The Structure and the Electrical Properties of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 Ferroelectric Ceramics

doi:10.4236/msa.2011.29162

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Materials Sciences and Applications, 2011, 2, 1199-1204

doi:10.4236/msa.2011.29162 Published Online September 2011 (http://www.SciRP.org/journal/msa)

1199

The Structure and the Electrical Properties of

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3

Ferroelectric Ceramics

Malika Abba1, Ahmed Boutarfaia1,2*

1Laboratoire de Chimie Appliquée, Université de Biskra, RP-Biskra, Algérie; 2Département de Sciences de la Matière, Université de

Ouargla, RP-Ouargla, Algérie.

Email: *[email protected]

Received January 30th, 2011; revised March 9th, 2011; accepted May 31st, 2011.

ABSTRACT

The structural, the dielectric, and the piezoelectric properties of new ferroelectric

Pb0.95La0.05[Zrx,Ti(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 (0.46  x  0.55) ceramics have been investigated. All the samples were

being sintered at a temperature ranging from 1000 to 1180˚C after being compacted in circular discs. The detailed

structural and ferroelectric properties were carried out for sintered specimens. The results of X-ray diffraction showed

that all the ceramics specimens have a perovskite phase. The phase structure of

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3, In2/3)0.05]0.9875O3 ceramics was transformed from the tetragonal to the rhombohedral, with

an increase in the ratio of Zr/Ti in system. In the present system the MPB that coexists with the tetragonal and rhombo-

hedral phases is a narrow composition region of x = 0.50 – 0.51. The scanning Electron Microscopy (SEM) showed an

increase of the mean grain size when the sintering temperature was increased. The dielectric constant



and the cou-

pling factor Kp reached the maximum values, while the mechanical quality factor Qm and the loss tangent reached the

lowest values when x = 0.50. For the composition where x = 0.50, these properties include



= 5414 (at the Curie tem-

perature), tang



= 0.039, Kp = 0.67, Qm = 20 and a Curie temperature of 335˚C.

Keywords: MPB, Sintering, Piezoelectric, Dielectric, Zr/Ti Ratio, Ceramic

1. Introduction

The lead zirconate titanate materials Pb(ZrxTi1−x)O3 (PZT)

of a perovskite-type represented by the formula ABO3,

have been extensively used for the piezoelectric applica-

tions such as capacitors, sensors, actuators and other high

piezoelectric devices. In the PZT materials, the dielectric,

the ferroelectric, and the electromechanical characteris-

tics have been modified when several substitutions were

being done on the A- or/and B-sites, and also by varying

the ratio of Zr/Ti [1-6]. Since the discovery of the

behavior of the relaxor in Pb(Mg1/3,Nb2/3)O3 [7],

Pb(Zn1/3,Nb2/3)O3 [8], and Pb(Ni1/3,Nb2/3)O3 [9], the

studies of the ferroelectrics of the relaxor with Pb(B’1/3,

B”2/3)O3–type perovskites have attracted much attention

because of their excellent dielectric and electromechanical

properties. In a conventionally prepared PZT ceramics

with compositions near the morpho-tropic phase bound-

ary (MPB), the tetragonal, and the rhombohedral phases

always coexist [9]. The width and the properties of the

coexistence region are associated with the occurrence of

the compositional fluctuation of Ti4+ and Zr4+ ions in the

PZT materials [10]. The compositional fluctuation,

which is due to a non-uniform distribution of Titanium

and Zirconium ions, leads to a broad variation in the di-

electric constant accompanied with a Zirconium concen-

tration in the MPB region [11]. The width of this

coexistence region and the structure of the PZT ceramics

were greatly affected by the firing time and temperature

[12]. The selection of dopants or substitutions to tailor

some physical properties of PZT was based on many

factors which are the following: 1) charge neutrality, 2)

tolerance factors, 3) ionic radius, and 4) solubility/

miscibility. The substitution of lanthanides and the

different doped material at Pb-sites and Zirconium at the

Ti-sites with a different ratio of Zr/Ti have produced

many solid solutions with interesting properties for wide

industrial applications. The understanding of the relation-

ships between the variations in the physical properties

The Structure and the Electrical Properties of PbLa [Zr Ti (Mo ,In )]O Ferroelectric Ceramics

1200 0.95 0.05x(0.95–x)1/32/3 0.050.98753

and the phase coexistence with a composition is very

important because, first, they produce a great influence

on the characteristics of the PZT ceramics; and, second,

they stabilize the temperature and the time in the region

of the phase transition between the tetragonal and the

rhombohedral phases.

In this study,

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 piezoelec-

tric ceramics were investigated near the MPB by varying

the ratio of Zr/Ti. The purpose of this work was to study

the phase structure, the dielectric, and the piezoelectric

properties of these ceramics near the MPB in detail.

2. Experimental Procedure

The polycrystalline samples with a general composi-

tional formula Pb1–zLaz[ZrxTiy(Mo1/3,In2/3)1–(x+y)]1–z/4O3

with z = 0.05, (x + y)= 0.95 and 0.46  x  0.55 were

being prepared by a conventional dry ceramic method to

form the solid solution of a composition that follows:

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3. The re-

agent grade oxide of PbO, ZrO2, TiO2, La2O3, MoO3 and

In2O3 were used as starting materials in a stoichiometric

ratio. The powders were, first, ball-milled for twelve

hours; and, then, calcined at 800˚C for two hours at the

following heating and cooling rates: 2˚C/min. After cal-

cination, the mixture was, first, ball-milled for twenty-

four hours; and then, dried and granulated with PVA as a

binder. After drying, the powders were pressed into discs

of a diameter of thirteen millimeters and of a thickness of

about one millimeter. The compacted discs were being

sintered at a temperature ranging from 1000˚C - 1180˚C

for two hours in air. To prevent PbO volatilization from

the pellets, a PbO atmosphere was controlled with a bed

of PbZrO3 powder placed in the vicinity of the pellets.

The X-ray diffraction (XRD, Simens D500) was used

to determine the crystalline phases present in the powder.

The compositions of PZT phases were identified by the

analysis of the peaks [(002)T, (200)R, (200)T] in the

twenty range 43˚ - 46˚. The Cu Kα radiation with a step

of 0.01˚ was used. The bulk densities of the sintered ce-

ramics were being measured by the Archimedes method.

The micrographs of the fractured samples were taken on

a JEOL scanning electron microscope. The average grain

size of the samples was determined from the micrographs

by the linear intercept technique. To investigate the elec-

trical properties, the electrodes were made by applying a

silver paste on the two major faces of the sintered disks

followed by a heat treatment at 750˚C for thirty minutes.

The dielectric constant  was calculated from the capaci-

tance at a frequency of one kHz. It was measured at tem-

peratures ranging from 25˚C to 400˚C with a heating rate

of one ˚C/minute by using an impedance analyzer (HP

4192A, Hewlett-Packard). The piezoelectric samples were,

first, being poled in a silicone oil bath at 120˚C by apply-

ing a d.c. field of thirty kV/cm for thirty minutes; and,

then, were being cooled under the same electric field.

They were aged for twenty-four hours before testing.

The electromechanical coupling factor Kp, along with the

mechanical quality factor Qm were determined by the

resonance and anti-resonance technique from the equa-

tions [13]:



2.51























4





 





mar

QffRC

where:

fa: anti-resonant frequency (Hz)

fr: resonant frequency (Hz)

R: resonant resistance (ohms)

C: capacity (faraday)

3. Results and Discussion

The analysis of the phase was performed from the XRD

(at a room temperature) patterns over a range of 2θ = 43˚

to 46˚, where the tetragonal phase displays two peaks,

(002)T and (200)T, and the rhombohedral phase displays

one peak, (200)R. There was a broad region where the

two phases, the rhombohedral and the tetragonal, coex-

isted. This indicated a typical morpho-tropic phase be-

havior (MPB). The typical patterns of the X-ray diffrac-

tion of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3

compositions is shown in Figure 1. The samples ob-

tained in this study are summarized in Table 1. At

1150˚C, a typical tetragonal phase was observed at a

room temperature when xT  0.50. The (002)T and (200)T

peaks split into the (200)R peak as the ratio of Zr/Ti was

increased. The rhombohedral phase can be obtained

when xR  0.51. A transition from the tetragonal to the

rhombohedral phase was observed as the ratio of Zr/Ti

was increased. The Rhombohedral and the tetragonal

phases coexisted at x = 0.50 – 0.51, and demonstrated

that the ceramic resided at the morpho-tropic phase

boundary (MPB) [14]. The parameters of the lattice were,

then, determined from the triplets (200) by using a

non-linear least squares method [15]. The aR-parameter

of the rhombohedral phase and the aT-parameter, cT-pa-

rameter, and the tetragonality (cT/aT) of the tetragonal

phase of Pb0.95 La0.05[Zrx,Ti(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3

ceramics are plotted as a function of the ratio of Zr/Ti in

Figure 2. The results showed that the parameters of the

lattice of the tetragonal phase changed when the ratio of

Zr/Ti was modified. While the value of the aT parameter

increased, the one of cT parameter decreased, and the aR

parameter of the rhombohedral phase increased along

The Structure and the Electrical Properties of PbLa [Zr Ti (Mo ,In )]O Ferroelectric Ceramics 1201

0.95 0.05x(0.95–x)1/32/3 0.050.98753

Table 1. Series of compositions and crystal structure.

Crystal structure

Sample 1000˚C 1100˚C 1150˚C 1180˚C

Pb0.95 La0.05[Zr0.46Ti0.49(Mo1/3,In2/3)0.05]0.9875O3 T T - -

Pb0.95 La0.05[Zr0.47Ti0.48(Mo1/3,In2/3)0.05]0.9875O3 T + R T T -

Pb0.95 La0.05[Zr0.49Ti0.46(Mo1/3,In2/3)0.05]0.9875O3 T + R T + R T T

Pb0.95 La0.05[Zr0.50Ti0.45(Mo1/3,In2/3)0.05]0.9875O3 T + R T + R T + R T + R

Pb0.95 La0.05[Zr0.51Ti0.44(Mo1/3,In2/3)0.05] 0.9875O3 T + R T + R T + R T + R

Pb0.95 L0.05[Zr0.52Ti0.43(Mo1/3,In2/3)0.05]0.9875O3 T + R T + R R R

Pb0.95 L0.05[Zr0.54Ti0.41(Mo1/3,In2/3)0.05]0.9875O3 T + R T + R R -

Pb0.95 La0.05[Zr0.55Ti0.40(Mo1/3,In2/3)0.05]0.9875O3 R R - -

T = Tetragonal; R = Rhombohedral; T-R = Tetragonal-Rhombohedral.

(a) (b)

Figrue 1. XRD patterns of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics sintered at 1150˚C for 2h: (a) x = 0.52, (b) x

= 0.46, (c) x = 0.50 and (d) x = 0.51.

with the sintering temperature in the coexistence region.

The resulting values of the parameters of the lattice of

the tetragonal phase showed that the c

T/aT axial ratio

decreased as aT increased and cT decreased. The values

of the parameters of the lattice were revealed to be

practically the same as those previously studied [16,

17].

Figure 3 shows the SEM micrographs of

Pb0.95La0.05[Zr0.50Ti0.45(Mo1/3, In2/3)0.05]0.9875O3 ceramics

sintered at different temperatures. It can be observed

The Structure and the Electrical Properties of PbLa [Zr Ti (Mo ,In )]O Ferroelectric Ceramics

1202 0.95 0.05x(0.95–x)1/32/3 0.050.98753

Figure 2. The parameters of the lattice of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics as a function of composition

( for a sintering temperature about 1150˚C) .

Figure 3. SEM micrographs for Pb0.95La0.05[Zr0.50Ti0.45(Mo1/3,In2/3)0.05]0.9875O3 ceramics sintered at (a)1000˚C, (b) 1100˚C and

that many distinct pores exist on the surface of the

Pb0.95La0.05[Zr0.50Ti0.45(Mo1/3,In2/3)0.05]0.9875O3 ceramics

sintered at 1000˚C and the average grain size is under 9

m. When the sintering temperature is increased, the

pores can hardly be observed and the grain size is about 9

m. This indicates that a high sintering temperature

promotes a grain growth process. The obtained images

show a slight difference in the particle size and also give

rise to the different phases, viz. the tetragonal, the rhom-

bohedral, and the tetragonal-rhombohedral. In addition to

the morphological modification of grains, different grain

sizes could be noticed for these samples. In this way, the

coexistence region of the tetragonal-rhombohedral phases

was demonstrated.

The values of the room temperature of the dielectric

constant (



) and the dissipation factor (tan δ) at 1 kHz for

all samples are given in Figure 4. It can be seen that the



curve appears to be parabolic, and the values of



in-

crease sharply from 46/49 to 50/45; and, also, large di-

electric constants are obtained at the compositions of

50/45 (



= 430 at 1 kHz) and 51/44 (



= 390 at 1 kHz). It,

then, follows a decreasing trend when the ratio of Zr/Ti is

increased further. The present results verify the conclu-

sions about the dielectric constant peak in MPB. The

increase in Zr content induces the microstructure transi-

tion of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3

from the rhombohedral to the tetragonal phase within the

MPB region, as indicated by the above XRD investiga-

tions. The tan shows an inverse trend and reaches the

minimum value of 3.9% when x = 0.50. Thus the compo-

sitions at 50/45 and 51/44 are at the center of the MPB.

Figure 5 reveals the dielectric constant



as a function

of temperature for the

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics (x

= 0.50 and x = 0.51) sintered at 1150˚C, which were

measured at a frequency of 1 kHz. As it might be known,

two peaks are observed on the dielectric constant versus

temperature curves in the measured temperature which

ranges between 265˚C and 330˚C for a sample of a ce-

ramic 50/45. The first dielectric peak corresponds to the

transition temperature TR–T, of the rhombohedral to the

tetragonal phase, but the second peak, which results at a

The Structure and the Electrical Properties of PbLa [Zr Ti (Mo ,In )]O Ferroelectric Ceramics1203

0.95 0.05x(0.95–x)1/32/3 0.050.98753

Figure 4.The dielectric constant ε and the loss tangent (at

room temperature, 1 KHz) for

Pb0.95La0.05[Zrx,Ti(0.95–x)(Mo1/3, In2/3)0.05]0.9875O3 ceramics as a

function of composition.

Figure 5. The dielectric constant ε (at 1 KHz) for

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics as a

function of temperature.

higher temperature, is the Curie temperature Tc. The

broadening in the transition phase is attributed to the

structural disorder and the compositional fluctuation

present in the arrangement of cation at A-site and B-site

with lattice vacancies. This results in a microscopic het-

erogeneity in the composition and the distribution of

different local Curie points [18].

Figure 6 shows the variation of the electromechanical

coupling factor Kp and the mechanical quality factor Qm

for Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3, In2/3)0.05]0.9875O3 ceramics.

It is observed in Figure 6 that as the ratio of Zr/Ti in-

creases, the value of kp increases; and, subsequently,

represents a peak of 0.67 at the ratio of Zr/Ti of 50/45;

but, when the ratio of Zr/Ti is further increased, the

value of Kp decreases. Qm continues to decrease; and,

finally, shows the minimum value when the ratio of

Figure 6. The Coupling factor Kp and Qm for

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics sin-

tered at 1150˚C as a function of composition (x).

Zr/Ti is 50/45 (Qm = 20). This is due to the fact that the

structure of the phase of

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 ceramics

changes, first, from the tetragonal phase to the coexis-

tence of both the tetragonal and the rhombohedral phases;

and, then, changes to a single rhombohedral phase when

the ratio of Zr/Ti is increased.

4. Conclusions

The aim of this study was to investigate the structure and

the behavior of the electrical properties in

Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3. The phases

of the sintered samples were examined by X-ray diffrac-

tometry. The structure of the phase of the system was

changed from the tetragonal to the rhombohedral as the

ratio of Zr/Ti was increased. The XRD results reveal that

an MPB with the co-existence of the rhombohedral and

the tetragonal for the ceramics lies in the range of x =

0.50 – 0.51. The parameters of the lattice: aT and cT of the

tetragonal structure and aR of the rhombohedral structure

were found to change when composition is modified. The

Pb0.95La0.05[Zr50Ti45(Mo1/3,In2/3)0.05]0.9875O3 ceramics sin-

tered at 1150˚C exhibit good piezoelectric properties: Kp

= 0.67, Qm = 20 and TC = 335˚C. This means that this

system is a promising candidate for the lead-free piezo-

electric applications.

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