effect of sn doping at b-site on structural and electrical ... · effect of sn4+ doping at b-site...
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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: [email protected]
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.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
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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
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
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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.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
Page No:503
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
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
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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
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
Page No:505
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.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
Page No:506
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.
JASC: Journal of Applied Science and Computations
Volume 5, Issue 9, September/2018
ISSN NO: 1076-5131
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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
JASC: Journal of Applied Science and Computations
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ISSN NO: 1076-5131
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