Materials Sciences and Applicatio ns, 2010, 1, 66-71
doi:10.4236/msa.2010.12012 Published Online June 2010 (http://www.SciRP.org/journal/msa)
Structure and Electrical Properties of Oxide Doped
Rhombohedral Pb(Ni1/3Nb2/3)O3-PbTiO3
Ferroelectric Ceramics
Bijun Fang, Dun Wu, Qingbo Du, Limin Zhou, Yongyong Yan
School of Materials Science and Engineering, Changzhou University, Changzhou, China.
Received February 28th, 2010; revised May 3rd, 2010; accepted May 5th, 2010.
ABSTRACT
0.7Pb(Ni1/3Nb2/3)O3-0.3PbTiO3 (0.7PNN-0.3PT) and 1 mol% La2O3-, Y2O3-, ZnO-, MnO2- and Nb2O5-doped 0.7PNN-
0.3PT ferroelectric ceramics were prepared by the conventional solid-state reaction method via the columbite precursor
route. The ceramics sintered at 1180 ℃ exhibit pure rhombohedral perovskite structure except the Y2O3-doped
0.7PNN-0.3PT ceramics. The oxide-doped 0.7PNN-0.3PT ceramics exhibit rather homogeneous microstructure and
improved densification, especially for the MnO 2-and La2O3-doped 0.7PNN-0.3PT (defect) ceramics whose relative
density is larger than 96%. All the above dopants decrease the dielectric loss of the 0.7PNN-0.3PT ceramics, whereas the
values of the dielectric maximum (

m) and the temperature of

m (Tm), and the character of dielectric response vary
differently. ZnO and Nb2O5 doping increase remanent polarization Pr, and La2O3, ZnO, MnO2 and Nb2O5 doping
decrease coercive field Ec of the 0.7PNN-0.3PT ceramics. Piezoelectric property is greatly improved by Y2O3, MnO2,
Nb2O5 and ZnO doping, where the MnO2-doped 0.7PNN-0.3PT ceramics exhibit the largest value of piezoelectric
constant d33, which reaches 191 pC/N.
Keywords: Lead Nickel Niobate-Lead Titanate, Perovskite, Dielectric Property, Ferroelectric Property, Piezoelectricity
Property
1. Introduction
Relaxor-based ferroelectric ceramics have arisen exten-
sive research due to their high and nearly temperature
insensitive dielectric constant, electromechanical constant
and electro-optical performance, which make them po-
tential revolution in electromechanical transducer and
actuator applications and promising candidates for optical
devices [1,2]. To meet the requirements of these applica-
tions, ideal materials should possess high relative dielec-
tric constant and low dielectric loss. Recently, a novel me-
thodology is devised to stabilize perovskite phase and
develop piezoelectric materials by adding stable perovs-
kite normal ferroelectrics to relaxor ferroelectrics. The
formation of solid solutions increases the tolerance factor
and electronegativity difference, leading to the stabiliza-
tion of the perovskite structure [3,4].
Among relaxor ferroelectrics, Pb(Ni1/3Nb2/3)O3 (PNN)
is a typical relaxor ferroelectric with perovskite structure,
which exhibits broad and diffused dielectric response
peaks accompanied by apparent dielectric frequency dis-
persion. PbTiO3 (PT) is a typical normal ferroelectric
sharing perovskite structure, which exhibits sharp and
frequency independent dielectric response peaks at Curie
temperature (TC) 490℃. Since the arrangement of het-
erovalent cations in the perovskite structure, their elec-
trostatic interactions and the morphotropic phase bound-
ary (MPB) effects affect electrical properties of ferro-
electrics greatly, the development of perovskite structure
and the MPB composition of the solid solution (1-x)-
Pb(Ni1/3Nb2/3)O3-xPbTiO3 (PNN-PT) have arisen great
research attention [5,6].
In this paper 0.7Pb(Ni1/3Nb2/3)O3-0.3PbTiO3 (0.7PNN-
0.3PT) ferroelectric ceramics were prepared by the co-
lumbite precursor method. This composition was chosen
since 0.7PNN-0.3PT locates around the MPB composition
and exhibits typical rhombohedral structure, which re-
veals enhanced microstructure and electrical properties,
and was easy to research the effects of che- mical doping
on structure and performance of the ferroelectric solid
solution. La2O3, Y2O3, ZnO, MnO2 and Nb2 O5 were used
as dopants to investigate the influence on stabilization of

Structure and Electrical Properties of Oxide Doped Rhombohedral Pb(NiNb )O -PbTiO Ferroelectric Ceramics 67
1/32/3 3 3
00/
the perovskite structure, electrical properties and MPB
effects of the PNN-PT system. By the way, special efforts
should be undertaken on ceramic processing and sintering
profile for the preparation of the lead-containing ferro-
electric ceramics in order to suppress the evaporation of
lead during sintering [7].
2. Experimental Procedure
0.7PNN-0.3PT and 1 mol% La2O3-, Y2O3-, ZnO-, MnO2-
and Nb2O5-doped 0.7PNN-0.3PT ferroelectric ceramics
were prepared by the conventional solid-state reaction
method via the columbite precursor route. The chemical
compositions were designed as below:
To maintain stoichiometry, the analytical-purity raw
oxides were dried separately before weighing and the
synthesized columbite precursors were weighed and in-
troduced into the batch calculation. The columbite pre-
cursors, NiNb2O6, ZnNb2O6 and MnNb2O6, were synthe-
sized by calcining of a mixture of stoichiometric NiO,
ZnO and MnO2 with Nb2O5, respectively, at 1000℃ for 4
h. Stoichiometric PbO, TiO2 and chemical dopants (zinc
and manganese were introduced in the form of ZnNb2O6
and MnNb2O6 columbite precursors) were added to
NiNb2O6, and the well-mixed powders were calcined at
900℃ for 2 h. The calcined powders were then dry-
pressed into pellets with the addition of 1 wt% polyvinyl
alcohol (PVA) binder and sintered at different tempera-
tures. Detailed preparation of the ceramics was described
elsewhere [8].
The sintered ceramics were ground and polished to
obtain flat and parallel surfaces. For electrical property
measurement, silver paste was coated on both surfaces of
the well-polished pellets and fired at 550℃ for 30 min to
provide robust electrodes. Detailed phase structure char-
acterization, micromorphology observation and electrical
properties measurement procedures were described else-
where [7-8].
3. Results and Discussion
For the preparation of lead-containing PNN-PT ferro-
electric ceramics, special attention should be paid for the
control of the evaporation of lead during sintering, which
helps to determine the appropriate sintering conditions
combined with the collective assessments of fabrication
cost and electrical properties. The 0.7PNN-0.3PT and
1mol% oxide-doped 0.7PNN-0.3PT ceramics were sin-
tered at 1100-1220℃. The columbite precursor method
exhibits superiority and feasibility in synthesizing com-
plex relaxor-based ferroelectric ceramics since the weight
loss during sintering is relatively low and phase-pure
perovskite structure can be obtained. Based on the results
of preliminary experiments, the appropriate sintering
condition for 0.7PNN-0.3PT is 1180℃ for 2 h.
XRD patterns of the 0.7PNN-0.3PT and 1 mol% ox-
ide-doped 0.7PNN-0.3PT ceramics sintered at the opti-
mized conditions are shown in Figure 1. All the sintered
ceramics exhibit pure rhombohedral perovskite structure
except for Y2O3-doped 0.7PNN-0.3PT, where slight con-
tent of Pb3Nb4O13-type pyrochlore phase appears. The
appearance of pyrochlore phase can be attributed to the
ionic radius difference between Pb2+ and Y3+, and the
evaporation of lead during sintering and the deterioration
of the stabilization of perovskite structure induced by
Y2O3 doping. The content of pyrochlore phase of the
Y2O3-doped 0.7PNN-0.3PT ceramics can be determined
by an approximate method
%1
pyro
pyrochlore I


p
erov Pyro
II, where Iperov and Ipyro are the relative in-
tensity of the (110) perovskite diffraction peak and the
(222) pyrochlore diffraction peak, respectively, being
4.59%.
Cell parameters and density of the pure and oxide-
doped 0.7PNN-0.3PT ceramics are shown in Table 1
based on XRD results and density measurement by Ar-
chimedes water-immersed method. Since pure rhombo-
hedral perovskite structure forms in the oxide-doped
0.7PNN-0.3PT ceramics except Y2O3-doped one, the do-
ped cations tend to occupy A- or B-site of the perovskite
structure. However, due to the difference of the ionic
radius between the doping and the replaced cations, the
perovskite structure distorts, leading to the variation of
cell parameters and cell volume of the perovskite structure.
The relative density of 0.7PNN-0.3PT is not high enough
at this experimental conditions, which confirms again the
difficulty of the preparation of complex perovskite ferro-
electric ceramics [9]. Therefore, the ceramic processing
1/32/3 33
0.990.011/32/3 0.7(0.3-0.01/4)323
0.990.011/32/3 0.70.3323
0.7Pb(NiNb)O-0.3PbTiOabbr. as: 0.7PNN-0.3PT
(PbLa)(NiNb)TiOabbr. as: LaO-doped 0.7PNN-0.3PT
(PbLa)(NiNb)TiOabbr. as: LaO-doped 0.7PNN-0.3PT

0.990.011/32/3 0.7(0.3-0.01/4)323
0.990.01 1/32/333
0.990.011/32/333
defect
(PbY)(NiNb)TiOabbr. as: Y O-doped 0.7PNN-0.3PT
0.7Pb[(NiZn)Nb]O-0.3PbTiOabbr. as: ZnO-doped 0.7PNN-0.3PT
0.7Pb[(NiMn)Nb]O-0.3PbTiOab2
1/32/330.990.0132 5
b
r. as: MnO-doped 0.7PNN-0.3PT
0.7Pb(NiNb)O-0.3Pb(TiNb)Oabbr. as: NbO-doped 0.7PNN-0.3PT

68 Structure and Electrical Properties of Oxide Doped Rhombohedral Pb(NiNb )O -PbTiO Ferroelectric Ceramics
1/32/3 3 3
10 20 30 40 50 60 70 80
0
3000
6000
9000
12000
15000
18000
21000
Nb2O5-doped0.7PNN-0.3PT
MnO2-doped0.7PNN-0.3PT
ZnO-doped 0.7P N N-0.3PT
Y2O3-doped 0.7PNN-0.3PT
La2O3-doped 0 .7P NN -0.3PT (defect)
La2O3-doped 0 .7P NN -0.3PT
0.7PNN- 0. 3PT
(222)
(310)
(300)
(22 0 )
(211)
(21 0 )
(200)
(11 1 )
(110)
(100)
*
* py r ochl ore phase
Intensity ( a.u. )
2 ( o )
Figure 1. XRD patterns of the pure and oxide-doped 0.7PNN-0.3PT ceramics sintered at 1180 C for 2 h
Table 1. Cell parameters and density of the pure and oxide-doped 0.7PNN-0.3PT ceramics
Composition a = b = c
(Å)  =  =  ()Cell volume (Å3)
Theoretical density
(g/cm3)
Bulk density
(g/cm3)
Relative density
(%)
0.7PNN-0.3PT 4.0039(8) 90.012(81) 64.187 8.4497 7.520 88.99
La2O3-doped 0.7PNN-0.3PT 4.0057(9) 90.037(137)64.271 8.4179 7.398 87.88
La2O3-doped 0.7PNN-0.3PT
(defect) 4.0028(13) 89.991(137)64.135 8.4389 8.424 99.82
Y2O3-doped 0.7PNN-0.3PT ~4.0082(16) ~90.022(165)~64.395 ~8.3888 7.073 ~84.31
ZnO-doped 0.7PNN-0.3PT 4.0054(41) 90.091(428)64.256 8.4410 7.692 91.13
MnO2-doped 0.7PNN-0.3PT 4.0035(27) 90.064(280)64.166 8.4522 8.140 96.31
Nb2O5-doped 0.7PNN-0.3PT 4.0039(26) 90.070(265)64.187 8.4532 7.347 86.91
should be tailored further. Small content of oxide doping
exhibits great effect on the densification of the 0.7PNN-
0.3PT ceramics. Among which, the MnO2- and La2O3-
doped 0.7PNN-0.3PT (defect) ceramics exhibit the largest
relative density, being more than 96% of the theoretical
density, which is especially suitable for the electronic
industry applications. Above results indicate that chemi-
cal doping is an efficient way to improve densification of
ferroelectric ceramics.
The improved densification of the sintered MnO2- and
La2O3-doped 0.7PNN-0.3PT (defect) ceramics is further
confirmed by SEM observation, which is shown in Figure
2. The both oxide-doped 0.7PNN-0.3PT ceramics exhibit
rather homogeneous microstructure morphology, where
almost no gas pores exist and exaggerated growth of ab-
normal grains are few. Such results conform well to the
density measurement, where the bulk density of the
MnO2- and La2O3-doped 0.7PNN-0.3PT (defect) ceramics
is 8.140 and 8.424g/cm3, which reaches 96.31% and
99.82% of the theoretical density, respectively. Liq-
uid-phase sintering mechanism inevitably takes partial
effect in the densification of the oxide-doped lead-con-
taining ferroelectric ceramics since most grains exhibit
round morphology [10].
Temperature dependence of dielectric constant of the
pure and oxide-doped 0.7PNN-0.3PT ceramics is shown
in Figure 3. The dielectric anomalies appeared at different
temperatures are generally ascribed to the ferroelectric
phase transition (FPT) from rhombohedral ferroelectric
phase to cubic paraelectric phase with the increase of
temperature [11]. Due to the oxide doping, the tempera-
ture of dielectric maximum (Tm) varies accompanied by

Structure and Electrical Properties of Oxide Doped Rhombohedral Pb(NiNb )O -PbTiO Ferroelectric Ceramics 69
1/32/3 3 3
Figure 2. SEM images of free surface of the MnO2- (a) and
La2O3-doped 0.7PNN-0.3PT (defect) (b) ceram ics sintered at
1180℃ for 2 h after thermal etching at 825℃ for 30 min
20 40 60 80100120140
0
5000
10000
15000
20000 0.7PNN-0.3PT
La2O3-doped 0.7PNN-0.3PT
Y2O3-doped 0.7PNN-0.3PT
ZnO-doped 0.7PNN-0.3PT
MnO2-doped 0.7PNN-0.3PT
Nb2O5-doped 0.7PNN-0.3PT
Dielectric constant
Tem perature ( oC )
Figure 3. Temperature dependence of dielectric constant of
the pure and oxide-doped 0.7PNN-0.3PT ceramics meas ured
at 0.5 kHz upon heating
20 40 60 80100120140
3000
6000
9000
12000
15000
18000
21000
0.7PNN-0.3PT
Dielectric constant
0.5kHz
1kHz
10kz
50kHz
100kHz
20 40 60 80100120140
3000
6000
9000
12000
15000
18000
21000
MnO2-doped 0.7PNN-0.3PT
ZnO-doped 0.7PNN-0.3PT
Dielectric constant
Temperature ( oC )
Figure 4. Temperature dependence of dielectric constant of
the pure, ZnO- and MnO2-doped 0.7PNN-0.3PT ceramics
measured at several fre quencies upon heating
the variation of the value of dielectric constant maximum
(m). The variation of the values of Tm and m can be at-
tributed to the distortion of the perovskite structure, which
is induced by oxide doping.
Detailed dielectric properties are shown in Figure 4
using the pure, ZnO- and MnO2-doped 0.7PNN-0.3PT
ceramics as examples. The dielectric response peaks of
-15 -10-5051015
-30
-20
-10
0
10
20
30
La2O3-doped 0.7PNN-0.3PT (defect)
0.7PNN-0.3PT
La2O3-doped 0.7PNN-0.3PT
Polariza tion ( C/cm2 )
Electric field ( kV/cm )
-15 -10-5051015
-30
-20
-10
0
10
20
30 Y2O3-doped 0.7PNN-0.3PT
ZnO-doped 0.7P NN-0.3PT
Polarization ( C/cm2 )
Electric field ( kV/cm )
-15 -10-5051015
-30
-20
-10
0
10
20
30 MnO2-doped 0.7PNN-0.3PT
Nb2O5-doped 0.7PNN-0.3PT
Pola r iza tion ( C/cm2 )
Electric field ( k V/cm )
Figure 5. P-E dielectric hysteresis loops of the pure and
doped 0.7PNN-0.3PT ceramics measured at room tempera-
ture
the both oxide-doped 0.7PNN-0.3PT ceramics are broa-
dened. However, the dielectric peaks of the ZnO-doped
0.7PNN-0.3PT ceramics exhibit more diffused and much
apparent dielectric frequency dispersion character as co-
mpared to that of the pure 0.7PNN-0.3PT ceramics. The
enhanced diffused phase transition occurs mainly due to
compositional fluctuation and/or substitutional disorder in
the arrangement of the B sites of the perovskite structure
induced by oxide doping. As a comparison, the dielectric
peaks of the MnO2-doped 0.7PNN-0.3PT ceramics are

70 Structure and Electrical Properties of Oxide Doped Rhombohedral Pb(NiNb )O -PbTiO Ferroelectric Ceramics
1/32/3 3 3
just broadened, whereas the frequency dispersion of the
dielectric behavior becomes almost vanish. The additional
dielectric anomalies appearing at elevated temperature
cannot be interpreted now, which maybe correlate with
relaxation polarization or thermal activated conduction
mechanism.
P-E dielectric hysteresis loops of the pure and oxide-
doped 0.7PNN-0.3PT ceramics are shown in Figure 5. All
the ceramics exhibit symmetric and fully saturated P-E
loops, where no apparent evidence of pinning effect is
observed [12]. The narrow character of the hysteresis
loops accompanied by small value of coercive field (Ec) is
characteristic of rhombohedral ferroelectrics. From the
fully saturated hysteresis loops, the values of the satura-
tion polarization (Ps), remanent polarization (Pr) and Ec
can be determined, which is shown in Table 2. The values
of Ps, Pr and Ec varies slightly due to the oxide doping. Ec
of the La2O3-doped 0.7PNN-0.3PT (defect) ceramics is
the smallest, being 1.23 kV/cm and Pr of the Nb2O5-doped
0.7PNN-0.3PT ceramics is the largest, being 8.96 C/cm2.
Therefore, ferroelectric properties of 0.7PNN-0.3PT can
be tailored by oxide doping.
Polarization conditions and piezoelectric property of
the pure and oxide-doped 0.7PNN-0.3PT ceramics are
shown in Table 3. Y2O3, ZnO, MnO2 and Nb2O5 doping
increases piezoelectric constant d33 of the 0.7PNN-0.3PT
ceramics, among which the MnO2-doped 0.7PNN-0.3PT
ceramics exhibit the largest value of d33, being 191 pC/N,
as compared to 65 pC/N of the pure 0.7PNN-0.3PT ce-
ramics. Therefore, dopant doping can improve piezoelec-
tric property of the 0.7PNN-0.3PT ceramics, which can be
attributed to the variation of composition, microstructure,
domain and crystal defect configuration.
4. Conclusions
0.7PNN-0.3PT and 1 mol% oxide-doped 0.7PNN-0.3PT
ferroelectric ceramics were prepared by the conventional
Table 2. Ferroelectric properties of the pure and oxide-
doped 0.7PNN-0.3PT ceramics measured at room tempera-
ture
Composition Ps
(μC/cm2)
Pr
(μC/cm2)
Ec
(kV/cm)
0.7PNN-0.3PT 23.2 6.33 1.58
La2O3-doped
0.7PNN-0.3PT 20.9 4.70 1.68
La2O3-doped
0.7PNN-0.3PT (defect) 19.7 2.17 1.23
Y2O3-doped
0.7PNN-0.3PT 22.4 5.57 1.24
ZnO-doped
0.7PNN-0.3PT 22.5 6.40 1.66
MnO2-doped
0.7PNN-0.3PT 23.1 6.19 1.64
Nb2O5-doped
0.7PNN-0.3PT 21.7 8.96 2.84
Table 3. Polarization conditions and piezoelectric property
of the pure and oxide-doped 0.7PNN-0.3PT ceramics
Composition
Polarization
electric field
(kV/mm)
Leakage current
(mA)
d33
(mean
value,
pC/N)
0.7PNN-0.3PT 2.83 0.003 65
La2O3-doped
0.7PNN-0.3PT 3.03 0.001-0.002 21
La2O3-doped
0.7PNN-0.3PT
(defect)
4.33 0.003 44
Y2O3-doped
0.7PNN-0.3PT 3.14 0.002 79
ZnO-doped
0.7PNN-0.3PT 4.20 0.001 87
MnO2-doped
0.7PNN-0.3PT 3.29 0.001-0.002 191
Nb2O5-doped
0.7PNN-0.3PT 2.08 0.003 89
ceramic processing via the columbite precursor method.
Phase pure rhombohedral perovskite structure can be obt-
ained for the ceramics sintered at 1180C except the
Y2O3-doped 0.7PNN-0.3PT ceramics. The oxide-doped
0.7PNN-0.3PT ceramics exhibit rather homogeneous
microstructure and improved densification, where the
relative density of the MnO2- and La2O3-doped 0.7PNN-
0.3PT (defect) ceramics reaches 96.31% and 99.82% of
the theoretical density, respectively. Oxide doping de-
creases dielectric loss of the 0.7PNN-0.3PT ceramics
accompanied by the variation of the value of dielectric
constant and Tm, and the character of dielectric frequency
dispersion. Ferroelectric and piezoelectric properties of
the 0.7PNN-0.3PT ceramics can also be tailored by oxide
doping.
5. Acknowledgements
The authors thank the International Scientific Cooperation
Project of Changzhou Scientific Bureau (Grant No. CZ
2008014) and the Natural Science Fundamental Research
Project of Jiangsu Colleges and Universities (Grant No.
08KJB430001) for financial support.
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