Structure and Electrical Properties of Oxide Doped Rhombohedral Pb(Ni1/3Nb2/3)O3-PbTiO3 Ferroelectric Ceramics

doi:10.4236/msa.2010.12012

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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.

Email: [email protected]

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





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



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

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

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

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

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

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

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)

(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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