PLEASE SCROLL DOWN FOR ARTICLE

This article was downloaded by: [PRAKASH, CHANDRA]On: 21 November 2010Access details: Access Details: [subscription number 929943759]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Integrated FerroelectricsPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713618055

Effects of Samarium Doping on the Ferroelectric Properties of ModifiedLead Zirconate Titanate CeramicsPratibha Singhab; Sangeeta Singha; J. K. Junejac; K. K. Rainab; R. P. Pantd; Chandra Prakashe

a Electroceramics Research Laboratory, Department of Physics, GVM Girls College, Sonepat, India b

School of Physics & Materials Science, Thapar University, Patiala, India c Department of Physics,Hindu College, Sonepat, India d National Physical Laboratory, New Delhi, India e Directorate ofER&IPR, New Delhi, India

Online publication date: 20 November 2010

To cite this Article Singh, Pratibha , Singh, Sangeeta , Juneja, J. K. , Raina, K. K. , Pant, R. P. and Prakash, Chandra(2010)'Effects of Samarium Doping on the Ferroelectric Properties of Modified Lead Zirconate Titanate Ceramics', IntegratedFerroelectrics, 122: 1, 23 — 30To link to this Article: DOI: 10.1080/10584587.2010.504139URL: http://dx.doi.org/10.1080/10584587.2010.504139

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.

Integrated Ferroelectrics, 122:23–30, 2010Copyright © Taylor & Francis Group, LLCISSN: 1058-4587 print / 1607-8489 onlineDOI: 10.1080/10584587.2010.504139

Effects of Samarium Doping on the FerroelectricProperties of Modified Lead Zirconate

Titanate Ceramics

PRATIBHA SINGH,1,3 SANGEETA SINGH,1 J. K. JUNEJA,2

K. K. RAINA,3 R. P. PANT,4 AND CHANDRA PRAKASH5,∗

1Electroceramics Research Laboratory, Department of Physics, GVM GirlsCollege, Sonepat-131001, India2Department of Physics, Hindu College, Sonepat-131001, India3School of Physics & Materials Science, Thapar University, Patiala-147004,India4National Physical Laboratory, New Delhi-110012, India5Directorate of ER&IPR, DRDO, DRDO Bhawan, New Delhi-110105, India

Polycrystalline ceramics samples having compositional formula PbZr0.588Ti0.392

Fe0.01Nb0.01O3 and Pb0.98Sm0.02Zr0.588Ti0.392Fe0.01Nb0.01O3 were prepared by traditionalsolid state route. Sintering was carried out at 1250◦C in closed alumina crucibles in leadrich atmosphere. XRD analysis confirmed formation of tetragonal perovskite structureand tetragonality was found to decrease with Sm substitution. In order to study mi-crostructure, SEM micrographs were recorded on freshly broken pieces. The grain sizewas observed to decrease with Sm addition. P-E hysteresis loops were recorded at dif-ferent temperatures for investigating ferroelectric properties. Sm substitution improvessquareness and remanence.

Keywords PZT; ferroelectrics; samarium

1. Introduction

Lead zirconate titanate, (Pb(Zrx,Ti1-x)O3, PZT) is one of the most common ferroelectricoxide in the perovskite ABO3 structure. It is considered an important material since longbecause of its high spontaneous polarization and Curie temperature well above room tem-perature. These features provide it thermal stability during operation, easier poling, higherelectromechanical coupling coefficient etc. The substitution of rare earth allows to modifyand especially to increase the performances of these materials in bulk form which furtherstrengthen the potential applications of PZT [1]. Generally, remnant polarization and the co-ercive field are used to characterize ferroelectrics while describing their dielectric propertiesinvestigated with the classic Sawyer and Tower circuit. These are important parameters forPZT to be employed for ferroelectric memory devices (FERAM). Concerning the effects ofdoping in PZT bulk forms on sintering temperature, permittivity, piezoelectric coefficientsand polarization, few works have already been published [2–8]. Structural and electrical

Received December 13, 2009; in final form May 3, 2010.∗Corresponding author. E-mail: cprakash@hqr.drdo.in

[1341]/23

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

24/[1342] P. Singh et al.

characterization of rare earth (La, Nd, Sm, Eu, Gd, Dy, Er and Yb) ion substituted PZTceramics emphasized the fact that fabricating only a pure single phase materials by sol-geltechnique may not necessarily give a high dielectric constant. Despite presence of poor py-rochlore phase in these materials, they exhibit excellent dielectric properties [9]. The effectsof donor dopants, particularly Sm, on the properties relative to dielectric & piezoelectricbehaviour have been discussed in many research papers [10–14]. We have recently reporteddielectric properties of Sm modified (Pb)(Zr,Ti,Fe,Nb)O3 ceramic system [15]. Here, weare reporting the ferroelectric properties of Sm-substituted modified PZT compositions,PSZFNT, having compositional formula Pb1-xSmxZr0.588Ti0.392Fe0.01Nb0.01O3 (where x =0 and 0.02).

2. Experimental Details

Samarium (Sm) substituted modified lead zirconate titanate (PSZFNT) polycrystallineceramics with general formula Pb1-xSmxZr0.588Ti0.392Fe0.01Nb0.01O3 (with x = 0 and 0.02)were prepared by conventional dry ceramic method by mixing the high-purity (99.9%)oxides (i.e. PbO, Sm2O3, ZrO2, TiO2, Fe2O3 and Nb2O5). Details of sample preparationare given in our earlier publication [15].

The structural studies of all the sintered samples were performed on D8 AdvanceX-ray diffractometer (manufactured by Bruker AXS) in a wide range of Bragg angles 2θ

(20◦ ≤ 2θ ≤ 70◦) with a scanning rate of 2o min−1. Microstructural analysis was carriedout on fractured surface of pellets using Scanning Electron microscope (SEM) JEOL JSM-6380. The sintered pellets were lapped using microgrit powder on a flat glass surface. Thesamples were ultrasonically cleaned and flat surfaces were electroded with silver paste forelectrical measurements. The P-E hysteresis measurements were taken in the temperaturerange 30–100◦C at operating frequency of 20 Hz using computer interfaced P-E loop tracerbased on modified Sawyer-Tower circuit.

3. Results and Discussion

3.1. XRD Analysis of PSZFNT

X-ray diffraction patterns of the PSZFNT specimens at room temperature are shown inFig. 1. The X-ray analysis indicates that the compounds possess tetragonal structure. WithSm substitution, the original peak position of the ingredient is shifting towards higher angleside indicating the decrease in tetragonality. However, a weak reflection peak is observedfor a 2θ value around 29◦ which is due to the presence of poor pyrochlore phase in thePSZFNT structure [16, 17]. It has been reported that in the formation of perovskite phasepyrochlore phase formation is an essential step [18]. This type of compound is consideredas oxygen deficient compound with a metastable transient phase [19]. It is found that XRDpattern of PZFNT is pyrochlore free, whereas for Samarium concentration i.e. for x =0.02 in PSZFNT, pyrochlore/metastable transient phase was seen whose percentage wasevaluated as 4% using the relation [20]

[Ipyro/(Ipyro + Iperov)] ∗ 100,

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

Samarium Doped Modified PZT Ceramics [1343]/25

20 30 40 50 60 70

(Pb1-x

SmxZr

0.588Ti

0.392Fe

0.01Nb

0.01O

3)

*

* = Pyrochlore phase

x=0.02

x=0

Inte

nsit

y (a

rb. u

nit)

2θ (degree)

Figure 1. XRD patterns of sintered PZFNT and PSZFNT specimens.

Figure 2. The scanning electron micrographs for the fractured surface of Pb1-xSmxZr0.588

Ti0.392Fe0.01Nb0.01O3 ceramics.

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

26/[1344] P. Singh et al.

which is negligibly small and hence the materials can be considered as single-phase [21,22]. The appearance of this extra phase may be attributed to Pb deficiency in the PSZFNTceramics.

3.2. SEM Analysis of PSZFNT

The microstructures of the sintered PSZFNT pellets for x = 0 and 0.02 are shown in Fig. 2.The SEM studies were done on freshly broken sintered pellets. It is found the grains ofdifferent sizes are uniformly and densely distributed over the entire surface. Absence ofthe pores shows good densification. For better understanding and estimation of grain sizeone can carry out SEM studies on highly polished and thermally etched samples. SEMstudies on samples sintered at different temperatures are also suggested to extend the workfurther. The average grain size of the samples, as determined by the linear intercept method,decreases with increase in Samarium doping.

-30 -20 -10 0 10 20 30

-20

0

20

x=0

Electric Field (kV/cm)

Pola

riza

tion

(µC

/cm

2 )

15 kV 20 kV 25 kV

-30 -20 -10 0 10 20 30

-40

-20

0

20

40x=0.02

Electric Field (kV/cm)

Pola

riza

tion

(µC

/cm

2 )

15 kV 20 kV 25 kV

Figure 3. Hysteresis loops of undoped and samarium doped PZFNT specimens.

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

Samarium Doped Modified PZT Ceramics [1345]/27

3.3. Ferroelectric Studies of PSZFNT

Typical polarization versus electric field (P-E) curves for Sm substituted PZFNT samplesare shown in Fig. 3. The samples show well-defined ferroelectric behaviour. The saturationand remnant polarizations (Pr and Ps) can be seen to increase with increase in electric field.A large increase in Pr is observed for sample with 2 mol% of Sm which is due to softeningeffect of Sm substitution, which also results in reduction in tetragonality. Sm doping isknown to relieve the stresses, which in turn increases both Pr and Ps [23]. The coercivefield (Ec) increases with increase in Sm. Such behaviour can be correlated with the averagegrain size variation, which exhibits the decrease in grain size for 2 mol% Sm (refer Fig. 2).It is reported in literature that as grain size decreases there is increase in Ec. This is due tothe fact that each grain is mechanically clamped by its surroundings. There are mechanicalstresses which accompany the 90o domain rotations. Both factors have a combined effectwhich tends to impede the polarization reversal process [24].

-30 -20 -10 0 10 20 30-40

-20

0

20

Electric Field (kV/cm)

Pola

riza

tion

(µC

/cm

2 )

x=0

30 oC

60 oC

90 oC

100oC

-30 -20 -10 0 10 20 30

-40

-20

0

20

40

Electric Field (kV/cm)

Pola

riza

tion

(µC

/cm

2 )

x=0.02

30 oC

60oC

90 oC

100oC

Figure 4. Hysteresis curves of Pb1-xSmxZr0.588Ti0.392Fe0.01Nb0.01O3 system with x = 0, 0.02 at 20Hz at different temperatures.

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

28/[1346] P. Singh et al.

Ferroelectric behaviour was also studied as a function of temperature. As temperatureis increasing, undoped PZFNT composition shows increase in Pr while sample with x =0.02 show decrease in Pr. This behavior is depicted in Fig. 4. This is due to the fact thatas temperature increases there is increase in thermal agitation of dipoles which result indecrease in remnant polarization. Variation of Pr and Ec with temperature is shown in Fig.5(a) and (b).

30 40 50 60 70 80 90 100

15

20

25

30

35

x=0.02

x=0

Pr (

µC/c

m2 )

Temperature ( oC)

30 40 50 60 70 80 90 100

6

7

8

x=0

x=0.02

Temperature (oC)

Ec (

kV/c

m)

Figure 5. Variation of Pr and Ec with temperature for undoped and samarium doped PZFNT speci-mens.

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

Samarium Doped Modified PZT Ceramics [1347]/29

4. Conclusions

In summary, PbZr0.588Ti0.392Fe0.01Nb0.01O3 (PZFNT) and Samarium substituted PZFNT(PSZFNT) ceramics were prepared by traditional solid-state process. The XRD patternsindicate tetragonal perovskite structure and polarization-hysteresis results indicate the fer-roelectric nature for the selected compositions. 2 mol% Sm substitution in undoped PZFNTcomposition enhanced the remnant polarization from 14.2 to 32.5 µC/cm2 and coercivefield from 7.3 to 7.7 kV/cm. The present study indicated that composition having 2 mol%Sm is a good memory type hysteresis loop. The measured ferroelectric properties of thesecompositions seem to be very promising for potential application in memory devices, ifthins films of these can be reproducibly made.

References

1. B. Jaffe, W. R. Cook, and H. Jaffe, Piezoelectric Ceramics. London: Academic Press; 1971.2. S. Sen, R. N. P. Choudhary, and P. Pramanik, Structural and electrical properties of Ca2+ modified

PZT electroceramics. Phys. B 387, 56–62 (2007).3. S. Dutta, R. N. P. Choudhary, and P. K. Sinha, Electrical properties of antimony doped PLZT

ceramics prepared by mixed-oxide route. J. Alloys Compds. 426, 345–351 (2006).4. B. Tang, H. Fan, S. Ke, and L. Liu, Microstructural evolutions and electrical properties of

Pb1-xLax(Zr0.56Ti0.44)1-x/4O3 ceramics. Mater. Sci. Eng. B. 138, 205–209 (2007).5. T. Hayashi, T. Inoue, and Y. Akiyama, Low-temperature sintering and properties of (Pb,Ba,Sr)(Zr,

Ti, Sb)O3 piezoelectric ceramics using uintering aids. Jpn. J. Appl. Phys. 38, 5549–5552 (1999).6. S. Y. Cheng, S. L. Fu, C. C. Wei, and G. M. Ke, The properties of low-temperature fired

piezoelectric ceramics. J. Mater. Sci. 21, 571–576 (1986).7. C. Galassi, E. Roncari, C. C. Capiani, and F. Cracium, Processing and characterization of high

Qm ferroelectric ceramics. J. Euro. Ceram. Soc. 19, 1237–1241 (1999).8. R. B. Atkin, and R. M. Fulrath, Point Defects and Sintering of Lead Zirconate-Titanate. J. Am.

Ceram. Soc. 54, 265–270 (1971).9. S. R. Shannigrahi, F. E. H.Tay, K. Yao, and R. N. P. Choudhary, Effect of rare earth (La, Nd,

Sm,Eu,Gd, Dy, Er and Yb) ion substitutions on the microstructural and electrical properties ofsol-Gel grown PZT ceramics. J. Euro. Ceram. Soc. 24, 163–170 (2004).

10. R. Ranjan, R. Kumar, B. Behera, and R. N. P. Choudhary, Effect of Sm on structural, dielectricand conductivity properties of PZT ceramics. Mater. Chem. Phys. 115, 473–477 (2009).

11. C. Prakash and J. K. Juneja, Investigations on Sm- and Nb-substituted PZT ceramics. Mod. Phys.Lett. B. 20, 1879–1882 (2006).

12. C. Prakash, and O. P. Thakur, Effects of samarium modification on the structural and dielectricproperties of PLZT ceramics. Mater. Lett. 57, 2310–2314 (2003).

13. S. R. Shannigrahi, and R. N. P. Choudhary, Structural and electrical properties of sol-gel preparedSm modified Pb(Zr0·60Ti0·40)O3 ceramics: British Ceramic Transactions. 101, 25–29 (2002).

14. C. Pramila, T. C. Goel, and P. K. C. Pillai, Investigations on the piezoelectric and structuralproperties of samarium-doped lead zirconate titanate ceramics. Mater. Sci. Eng. B; 26, 25–28(1994).

15. P. Singh, S. Singh, J. K. Juneja, C. Prakash, and K. K. Raina, Dielectric studies of Samariummodified (Pb)(Zr, Ti, Fe, Nb)O3 ceramic system. Mod. Phys. Lett. B. 23, 1437–1442 (2009).

16. J. Lian, L. Wang, J. Chen, K. Sun, R. C. Ewing, J. M. Farmer, and L. A. Boatner, Theorder–disorder transition in ion-irradiated pyrochlore. Acta Mater. 51, 1493–1502 (2003).

17. S. R. Shannigrahi, R. N. P. Choudhary, and H. N. Acharaya, X-ray, SEM and dielectric studiesof Gd-modified sol–gel-prepared lead zirconate–lead titanate solid solution. Mater. Lett. 39,318–323 (1999).

18. A. H. Carim, B. A. Tuttle, D. H. Doughty, and S. L. Martinez, Microstructure of solution-processed lead zirconate titanate (PZT) thin films. J. Am. Ceram. Soc. 74, 1455–1458 (1991).

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010

30/[1348] P. Singh et al.

19. K. G. Brooks, I. M. Reaney, R. Klissurska, Y. Haung, L. Bursill, and N. Setter, Orientation ofrapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates. J. Mater. Res.9, 2540–2553 (1994).

20. S. L. Swartz, and T. R. Shrout, Fabrication of perovskite lead magnesium niobate. Mater. Res.Bull. 17, 1245–1250 (1982).

21. A. Govindan, H. D. Sharma, A. K. Tripathi, P. K. C. Pillai, and T. C. Goel, Studies on the dielectric,piezoelectric, pyroelectric and structural properties of Pb1-xGdx(Zr0.60Ti0.40)O3. Ferroelectrics134, 217–222 (1992).

22. S. R. Shannigrahi, R. N. P. Choudhary, and H. N. Acharya, Structural and dielectric propertiesof Nd modified Pb(Zr0.60Ti0.40)O3 ceramics. Mater. Sci. Eng. B. 60, 31–39 (1999).

23. X. Dai, Z. Xu, J. F. Li, and D. Viehland, Effects of lanthanum modification on rhombohedralPb(Zr1−xTix)O3 ceramics. I. Transformation from normal to relaxor ferroelectric behaviors. J.Mater. Res. 11, 618–625 (1996).

24. K. Carl, Ferroelectric properties and fatiguing effects of modified PbTiO3 ceramics. Ferroelectrics9, 23–32 (1975)

Downloaded By: [PRAKASH, CHANDRA] At: 17:00 21 November 2010