Investigation on the Microstructure and Electrical Properties of the Compositionally Modified PZT Ceramics Prepared by Mixed-Oxide Method

doi:10.4236/msa.2013.411091

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Materials Sciences and Applications, 2013, 4, 723-729

Published Online November 2013 (http://www.scirp.org/journal/msa)

http://dx.doi.org/10.4236/msa.2013.411091

Open Access MSA

723

Investigation on the Microstructure and Electrical

Properties of the Compositionally Modified PZT Ceramics

Prepared by Mixed-Oxide Method

Malika Abba, Ahmed Boutarfaia, Zelikha Necira, Noura Abdessalem, Hayet Menasra,

Abdelhek Meklid

Laboratory of Applied Chemistry, Department of Science Matter, University of Biskra, Biskra, Algeria.

Email: [email protected]

Received August 17th, 2013; revised September 29th, 2013; accepted October 16th, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

The structural and electrical properties of Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 piezoelectric ceramics system with the com-

position near the morphotropic phase boundary were investigated as a function of the Zr/Ti ratio. Studies were per-

formed on the samples prepared by the conventional method of thermal synthesis of mixed oxides. The materials struc-

ture was investigated by X-ray diffractometry to demonstrate the co-existence of the tetragonal and rhombohedral

phases. In the present system, the MPB, in which the tetragonal and rhombohedral phases coexist, is in a composition

range of 0.47 ≤ x ≤ 0.50. The lattice constants of the a and c axes for the samples were calculated from the XRD patterns.

Microstructure of the sintered ceramics was observed by scanning electron microscopy (SEM) of free surfaces speci-

mens. The relative permittivity, dielectric dissipation, piezoelectric coefficient and electromechanical coupling factor

reach at maximum value x = 0.49 (εr = 7300.345 (at the Curie temperature), tanδ = 0.002050, d31 = 94.965 PC/N and kp

= 0.513 and a Curie temperature of 430˚C). These properties are very promising for applications in ultrasonic motors.

Keywords: Morphotropic Phase Boundary; Sintering Temperature; Zr/Ti Ratio

1. Introduction

Lead zirconate titanate Pb(Zr,Ti)O3, a solid solution of

perovskite ferroelectric PbTiO3 and anti-ferroelectric

PbZrO3 with different Zr/Ti ratio, is an important mate-

rial that is widely used in electronic sensors, actuators,

resonators and filters [1-3]. The materials with a per-

ovskite structure of general formula ABO3 (where A =

mono or divalent ions, B = tri, tetra or pentavalent ions)

have been found to be very useful and interesting for

different solid-state devices [4-8]. By making suitable

substitution at A and/or B-site of ABO3 structure, a large

number of charge neutral or deficient compounds have

been prepared [9-11] which have been found to be very

suitable and useful for many industrial applications.

In order to satisfy the requirements of practical appli-

cations of ultrasonic motors, many ternary and quater-

nary solid-solutions such as: Pb(Mn1/3Nb2/3)O3-PZT,

Pb(Mn1/3Sb2/3)O3-PZT,Pb(Cd1/3Nb2/3)O3-PZT,

Pb(Mn1/3Nb2/3)(Ni1/3Nb2/3)O3-PZT, have been synthesized

by the modification or the substitution [12-18].

The influence of technological factors on the width of

the co-existence region was investigated on the ternary

system Pb[Zrx,Ti(0,95−x)(Mo1/3,In2/3)0.05]O3 by X-ray dif-

fraction by varying the ratio Zr/Ti. The purpose of this

work is to study the influence of sintering temperature on

density, porosity and grain size on the ceramic in order to

determine the width of co-existence of tetragonal and

rhombohedral phases and the exact composition of the

MPB rather than to determine the dielectric and the pie-

zoelectric properties of these ceramics near the MPB in

detail.

2. Experimental

All of the specimens were prepared by the conventional

ceramics technologie. The compositions of the

Pb[Zrx,Ti(0.95−x)(Mo1/3,In2/3)0.05]O3 system werewith 46 ≤ x

≤ 55. The commercially available PbO, ZrO2, TiO2,

MoO3 and In2O3, were used as the raw materials. Mixed

oxides, after milling, were calcined at 800˚C for 2 h at

heating and cooling rates of 2˚C/min. After calcinations,

Investigation on the Microstructure and Electrical Properties of the Compositionally Modified

PZT Ceramics Prepared by Mixed-Oxide Method

724

the ground and milled powders were pressed into disks

13 mm in diameter and about 1 mm in thickness. Pressed

disks of 3PbO + 2ZrO2 placed in a capped crucible to pre-

vent PbO evaporation during sintering. Four sintering con-

ditions were selected to be used with both methods rang-

ing 1000˚C, 1100˚C, 1150˚C, 1180˚C and 1200˚C for 2 h.

The crystal structure of the samples was analyzed us-

ing X-ray diffractometry (XRD; Siemens D500). The

voltage and currents ratings used were 40 kV, 30 mA

respectively, and CuKα radiation was used. The dif-

fraction data were collected with X-ray scan speed of

0.1˚·min−1. The bulk density was measured using the

Archimedes method.

To investigate the electrical properties, the electrodes

were made by applying a silver paste on the two major

faces of the sintered disks followed by heat treatment at

750˚C for thirty minutes. The dielectric constant ε was

calculated from the capacitance at a frequency of one

KHz. It was measured at temperature ranging from 25˚C

to 400˚C with a heating rate of one ˚C/minute by using

an impedance analyzer (HP4192A, Heweltt-Packard).

The piezoelectric samples firstly were being poled in a

silicone oil bath at 120˚C by applying a d.c. field of thirty

KV/cm for thirty minutes; and, then, were being cold

under the same electric field.

They were aged for twenty-four hours before testing.

The electromechanical coupling factor Kp was deter-

mined by the resonance and anti-resonance technique

from the “Equation (1)” [19].

()

2.51



×−



=





(1)

fa: anti-resonant frequency (Hz).

fr: resonant frequency (Hz).

3. Results and Discussion

3.1. Phase Structure

The sintered powders were examined by X-ray diffrac-

tometry to ensure phase purity and to identify the phases.

The phases of the samples were detected using XRD (at

room temperature) for several compositions given in Ta-

ble 1.

It is reported that tetragonal, rhombohedral and T-R

phases were identified by an analysis of the peaks 0 0 2

(tetragonal), 2 0 0 (tetragonal), 2 0 0 (rhombohedral)) in

the 2

range 43˚ - 47˚.

The splitting of (0 0 2) and (2 0 0) peaks indicates that

they are the ferroelectric tetragonal phase (T), while the

single (2 0 0) peak shows the rhombohedral phase (R)

Figure 1 [20].

Triplet peaks indicate that the sample consists of a

Table 1. Series of compositions and crystal structure.

Crystal structure

Sample 1000˚C 1100˚C 1150˚C 1180˚C

Pb[Zr0.46Ti 0.49(Mo1/3In2/3)0.05]O3 T T T T

Pb[Zr0.47Ti 0.48(Mo1/3In2/3)0.05]O3 T + R T T T + R

Pb[Zr0.49Ti 0.46(Mo1/3In2/3)0.05]O3 T + R T + R T + RT + R

Pb[Zr0.50Ti 0.45(Mo1/3In2/3)0.05]O3 T + R T + R T + RT + R

Pb[Zr0.51Ti 0.44(Mo1/3In2/3)0.05]O3 T + R T + R T + RR

Pb[Zr0.52Ti 0.43(Mo1/3In2/3)0.05]O3 T + R T + R T + RR

Pb[ Zr0.54Ti 0.41(Mo1/3In2/3)0.05]O3T + R T + R R R

Pb[Zr0.55Ti 0.40(Mo1/3In2/3)0.05]O3 R R R R

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

Figure 1. The XRD patterns of Pb

[Zrx,Ti(0.95−x)(Mo1/3,In2/3)0.05]O3 systemwith 0.46 ≤ x ≤ 0.55.

mixture of tetragonal and rhombohedral phases. The

multiple peak separation method was used to estimate the

relative fraction of coexisting phases by which the rela-

tive phase fraction MR and MT were then calculated using

the following Equations (2) and (3) [21]:

()

() () ()

200

200 002 200

RTT

MIII

=++ (2)

() ()

() () ()

200 002

200 002 200

RTT

MIII

= (3)

It is clear that, IR(200) is the integral intensity of the

(200) reflection of the rhombohedral phase and IT(200),

IT(002) are the integral intensities of the (200) and (002)

reflections of the tetragonal phase, respectively. A transi-

tion from tetragonal to rhombohedral phase is observed

as Zr/Ti ratio increases. With increasing Zr/Ti ratio,

tetragonal relative fraction decreases and rhombohedral

relative fraction increases.

At 1180˚C Figure 2, it is shown that the tetragonal

structure can be formed up to xT > 0.46, while the rhom-

bohedral structure becomes stabilized for xR < 0.51.

However, at x = 0.46 - 0.51 tetragonal and rhombohedral

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Investigation on the Microstructure and Electrical Properties of the Compositionally Modified

PZT Ceramics Prepared by Mixed-Oxide Method

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Figure 2. Variation of the relative content of the tetragonal

and rhombohedral phases with different Zr% in the

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 (for a sintering temperature

about 1180˚C) [20].

phases coexist. The co-existence region is therefore quite

narrow (Δx ≈ 0.05) and extends between xT and xR. The

width Δx = xT − xR of the co-existence region from our

work is close to that obtained by others [22,23]. The co-

existence of tetragonal and rhombohedral phases has,

therefore, to be attributed to the first order nature of the

MPB, this is marked contrast to the proposition of Kake-

gawa and al. [24,25] that the coexistence is invariably

due to compositional fluctuations.

The study of density is necessary to optimize the op-

timum sintering temperature. The quality of the material

increases with the increase of density and it increases

with the increase of the sintering temperature [26]. The

optimum temperature for sintering is determined from

the pattern density as a function of sintering temperature

d = f(T). So, the maximum density is the product of bet-

ter quality electrical (low dielectric loss). Figure 3 gath-

ers the curves of the density of all samples depending on

the sintering temperature. A similar shape for all curves

is that: the density is minimal for a sintering temperature

T = 1000˚C, it begins to grow until it reaches a maximum

value at a sintering temperature T = 1180˚C. Then, it

decreases at the sintering temperature T = 1200˚C which

means that the optimum temperature for sintering is

1180˚C. The increased density means fewer and pore size,

so the volume of the cell decreases and consequently the

structure becomes more compact.

The optimum sintering temperature depends on several

factors such as the addition of impurities, the rate of

heating, time of thermal treatment and protecting atmos-

phere.

Changes in the density of different samples of

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 sintered at 1180˚C de-

pending on the rate of Zr is shown in Figure 4.

The shape of the curve shows that the density increases

with the increase of Zr concentration until a maximum

Figure 3. Effect of sintering temperature on density for

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3.

Figure 4. Evolution of density as a function of the concen-

tration of Zr% [20].

value of 7.61g/cm3 (94.18% of theoretical density) at Zr =

49% (sample No. 3) and then it decreases [20].

Figure 5 shows the variation of the porosity for dif-

ferent samples depending on the concentration of Zr%

and the sintering temperature of 1180˚C, noting that the

porosity decreases until itreaches the minimum value p =

5.81% for Zr = 0.49 (sample No. 3) and then it increases.

The parameters of the lattice were determined from the

triplets (200) by using a nonlinear least squares method

[27]. The aR—parameter of the rhombohedral phase and

the aT—parameter, cT—parameter, and the tetragonality

(cT/aT) of the tetragonal phase of

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 ceramics are plotted as a

function of the ratio of Zr/Ti in Figure 6. The results

showed that the parameters of the lattice of the tetra-

gonalphase changed when the ratio of Zr/Ti was modi-

fied. While the value of the aT parameter increased, the

one of cT parameter decreased and the aR parameter of

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Investigation on the Microstructure and Electrical Properties of the Compositionally Modified

PZT Ceramics Prepared by Mixed-Oxide Method

726

Figure 5. The variation of porosity as a function of the con-

centration of Zr% for Pb [ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 (for a

sintering temperature about 1180˚C) [20].

Figure 6. The parameters of the lattice of

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 ceramics as a function of

composition(for a sintering temperature about 1180˚C) [20].

the rhombohedral phase increased. The resulting values

of the parameters of the lattice of the tetragonal phase

showed that the cT/aT axial ratio is decreased as aT it is

increased and cT is decreased. The values of the parame-

ters of the lattice were revealed to be practically the same

as those which previously studied [28,29].

Figure 7 gives the SEM micrographs of free surfaces

of the specimens sintered at 1000˚C - 1180˚C for 2 h.

From these images, small crystallites with large pores for

specimens sintered at 1000˚C Figure 7(a) were noticed.

As the sintering temperature increased, the grain grew

and the average grain size increased slightly. Whereas,

the number and the size of the pores is decreased. The

grain size exponentially increased with the increase of

temperature and this can be well explained by the phe-

nomenological kinetic grain grow equation [30]. The

average grain size is 1.15 µm at temperature 1000˚C

which increases to 1.56 µm at temperature 1180˚C [20].

Figure 7. SEM micrographs for

Pb[Zr0.50Ti0.45(Mo1/3,In2/3)0.05]O3 ceramics sintered at (a)

1000˚C, (b) 1100˚C (c) 1150˚C and (d) 1180˚C.

3.2. Dielectric and Piezoelectric Properties

The dielectric properties at room temperature are plotted

as a function of the Zr/Ti ratio in Figure 8. The ε in-

crease with the increase of Zr/Ti ratio. It achieves a

maximum value of 1331.955 only when x = 0.49 and

then it decreases significantly as the Zr/Ti ratio increases

further. The tanδ shows an inverse trend and reaches the

minimum value of 0.00205 when x = 0.49.

The temperature dependence of the dielectric constant

for Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O 3 ternary ceramics at 1

KHz is shown in Figure 9. It is observed in all the com-

positions as the temperature increase, the value of dielec-

tric constant increases and passes through a maximum (at

TC) and then decreases. The Curie temperature increased

from 340˚C to 440˚C in our choosing composition. The

maximum dielectric constant at MPB (x = 0.49) is about

7300.345.

The variation in dielectric constant with frequency for

Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 ternary ceramics is shown

in Figure 10. The plots show that the dielectric constant

decreases with an increase in frequency, showing disper-

sion in lower frequency rang. It attains a constant value

and remains independent of frequency. Thereafter, all the

samples reveal dispersion due to Maxwell-Wagner [31,

32] type interfacial polarization in agreement with Koop’s

phenomenological theory [33]. The high value of dielec-

tric constant observed at lower frequencies can be ex-

plained on the basis of space charge polarization due to

heterogeneous in structure like impurities, porosity and

grain structure [34].

The electromechanical coupling factor (kp) and the

piezoelectric coefficient (d31) are shown in Figure 11.

These properties were also strongly influenced by the

composition of the specimen. The highest d31 of 94.965

pC/N and Kp of 0.513 were observed for the composition

of x = 0.49. Considering that the fact of this composition

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Investigation on the Microstructure and Electrical Properties of the Compositionally Modified

PZT Ceramics Prepared by Mixed-Oxide Method

727

Figure 8. The dielectric constant ε and the loss tangent (at

room temperature, 1 KHz) for

Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 ceramics sintered at 1180˚C.

Figure 9. Temperature dependence of the dielectric con-

stant for Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 ceramics sintered

at 1180˚C (1 KHz).

Figure 10. Variation of dielectric constant with frequen-

cy for Pb[ZrxTi0,95−x(Mo1/3In2/3)0.05]O3 ceramics sintered at

1180˚C.

Figure 11. Variation of Kp and d31 for

Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 ceramics sintered at 1180˚C.

corresponds to the MPB and the maximum piezoelectric

properties observed for this polycrystalline composition

are reasonable. When the PZT content was varied away

from the MPB, both the d31 and kp value decreased

asymmetrically. In the rhombohedral side, both the d31

and kp value were decreased much more rapidly.

4. Conclusions

In this study, ceramics in the

Pb[ZrxTi0.95−x(Mo1/3In2/3)0.05]O3 system (with 0.46 ≤ x ≤

0.55) were successfully prepared by a solid-state mixed-

oxide technique. The co-existence region was investi-

gated by X-ray diffraction. The study of the morpho-

tropic phase boundary has established that the phase

transition from tetragonal to rhombohedral symmetry

takes place at x = 0.49 and the width of the phase bound-

ary that has been found to be in the range of 0.47 ≤ x ≤

0.50 at 1180˚C.

The lattice parameters aT and cT of the tetragonal struc-

ture and aR of the rhombohedral structure were found to

change with composition. The effect of the sintering

temperature on the density and grain size has been inves-

tigated. It was demonstrated that the grain size and the

density increased with the increase of the sintering tem-

perature. The optimum sintering temperature (1180˚C)

corresponds to the maximum density. So, the minimum

value of porosity is also corresponds to the better quality

product.

The electrical and piezoelectric properties exhibit a

compositional dependence. The samples showing the co-

existence of morphotropic phase boundary (MPB) ex-

hibit good properties. The results indicate that although

this kind of ceramics displays good properties, further

study is needed to improve their stabilities of the ceramics

in order to be utilized in various temperature environ-

ments.

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