Microstructure and Dielectric Properties of PZS-PLZT Ceramics System

doi:10.4236/msa.2013.48058

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Materials Sciences and Applications, 2013, 4, 478-482

http://dx.doi.org/10.4236/msa.2013.48058 Published Online August 2013 (http://www.scirp.org/journal/msa)

Microstructure and Dielectric Properties of PZS-PLZT

Ceramics System

Sakri Adel*, Boutarfaia Ahmed

Laboratory of Applied Chemistry, University of Biskra, Biskra, Algeria.

Email: *[email protected]

Received June 5th, 2013; revised July 8th, 2013; accepted July 17th, 2013

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

ABSTRACT

Piezoelectric ceramics are an important class of solid-state materials as they exhibit a wide range of applications. This

article investigates the sintering temperature effect on microstructure and dielectric properties of a new ceramics mate-

rial Pb (Zn, Sb) O3-PbLa (Zr, Ti) O3 (PZS-PLZT), which was prepared by a solid mixed-oxide solution method. Scan-

ning electron micrograph (SEM) and X-ray diffraction (XRD) techniques was employed to examine the crystallization

of the ceramics. The results of XRD show that the phase structure of the samples is tetragonal. The lattice parameters

and the density increased with increase of the sintering temperature. The dielectric constant and the dielectric loss of the

investigated samples decreased with increase in the frequency.

Keywords: Ferroelectric; Microstructure; Piezoelectric Ceramics; Dielectric Properties

1. Introduction

The piezoelectric property plays an important role for

electric and electronic materials. The most widely used

piezoelectric materials are based on the PbTiO3-PbZrO3

system (PZT) [1-3]. The application of the PZT compo-

nent is wide, including nonvolatile memory elements,

pyroelectric detectors, piezoelectric transducers, and pho-

toelectric devices [4,5], but the electrical and thermal

properties of PZT ceramics depend to a large extent on

their surface microstructures [6]. Many researchers have

considered modified PZT compositions with suitable

substitution at the A and B sites [7-9] with some dopants

to improve their electrical and mechanical property of

piezoelectric materials in recent years, this dopants can

be classified into two categories: donor dopants which

induce Pb vacancies by changing with a higher valence

ion for Pb2+ or (Ti, Zr)4+ like Sb5+, La3+. And the acceptor

dopants induce O vacancies by changing with a lower

valance ion for Pb2+ or (Ti, Zr)4+ example K+, Fe3+ [10,

11]. So the properties of a PZT samples are very sen-

sitive to additives, composition and synthesis methods.

Whatmore et al. [12] and Chaipanich et al. [13] have

reported that the electric properties of PZT ceramics

could be improved by the doping of Sb2O3. [14]. It was

found that sintering behavior had obvious effects on the

microstructure and piezoelectric properties. With the in-

crease of sintering temperature, the microstructure of the

ceramic samples changed accordingly and the porosity

decreased [15].

There have been several reports on La substituted PZT.

It has been reported that substitution of Pb2+ by La3+ ions

created vacancies in the A site of perovskite ABO3

structured PZT ceramics. The 7% La doped PZT ceram-

ics PLZT (7/60/40) composition is one of the most im-

portant candidates for piezoelectric applications due to its

extremely high piezoelectric and electromechanical cou-

pling coefficients reported in literature [16-18].

In this work, a new ceramics material based PZT is

prepared by a solid mixed-oxide solution method, and we

investigate the structural, dielectrical properties of a

doped PZT ceramic with La, Sb and Zn for different sin-

tered temperature.

2. Experimental

The composition of PZS-PLZT system was 0.3Pb(Zn1/3,

Sb2/3)O3-0.7Pb0.98La0.02(Zr0.48,Ti0.52)O3 were synthesized

from high purity oxide powders PbO (99.90%), ZrO2

(99.90%), TiO2 (99.80%), Sb2O3 (99.90%), ZnO

(99.90%), and La2O3 (99.90%), the samples were pre-

pared by the conventional ceramic procedure. Stoichio-

metric amount of metal for the designated PZS-PLZT

*Corresponding author.

Microstructure and Dielectric Properties of PZS-PLZT Ceramics System

479

composition was mixed for 2 hours as the grinding media

and ethanol as the solvent. After milling for 6 hours, the

resultant slurry was dried in an oven and then the pow-

ders were calcined in a high-temperature furnace at

850˚C for 120 min. Then, the calcined powder was ball-

milled again to ensure a fine particle size for 6 hours.

After drying, the powder was pressed as disks and sin-

tered at two different temperatures 1050˚C and 1200˚C in

a closed aluminum crucible, the atmosphere was en-

riched in PbO vapor using PbZrO3 powder, the density of

the sintered component was measured from its mass and

dimensions. The sintered discs were next mechanically

processed by abrasion, dried and electrified with a silver

paste burned out at 700˚C for 30 min. The polling was

carried out in a silicon oil bath at 100˚C under an electric

field of 3 kV/mm and cooled down to room temperature

still being under the influence of the electric field. They

were aged for 24 h prior to testing. The temperature de-

pendence of dielectric properties was measured at tem-

peratures ranging from room temperature to 650˚C with a

heating using an impedance analyzer. An X-ray diffract

meter BRUKER-AXE, D8 with CuKα radiation (λ =

1.5406 Å). Using the JCPDS database we can identify

the presence of the perovskite structure and phases of the

sintered samples. Surface microstructures of the ceramics

were observed using a scanning electron microscopy

(SEM) (JEOL JSM-6390LV) at room temperature.

3. Results and Discussion

3.1. X-ray Diffraction (XRD)

The XRD patterns of PZS-PLZT ceramics shown in

Figure 1 were identified as a material with perovskite

structure having tetragonal symmetry according to

JCPDS (Joint Committee of Powder Diffraction Stan-

dards) card n 00-046-0504. The tetragonal lattice pa-

rameters were determined from the evolution of the

tetragonal peaks (200) and (002) by using CELREF

software.

The results given in Table 1 revealed that the tetrago-

nal cell parameters are associated with some physical

properties of the sintered samples. The lattice parameters

and the density increased with increase the sintering tem-

perature.

3.2. Scanning Electron Micrograph (SEM)

Figure 2 shows the scanning electron micrograph (SEM)

microstructure of the porous PZS-PLZT prepared sam-

ples sintered at 1050˚C and 1200˚C by (SEM: JEOL

JSM-6390LV). The increase of grain size from ≈1.83 µm

to ≈3.12 µm is observed significantly with the increasing

of sintering temperature from 1050˚C to 1200˚C respec-

tively, and it can clearly be seen that the prepared PZS-

PLZT ceramics is porous and has a not uniform distribu-

tions of grain shape and size.

Figure 1. XRD patterns of PZS-PLZT ceramics sintered at (a) 1050˚C and (b) 1200˚C.

Table 1. Some physical properties of the sintered PZS-PLZT ceramics.

lattice parameters

Sintering temperature (˚C) Thickness [cm] Diameter [cm] specific weight [g/cm3] phase

a [Å] b [Å] c [Å]

1050˚C 0.18

1.20

6.635

T 4.0155 4.0155 4.0517

1200˚C 0.18

1.15

7.598

T 4.0346 4.0346 4.0714

Microstructure and Dielectric Properties of PZS-PLZT Ceramics System

480

Figure 2. SEM micrographs of PZS-PLZT ceramics sintered at (a) 1050˚C; (b) 1200˚C for 2 hours.

Figure 3. Temperature dependence of ɛr for PZS-PLZT

samples sintered at 1050˚C and 1200˚C.

3.3. Dielectric Properties and the Loss Factor

Figure 3 shows the variation of the dielectric constant at

5 kHz with increment of temperature for the two samples

witch sintered at 1050˚C and 1200˚C. Similar to normal

ferroelectrics, the dielectric constant increases gradually

with increasing temperature up to the transition tem-

perature, then it decreases. Here we can note the most

important characteristic of a disordered perovskite struc-

ture. The dielectric constant reaches a maximum value of

19,130 (Tc = 500˚C) for sample sintered at 1050˚C, but

for the sintering temperature 1200˚C, the dielectric

constant continues increasing (out of range temperature

Tc > 650˚C). There, may be that this result is due to the

change in the bulk density and the grain morphology

with the change of sintering temperature [19]. This

constant decreases gradually with increasing frequency

(Figure 4) it reaches a maximum value at small values of

frequency which explained by existence of different

polarization models [20,21]. The dielectric constant of

Figure 4. Frequency dependence of ɛr for PZS-PLZT sam-

ples sintered at 1050˚C and 1200˚C.

Figure 5. Temperature dependence of Tangδ for PZS-PLZT

samples sintered at 1050˚C and 1200˚C.

sample sintered at 1200˚C decreases slowly than of

Microstructure and Dielectric Properties of PZS-PLZT Ceramics System

481

Figure 6. Frequency dependence of Tangδ for PZS-PLZT

samples sintered at 1050˚C and 1200˚C.

1050˚C sintered sample.

Figure 5 shows the variation of the loss factor Tangδ

with temperature. Tangδ increases gradually with in-

creasing temperature. For sintered temperature 1050˚C

the loss factor reaches a maximum value of 0.65 at (Tc =

550˚C), but for the sintering temperature 1200˚C, the

dielectric constant continues increasing (out of range

temperature Tc > 650˚C). This may be caused by the

losses due to the electrical conduction. This factor de-

creases with increasing frequency (Figure 6), which is a

characteristic of ferroelectrics [22,23].

4. Conclusion

PZS-PLZT was successfully prepared by a solid mixed-

oxide solution method; The X-ray diffraction measure-

ments for all 0.3Pb(Zn1/3,Sb2/3)O3-0.7Pb0.98La0.02(Zr0.48,

Ti0.52)O3 sintered samples indicated the presence of te-

tragonal phase and the scanning electron micrograph

shows a porous nature of ceramics and the grain size

increases with increasing the temperature. The influence

of the sintering temperature on the properties of PZS-

PLZT ceramics was studied. The lattice parameters and

the density increased with increase of the sintering tem-

perature. The dielectric constant and the dielectric loss of

the sintered samples decreased with increase in the fre-

quency. The effects of the sintering temperature on the

dielectric properties can be attributed to the change in the

bulk density and the grain morphology with the change

of the sintering temperature.

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