Effect of Sn4+ Doping At B-Site on Structural and Electrical

Properties of PZT Ceramics

K Rama Rao1*, K S R Murthy2, M.N.V Ramesh2 and M. Chaitanya Varma2 1Department of Physics, Dr. V. S. Krishna Govt. Degree (A) and PG College, Visakhapatnam, India

2Department of Physics, Institute of Technology, GITAM (Deemed to be University), Visakhapatnam, India

*Corresponding author email: dattasairamu@gmail.com

Abstract: Tin doped PbTi0.48Zr0.52O3 samples have been synthesized using ceramic method. These exhibited

better impedance and dielectric constant values. The increase in dielectric constant has been attributed to Sn4+

occupying B-sites in the lattice. From rietveld XRD refinement, it has been observed that all samples shows

tetragonal lattice but with minor presence of PbO. Curie temperature has been measured from the variation of

dielectric constant with temperature. With increase in Sn content, Curie temperature has been observed to

decrease.

INTRODUCTION

Lead zirconate titanate (PZT) is the most common piezoelectric ceramic which shows excellent properties is

widely reported [1]. Piezoelectric Pb(Ti,Zr)O3 solid solutions (PZT) ceramics are widely used because of their

superior piezoelectric properties even though there are some disadvantages like the hazardous Pb element. New

compounds are being discovered or developed to replace the PZT ceramics but their dielectric properties are

not at the level of PZT compounds. A distinctive feature of PZT is its large piezoelectricity. PZT has a

perovskite-type crystalline structure, which is represented by the compositional formula ABO3, and the

structure is suitable to achieve large piezoelectricity. Piezoelectric properties around MPB (morphotropic phase

boundary) between the tetragonal and rhombohedra phases provide enormous electromechanical coupling

around that composition range. In case of PZT, PbTi0.48Zr0.52O3 composition has been found to exhibit high

values of d33 and dielectric properties [1]. The phases of PZT are easily controlled by the compositional change

of the zirconate and titanate ratio in several situations. Also, various doping elements change PZT’s properties

drastically by substituting on the cation sites. In this work we have selected Sn4+ for controlling the dielectric

properties of PbTi0.48Zr0.52O3, so that the dielectric constant can be increased and loss can be decreased [2] .

Experimental:

Sn doped PbTi0.48Zr0.52O3 compounds have been synthesized by standard ceramic method using PbO, ZrO2,

TiO2 and SnO2. Oxides are mixed in stoichiometric ratios in agate mortar for 10 hours. Samples were calcined at

950 deg C for 4 hours in muffle furnace at a heating rate of 5degC/min. The calcined powders were ground

again for 5 hours to increase the homogeneity and pressed into pellets of thickness 1mm and diameter 10mm.

These were sintered at a temperature of 1150deg C for two hours.

X-ray diffraction analysis have been performed using X’pert High score diffract meter, surface analysis have

been measured using Scanning Electron microscope, impedance measurements are taken using N4L impedance

analyser.

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Results:

Rietveld analysis of powder X-ray diffraction data of all the three samples have been done using MAUD

program [3]. The rietveldanalysis clearly shows the tetragonal structure corresponding to P4mm space group [4].

Due to excess PbO that has been mixed to compensate the loss of Pb during sintering, an extra peak

corresponding to PbO has been identified.

Figures 1a to 1c : Rietveld refined XRD pattern of the samples

Table 1: Lattice parameters

Samples Lattice parameter a,

angstroms

Lattice parameter c,

angstroms

Pb(Zr0.52Ti0.48)O3 3.9852 4.1378

Pb(Zr0.52Ti0.48)0.95 Sn0.05O3 4.0389 4.1248

Pb(Zr0.52Ti0.48)0.9 Sn0.1 O3 4.0589 4.0929

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The variation observed in the lattice parameters clearly shows that tin is occupying B-sites. The disappearance of

peak splitting of the highest intensity peak shows that tetragonal structure is becoming more dominant with the

increase in Sn4+ concentration. The increase in volume of the lattice with Sn4+ may tend to increase the dielectric

constant and further influence the losses with frequency or temperature.

Scanning Electron microscopy:

Figures 2a to 2c: Scanning electron micrographs of Sn doped PZT

The grain size has been calculated using linear intercept method [5] SEM pictures depict the formation of

tetragonal lattice as the shape of the grains is almost tetragonal. From these images it can be understood that

with the increase in Sn4+ concentration, there is a shift at the morphotropic phase boundaries (MPB) to

tetragonal structure.

Table 2: Grain size

Samples Grain Size (µm)

Pb(Zr0.52Ti0.48)O3 1.33

Pb(Zr0.52Ti0.48)0.95 Sn0.05O3 3.21

Pb(Zr0.52Ti0.48)0.9 Sn0.1 O3 3.42

With increase in Sn, grain size is observed to increase; this is due to increase in sinter ability of tin. As the

melting temperature of Sn is less [6] , it leads to decrease in sintering temperature and so grain growth occurs

and so an increase in grain size is observed.

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EDAX:

Figure 3a to 3c EDAX spectra of Sn doped PZT

Element Wt % At %

O K 19.39 64.41

TiK 7.02 7.78

PbL 46.22 11.85

ZrK 27.38 15.95

Table 3a to 3c: Compositional data from EDAX spectra

Energy dispersive x-ray spectra clearly present that there are no impurities other than Pb, Ti, Zr, and Sn. All the

elements as obtained from EDAX spectra show the presence of stoichiometry in these samples.

Element Wt % At %

O K 12.62 55.88

SnL 1.91 1.14

TiK 6.26 9.26

PbL 63.95 21.87

ZrK 15.26 11.85

Element Wt % At %

O K 16.98 64.29

SnL 3.31 1.69

TiK 6.51 8.23

PbL 61.37 17.94

ZrK 11.83 7.86

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Dielectric properties:

Impedance:

0 30 60 90 120150180210240270300330360390420450480510540

0.0

0.1

0.2

0.3

0.4

0.5

420 450 480

0.00

0.01

0.02

0.03 PZT

Z

T(oC)

% (5KHZ)

% (10KHZ) % (50KHZ)

% (100KHZ)

PZT

Z

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

0 70 140 210 280 350 420 490 560

0.00

0.02

0.04

0.06

0.08

0.10

0.12

350 420 490

0.00

0.02

PZT- 5%Sn

Z

T(oC)

% (5KHZ)

% (10KHZ) % (50KHZ) % (100KHZ)

PZT- 5%Sn

Z

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

0 70 140 210 280 350 420 490 560

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

350 420 490

0.00

0.01

0.02

0.03

0.04

PZT - Sn(10%)

Z

T(oC)

% (5KHZ)

% (10KHZ)

% (50KHZ)

% (100KHZ)

PZT - Sn(10%)

Z

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

Figure 4a to 4c: Impedance of spectra with temperature at various frequencies of Sn doped PZT

With increase in Sn4+ concentration impedance has been observed to increase, but the rate of decrease with

temperature is more dominant as can be observed from the figures 4a to 4c. This clearly shows that relaxation

phenomena due to grains are becoming more dominant with increase in tin concentration. The observed phase

transition temperatures (Tc) from the above graphs are shown in below table 4.

Table 4: Curie temperature

Samples Tc oC

Pb(Zr0.52Ti0.48)O3 435

Pb(Zr0.52Ti0.48)0.95 Sn0.05O3 350

Pb(Zr0.52Ti0.48)0.9 Sn0.1 O3 330

The decrease in transition temperature from ferroelectric state to paraelectric state with increase in Sn4+ content

implies that the material is more becoming like a relaxor. The high value of Curie temperature for undoped PZT

may be due to presence of PbO secondary phase as predicted from X-ray diffraction peaks.

Dielectric constant:

The dielectric analysis is an important characteristic that can be used to fetch knowledge based on the electrical

properties of a material medium as a function of temperature and frequency. Based on this analysis, the

capability of storing electric charges by the material and capability of transferring the electric charge can be

assessed. The dielectric constant is calculated using the formula

ε' = Ct/εoA

where

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C is capacitance (F), t the thickness (m), A the area (m2), and εo the absolute permittivity in the free space

having a value of 8.854 *10-12Fm-1.

The experiment was carried out from 50Hz to 5MHz for different temperatures varying from 30-500deg C. Fig.

show the variation of dielectric constant and dielectric loss with respect to various frequencies ranging from

5kHz to 100kHz.

0 100 200 300 400 500

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10 20 30 40 50 60 70 80 90 100 110 120

250

300

PZT

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ)

% (100KHZ)

PZT

T(oC)

% (5KHZ)

% (10KHZ) % (50KHZ) % (100KHZ)

0 50 100 150 200 250 300 350 400 450 500 550

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000PZT

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

0 50 100 150 200 250 300 350 400 450 500 550

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

15000

16000

17000

18000

PZT - Sn(10%)

T(oC)

% (5KHZ) % (10KHZ) % (50KHZ)

% (100KHZ)

Figure 5a to 5c: Variation of dielectric constant with temperature

Table 5: Curie temperature

Samples Tc oC

Pb(Zr0.52Ti0.48)O3 435

Pb(Zr0.52Ti0.48)0.95 Sn0.05O3 360

Pb(Zr0.52Ti0.48)0.9 Sn0.1 O3 325

It has been observed that the dielectric constant decreases with the increasing in frequency. The high value of

dielectric constant at low frequencies maybe due to the excitation of bound electrons, lattice vibrations, dipole

orientation and space polarizations. Non switching linear responses in the dielectric graphs are ascribed to space

charge polarization.

Then ε increases gradually and attains a maximum value atCurie Temperature. After Tcit decreases. The Tc

(Curie temperature) of pure PZT is 435oC which is seen from the dielectric constant temperature graph. But the

dielectric peaks are broadened and this may be due to the characteristic behavior of disordered perovskite

structure with diffuse phase transition. As frequency increases, the polarization with largerelaxation times cease

to respond and hence the decrease in dielectric constant. The change in dielectric constant with temperature can

be attributed to the fact that the orientation polarization is connected with thermal motion of molecules so

dipole cannot orient themselves at low temperatures.

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When the temperature is increased the orientation of the dipole is facilitated and thus increases the orientation

polarization which leads to increases of the dielectric constant with temperature. This indicates a phase

transition from ferroelectric to paraelectric phase atthat particular temperature called Curie temperature (Tc).

This broadening is due to the composition fluctuation or substitution disordering in the arrangement of cation

in one or more crystallographic sites in the structure leading to a microscopic heterogeneity in the composition

and thus in a distribution of different local Curie points. This also corresponds to the fact, that a

longrangeordered ferroelectric contains dipoles with the same “single” relaxation frequency,fr ≈ 106 Hz.

Dielectric loss:

The temperature dependence of tangent loss (tand) of PZT with selected frequencies (5kHz, 10kHz, 50kHz and

100kHz) is shown in Fig.---.

100 200 300 400 500

0

2

4

6

8PZT

tan

Temp(OC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

0 100 200 300 400 500

0

1

2

3

4

5PZT

tan

Temp(OC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

0 100 200 300 400 500

0

2

4

6PZT - Sn(10%)

tan

Temp(OC)

% (5KHZ) % (10KHZ) % (50KHZ) % (100KHZ)

Figures 6a to 6c: Variation of dielectric loss with temperature

It was observed that dielectric loss is constant upto transition temperature and then increases to a maximum

value due to space charge polarization and again decreases with increasing temperature. It show that the shape

of the ε peaks was broad, which is typical of a case diffuse transition with frequency dispersion. When the

measured frequency increased, the maximum of εmax was decreased and shifted to higher temperature while

dielectric loss increased near the Curie point, which is typical of a relaxor material.

CONCLUSION

Sn doped PZT was prepared by conventional solid state reaction method which exhibited

pervoskite structure of space group P4mm phase. From EDAX measurements the presence of stoichiometry in

these samples has been observed. Decrease in Curie temperature has been observed with increase in Sn

concentration from 435oC to 325oC.

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From impedance spectroscopy results reveal the conduction phenomena in Sn doped PZT is mainly due to

conduction within the grain. From loss tangent graph it is observed that tangent loss is constant up to transition

temperature and then increases to maximum value by reason of space polarisation.

REFERENCES

1. Shujun Zhang & Ru Xia & Thomas R. Shrout , J Electroceram (2007) 19:251–257

2. Tuan Ab Rashid et al, Fabrication of Lanthanum and Strontium Doped PZT Ceramics Using Solid State Reaction Method

10.4028/www.scientific.net/MSF.888.62

3. L. Lutterotti, M. Bortolotti, G. Ischia, I. Lonardelli and H.-R. Wenk, Rietveld texture analysis from diffraction images, Z.

Kristallogr., Suppl. 26, 125-130, 2007.

4. Crystallography Open Database code: 2107525

5. J. C. Wurst and J. A. Nelson, ‘Lineal Intercept Technique for Measuring Grain Size in Two‐Phase Polycrystalline Ceramics’

Journal of the American Ceramic Society, 55 (1972) 109-109.

6. C R M Wronski , “The size dependence of the melting point of small particles of tin”Br. J. Appl. Phys. 18 (1967) 1731

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