Synthesis of nano crystalline spatulae of lead zirconate titanate (PbZr0.52Ti0.48O3)

doi:10.4236/ns.2010.21002

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Vol.2, No.1, 12-17 (2010) Natural Science

http://dx.doi.org/10.4236/ns.2010.21002

Synthesis of nano crystalline spatulae of lead zirconate

titanate (PbZr0.52Ti0.48O3)

S. S. Bhatt*, S. C. Chaudhry, Neeraj Sharma, Sonia Gupta

Department of Chemistry, Himachal Pradesh University, Shimla, India; [email protected]

Received 15 October 2009; revised 29 October 2009; accepted 2 November 2009.

ABSTRACT

A simple and effective method for the synthesis

of nano-crystalline PZT spatulae has been re-

ported near MPB via a new Solution-Ignition

Synthesis route and has been characterized by

FT-IR, XRD, TG/DTG/DTA and SEM techniques.

X-ray line broadening and Scherrer formula

show crystallite size to be~20 nm. Densities of

nano-crystalline spatulae of PZT in pellet form

made by using 2% PVA and without PVA have

been found to be 5.35 and 7.51 gm/cm3 respec-

tively compared to the theoretical value of 7.78

gm/cm3. Dielectric constants of 83 and 227 of

these spatulae with dielectric loss 0.118 and

0.0609 at 1 MHz and a high resistivity value of

3.043 * 107 Ω cm for PZT pellets made without

PVA suggest these nano-crystalline PZT spatu-

lae to be the potential candidates for high fre-

quency applications.

Keywords: Nanostructures; Chemical Synthesis;

Infrared Spectroscopy; X-ray Diffraction; Dielectric

Properties

1. INTRODUCTION

In advanced ceramics technology, the production of

good quality powders using different synthetic routes

has always been an essential requirement to obtain mate-

rials with desired properties, purity and stoichiometry. It

is because of an ever-increasing pace of development of

various technological innovations to sustain competitive

advantage, that various synthetic methods such as self-

propagating high temperature synthesis (SHS) [1], sol-

gel [2], hydrothermal [3-6], solution combustion synthe-

sis (SCS) [7] and wet grinding solid state thermal reac-

tion (a combination of SHS and SCS methods) [8] have

been reported in literature for the preparation of inor-

ganic oxide materials. Metal oxide of composition

PbZr0.52Ti0.48O3, synthesized by sintering process be-

tween 1200°C and 1300°C is known to be quite impor-

tant for technological applications due to its ferroelectric

and piezoelectric properties near morphotropic phase

boundary (MPB) [9,10]. For multilayer components and

thick film devices, it is desirable to bring down its sin-

tering temperature, thereby reducing energy consump-

tion and PbO evaporation.

In view of these interesting reports, we have therefore

made an attempt to synthesize nano-crystalline spatulae

of lead zirconate titanate, PbZr0.52Ti0.48O3, near mor-

photropic phase boundary (MPB) by a novel method,

solution ignition synthesis (SIS). This method is better

than other methods in a way that by igniting the solution

drop-wise, the surface area is increased and heat pro-

duced during ignition is sufficient to rise the internal

temperature per ignited drop, thereby reducing the over-

all high temperature sintering requirement for the ce-

ramics.

2. MATERIALS AND METHODS

2.1. Chemicals

The starting materials used for the preparation of lead

zirconate titanate powder i.e. lead acetate Pb (CH3COO)2.

3H2O, zirconyl nitrate ZrO(NO3)2 H2O and titanium tetra

isopropoxide Ti [(OPri

4] were of E Merck and used as

such without further purification.

2.2. Preparation of ‘As-Ignited Powder’

A solution of lead acetate Pb(CH3COO)2. 3H2O (5 gm,

0.0131 mol) in acetic anhydride was added drop-wise to

a mixture solution of ZrO(NO3)2. H

2O, (1.5848gm,.

00685 mol) and titanium tetra isopropoxide Ti(OPri)4,

(1.7984 gm, 0.006326 mol) dissolved in the same sol-

vent, with continuous stirring and a temperature of 60oC

during the course of addition was maintained. The re-

sulting clear mixture solution was then ignited by drop-

wise addition over aperiod of 4-5 hours into preheated

silica crucible kept at 200oC. Yellow colored solid mass

formed during the course of addition was scratched from

the walls of silica crucible after cooling it to room tem-

perature. It was finally grinded to a fine powder and la-

beled as “as-ignited powder”. The post annealing of the

S. S. Bhatt et al. / Natural Science 2 (2010) 12-17

“as-ignited powder” was done in an electric furnace at

600oC and 700oC for four hours in each case.

2.3. Instrumentation

FTIR spectra were scanned in KBr pellets using single

grating Nicolet 5700 series FTIR spectrophotometer in

the range of 4000-200 cm-1. Thermal analysis curves

(TGA/DTG/DTA) of the synthesized powders were re-

corded on a double pan SHIMADZU DTG-60H (simul-

taneous TG/DTA module) thermal analyzer. The ther-

mocouple used was Pt/Pt-Rh (10%) with a temperature

range from ambient to 1300٥C. The thermal investiga-

tions were carried out by heating the sample in a Pt cru-

cible in nitrogen atmosphere and using -Al2O3 as ref-

erence. A heating rate of 20٥C min-1 was employed. The

instrument calibration was checked periodically with a

sample of CuSO4.5H2O. Powder X-Ray Diffraction pat-

terns were recorded on PANalytical XPERT-PRO dif-

fractometer system using a typical wavelength of

1.54060 Ao (Cu-K radiation). The diffraction angle 2θ

was varied from 10-70o. The morphology, exact size and

shape of the lead zirconate titanate (PZT) particles were

determined by recording FESEM of PZT powder an-

nealed at 700oC on Hitachi S-4700 model.

For electrical measurements, two types of pellets, one

by using 2% PVA as binder and other without PVA, were

made from nano-crystalline PZT spatulae annealed at

700oC. Pelletization was done by applying 15 tons of

pressure on nano PZT powder put into a circular dye,

from a hydraulic press for 5 minutes and then sintered at

700oC. Both the sides of the sintered pellets were

cleaned, smoothened with a very fine sand paper and

electroded by applying silver paste. Current Voltage (I-V)

measurements were made by using two probe method on

Kaithley Source Meter (Model 2611), while dielectric

studies were done by measuring capacitance of the sam-

ple with metal-insulator-metal (MIM), Agilent 4285A,

75 KHz to 3 MHz precision LCR meter.

3. RESULTS AND DISCUSSION

The synthesis of nano-crystalline PZT powder of com-

position Pb(Zr0.52Ti0.48)O3 near MPB by Solution-Ignition

Synthesis has been shown in Figure 1.

3.1. FTIR Studies

A perusal of the FTIR spectra of as-ignited PZT powder

(Figure 2a) shows no absorption bands at 2912cm-1,

1652cm-1 and 1560 cm-1 attributed to νC-H and νC=O

modes of acetate group indicating complete ignition of

organic material used for the synthesis of samples. The

absorption bands occurring at 1428 cm-1 and 1110 cm-1,

may be ascribed to νC-O modes of the trapped atmos-

pheric carbon dioxide in the PZT material [11]. Interest-

ingly, the intensity of these two bands decreases signifi-

cantly when annealed at 600oC (Figure 2b) and disap-

pears completely at 700oC (Figure 2c). Another distinct

absorption band observed at 563 cm-1 has been assigned

to νM-O mode which is characteristic of the formation of

ABO3 type of perovskite structure of PZT powder [12].

The effect of annealing at 600oC and 700oC on the char-

acteristic bands is apparent from the shift of νM-O band

from 563cm-1 to higher wave numbers, 590cm-1 and

592cm-1 respectively, presumably due to increased

number of M-O bonds in the perovskite phase of PZT

material. In addition, the band at 592cm-1 in the sample

annealed at 700oC has been found to be more intense

than the band at 590cm-1 annealed at 600oC, confirming

thereby the formation of more of perovskite phase at

higher temperature.

Figure 1. Scheme for the preparation of lead zirconate ti-

tanate powder by solution-ignition synthesis (SIS).

Figure 2. FTIR spectra of a) as-ignited PZT powder; b)

powder annealed at 600oC; c) powder annealed at 700oC.

S. S. Bhatt et al. / Natural Science 2 (2010) 12-17

3.2. Thermal Analysis

Thermo analytical curves (TG/DTG/DTA) for as-ignited

PZT powder (Figure 3 blue in color) show only one step

decomposition in the range 275.93oC to 331.77oC with a

weight loss of only 1.005% as is also substantiated by

only one peak in DTG at 311.52oC and an endothermic

peak at 307.51oC in DTA curve indicated the escape of

carbon dioxide gas trapped in as-ignited PZT powder.

The TG/DTA curves (Figure 3 red in color) of as-ignited

powder annealed at 600oC, however, has shown neither

any weight loss in TG nor any peak in DTA curve indi-

cating the complete removal of carbon dioxide gas

trapped in the lattice of nano-crystalline PZT powder.

3.3. XRD Studies

Powder XRD pattern of as-ignited PZT powder (Figure

4a) shows broad and an ordered arrangement of peaks,

indicating the formation of nano-crystalline lead zircon-

ate titanate, presumably resulting from the internal heat

produced during drop-wise ignition of the reaction mix-

ture solution. Further, the pyrochlore phase which was

present initially at 28.5o 2θ with relative intensity of 100%

(657 counts) in as-ignited PZT powder (Figure 4a) gets

significantly reduced at 600oC and completely trans-

formed into perovskite phase at 31.0538o 2θ value after

annealing at 700oC (Figures 4b and 4c). Apparently,

therefore, the results of the PXRD patterns of as-ignited

PZT powder coupled with FTIR and thermo analytical

curves suggest that the solution ignition synthesis (SIS)

is a novel method of synthesis of nanocrystalline PZT

spatulae.

Indexing of the XRD patterns of nano-crystalline PZT

powder annealed at 700oC (Figure 4c) has been done by

matching them with the patterns of known PZT powder

of composition Pb(Zr0.52Ti .4 8)O3 [13,14]. Lattice pa-

Figure 3. Thermal analysis (TGA/DTA/DTG) curves of

as-ignited PZT powder (red) and PZT powder annealed at

600oC (blue).

Figure 4. Powder X-ray diffraction patterns of: a)

as-ignited PZT Powder; b) PZT powder annealed at

600oC; and c) at 700oC (-Perovskite phase and-Py-

rochlore phase).

rameters of the sample annealed at 700oC (c=4.32159Ao

and a=b= 4.06907Ao ) obtained from (001) and (100)

reflections at 20.5522o and 21.8429o 2θ values respec-

tively in XRD pattern with slight lattice distortion (c/a)

values to be 1.0620 have been found to be very close to

that of 1.066 of pure tetragonal phase [15]. Further, the

sharpness of the diffraction peaks in the XRD pattern

(Figure 4c) suggests better homogeneity and crystallin-

ity of the nano PZT spatulae. It is pertinent to mention

here that with the increase in annealing temperature of

as-ignited powder from 600oC and finally to 700oC, a

substantial increase in the intensity (counts) of the

perovskite (110) orientation has been observed thereby

confirming the enhanced crystallinity.

S. S. Bhatt et al. / Natural Science 2 (2010) 12-17

The relative amounts of perovskite and pyrochlore

phases (Table 1) have been determined from the relative

intensity of XRD peaks by using following equation [16]:

(110)

(110) (pyro)

% perovskite phase = I I

where I(110)-relative intensity of the peak due to (110)

orientation and I(pyro)-relative intensity of pyrochlore

phase. A perusal of the results in Table 1 indicates that

amount of pyrochlore phase decreases while the

perovskite phase increases with the increase in annealing

temperature.

Apart from the tetragonal phase depicted from the

XRD pattern of the PZT powder annealed at 700oC, the

relative percentage of rhombohedral and tetragonal

phases has been calculated from the triplets of the type

(002)T, (200)R and (200)T appearing at 44o-46o 2θ range

in the XRD pattern [17] using relation:

(200)

(200) (200)(002)

RTT

III



where PR represents rhombohedral phase, IR (200) is inten-

sity of (200) reflection of rhombohedral phase, IT (200)

and IT (002) is intensity of (200) and (002) reflections of

tetragonal phase. The results show that percentage of

rhombohedral and tetragonal phase in the present nano-

crystalline PZT powder is 30% and 70% respectively

indicating thereby that the chemical composition of syn-

thesized nano-crystalline PZT powder lies near to Mor-

photropic Phase Boundary.

3.4. Crystallite Size, Shape and Density

3.4.1. Size

Broadening of the peaks observed in the XRD patterns

(Figures 4a-4c) indicates particles in the nano range.

Crystallite size of the nano-crystalline PZT powder an-

Table 1. % phases in the nano-crystalline PZT powder samples.

No. Name of Sample %

Perovskite

Pyrochlore

1 As-ignited powder 36.10 63.89

2 Powder annealed at

600oC 71.81 28.18

3 Powder annealed at

700oC 97.43 2.57

nealed at 600oC and 700oC has been calculated by using

Scherrer Equation i.e.

Crysttalite size = cos







where k is the constant of proportionality (Scherrer con-

stant) and depends on how the width line is determined

and value of k is generally taken as 0.9. λ represents the

wavelength of the X rays and has a value of 1.54060Ao,

θ is the half of the angle (2θ) of diffraction and β is the

value of broadening of (110) line at Full Width Half

Maximum (FWHM) of in radians and has been found to

be 13.6 nm which increases to 21.4 nm respectively.

Such an increase in the crystallite size with increase in

annealing temperature finds support from earlier reports

in literature [18,19].

3.4.2. Shape

FESEM of the nano-crystalline PZT powder annealed

at 700oC (Figure 5) shows a mixture of both spherical

particles and stacks of nano spatulae of about 204 nm

in width. The spherical nature of the crystallite has

been attributed to the high pressure exerted by the

evolution of gases such as CO2, N2, O2, etc. during the

course of ignition reaction [20] while the formation of

stacks of nano spatulae may be attributed to the partial

melting and subsequent solidification during drop-

wise ignition of the PZT powder in the preheated sil-

ica crucible.

Figure 5. FESEM of nano-crystalline PZT spatulae.

S. S. Bhatt et al. / Natural Science 2 (2010) 12-17

3.4.3. Densities and Porosity

Densities of pellets of nano-crystalline PZT powder (one

made with 2% PVA as a binder and other without PVA

each of 15 mm in diameter and 1.3 mm thickness) meas-

ured by Archimedes Principle have been found to be

5.35 and 7.51 gm/cm3 respectively. These densities are

68.76% and 96.5% of the theoretical value (7.78

gm/cm3). The percentage porosity of PZT pellets has

been calculated from the relation:

% (1)100porosity  



where ρ and ρo are the experimental and the theoretical

densities of PZT (7.78 gm/cm3) and have been found

to be 31.24 % and 3.48 %.

3.5. Electrical Properties of Lead Zirconate

Titanate of Composition Pb (Zr0.52Ti 0. 48)O3

3.5.1. D. C. Resistivity

Resistivity has been obtained from current-voltage

studies of the pellet prepared from nano-crystalline

PZT powder annealed at 700oC by the two probe

method using a Keithley Source meter (Model 2611).

From a plot of Current vs Voltage (Figure 6) resis-

tance ‘R’ has been calculated from the slope of the

plot as, ()

slope RV

 and the resistivity ‘ρ’ using

the well known relation, (ohm meter)





where

A represents the area of the cross section and d is the

thickness of the pellet.

A high resistivity value of 3.043 * 107 Ω cm found in

the present studies has been attributed to the stoichio-

metric composition, better crystal structures and im-

proved microstructures obtained by this new solution

ignition synthesis (SIS) technique. The higher value of

resistivity is also of significant importance as it makes

this nano-crystalline PZT spatulae suitable for high fre-

quency application.

Figure 6. Current (I) vs Voltage (V) plot of nano-crystal-

line PZT pellet.

3.5.2. Dielectric Studies

The dielectric constant (ε) and dielectric loss (tan δ) of

sintered pellets of nano-crystalline PZT spatulae (with

2% PVA and without PVA) as function of frequency at

different temperatures have been studied and trends are

shown as graphs in Figures 7a and 7b. The values of 83

and 227 for dielectric constant and 0.118 and 0.0609 for

dielectric loss have been found at a frequency of 1MHz

which remains nearly same in the higher frequency

range (up to 3MHz). Further, a comparison of the values

of both dielectric constant (227 and 249) and dielectric

loss (0.0609 and 0.042) at 298 K and 373 K respectively

at constant frequency of 1MHz (Figure 8) shows an

increase in dielectric constant with decrease in dielectric

loss values. These observed low values of dielectric con-

stants have been found to be in agreement with the fact

that small grains attain low values of dielectric constant

and can stabilize dielectric relaxation up to higher fre-

quency region [21]. These studies also indicate that nano-

crystalline spatulae of lead zirconate titanate, Pb

(Zr0.52Ti 0.48)O3 synthesized near MPB with almost same

values of dielectric constant and dielectric loss over a large

range of frequencies (up to 3 MHz) may find their role as

successful and stable dielectrics in the field of electronics.

(a) (b)

Figure 7. Variation of dielectric constant and dielectric loss with frequency at room temperature for: a) PZT pellet with

2% PVA; and b) PZT pellet without PVA.

S. S. Bhatt et al. / Natural Science 2 (2010) 12-17

Figure 8. Variation of dielectric constant and dielectric loss

with temperature at 1 MHz frequency for PZT pellet without

PVA.

4. CONCLUSIONS

The present work describes a simple, effective and novel

synthetic strategy namely Solution Ignition Synthesis

(SIS) route for the preparation of nano-crystalline PZT,

which is advantageous over other commonly employed

methods. The FTIR and XRD patterns of the nano crys-

talline PZT spatulae confirmed their perovskite structure

near MPB. The dielectric constant and high values of

resistivity also suggest that they may find their role as

potential materials suitable for high frequency applica-

tions and as stable dielectrics.

5. ACKNOWLEDGEMENTS

The authors wish to acknowledge University Grants

Commission, New Delhi and Department of Science and

Technology, GOI for providing necessary instrumenta-

tion facilities and financial support in the form of SAP

and FIST programs to the Department of Chemistry.

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