetragonal with increasing PT content. The SEM images reveal that the
addition of PbTiO3 results strongly significant changes in the microstructure of the NaNbO3
ceramics. In addition, dielectric and ferroelectric properties of NN–PT ceramics were found
to enhance at the ceramic composition with x = 0.6. Most importantly, this study shows that
the addition of PT could improve the dielectric and ferroelectric properties in NN ceramics.
Acknowledgments
This work was supported by the Office of Higher Education Commission, the Thailand
Research Fund (TRF), National Metal and Materials Technology Center (MTEC), School
of Science and University of Phayao.
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