07) 3352–3356www.elsevier.com/locate/matlet

Materials Letters 61 (20

Structural studies of BiFeO3 modified BMZ–PT ceramics

Seema Sharma a,⁎, D.A. Hall b, Preeti S. Mulage c

a Department of Physics, Birla Institute of Technology and Science, Goa Campus, Goa, Indiab School of Materials, Materials Science Center, University of Manchester, Manchester M1 7HS, UK

c Electrical and Electronics Engineering Department, Birla Institute of Technology and Science, Goa Campus, Goa, India

Received 21 June 2006; accepted 13 November 2006Available online 8 December 2006

Abstract

Bismuth perovskites have been attracting attention as a family of piezoelectric ceramics in place of the widely used Pb (Zr, Ti)O3 (PZT)system. The advantages of bismuth perovskites over PZT are environmentally more-friendly materials, a higher mechanical strength and Curietemperature. Most recently BiMgZrO3–PbTiO3 has been reported to be high temperature morphotropic phase boundary (MPB) piezoelectric withappreciably good ferroelectric and piezoelectric properties.

Bismuth containing crystalline solutions [(BiMgZrO3)1−y–(BiFeO3)y]x–(PbTiO3)1−x, (BMZ–BF–PT) have been synthesized by hightemperature solid-state reaction technique. The crystalline symmetry varied with the composition, indicating good solid-state solubility of BMZand BF with PT. X-ray diffraction (XRD) reveals that BMZ–BF–PT has a single-phase perovskite structure. The Morphotropic Phase Boundary(MPB) of BMZ–PT system lies in the region x=0.55 to x=0.6 which is supported by the transformation from tetragonal to rhombohedral phase.The SEM photographs reveal the uniform distribution of grains in the matrix. Variation of dielectric parameters with frequency (at roomtemperature) exhibit typical dielectric behavior for all compositions.© 2006 Elsevier B.V. All rights reserved.

Keywords: X-ray diffraction; Perovskite; Dielectric; Morphotropic Phase Boundary

1. Introduction

Piezoelectric ceramics based on the perovskite PZT systemare widely used as sensors and actuators. Traditional applica-tions of these materials include underwater sonar, ultrasoundtransducers and actuators. Advances in electronics andcomputer control have also led to the incorporation ofpiezoelectric materials into common devices and smart systems[1,2]. There are a number of piezoelectric sensors and devices inautomotive, aerospace and related industrial applications oftenin vibration sensing and/or canceling systems. Both theautomotive and aerospace industries have expressed the needfor actuation and sensing at higher temperatures than currentlyavailable. Specifically, under-hood automotive applicationssuch as internal vibration sensors, control surfaces, or activefuel injection nozzles require operation temperatures as high as

⁎ Corresponding author. Tel.: +91 832 2580311; fax: +91 832 5643017.E-mail address: seema_sharma26@yahoo.com (S. Sharma).

0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.matlet.2006.11.096

300 °C [3,4]. Commercially available piezoelectric materialsare generally limited to operating temperatures of one half TC orapproximately 150 °C for most PZT formulations.

Perovskite PZT has come to dominate the world market forpiezoelectric materials since its discovery in the mid-1950s. PZTbased materials take advantage of a nearly temperatureindependent compositional phase boundary (MPB) betweenrhombohedral and tetragonal phases. The existence of these twothermodynamically equivalent phases leads to production of ahighly domain oriented material during the required polingprocess, exhibiting enhanced dielectric and piezoelectric activity[1,5].

Recently new high temperature ferroelectric materials basedon (1−x) BiMeO3–x–PbTiO3 solid solutions (where Me3+=Sc,In, Fe, In, Yb, etc) have been identified [6–8]. Guided by aperovskite tolerance factor relationship with TC, low tolerancefactor BiMeO3 systems have projected transition temperaturegreater than PZT. Solid solution of BiMgZrO3–PbTiO3 (BMZ–PT) exhibits a stable perovskite structure. The objective of this

Fig. 1. XRD patterns of samples sintered at 1050 °C.

Fig. 2. XRD patterns of samples sintered at 1050 °C.

3353S. Sharma et al. / Materials Letters 61 (2007) 3352–3356

article is to interpret the structure–property relations in thepiezoelectric system [(1− x) BiMgZrO3–xPbTiO3 wherex=0.35 to 0.65]. In addition to this, the effect of the additionof BiFeO3 (BF) on structural properties of BMZ–PT binarysystem has been investigated in this paper.

2. Experimental

Polycrystalline samples of BMZ–PT designated as 35–65,40–60,45–55, 50–50 and BMZ–BF–PT (BMZ=40%, BF=0/25/50% and PT=60%) designated as 40–0–60, 40–25–60 and40–50–60, were prepared by high temperature solid-statereaction technique. PbO, MgO, TiO2, Bi2O3, Fe2O3 and ZrO2

(all Aldrich AR grade) were used as the starting materials.Stoichiometric weights of MgO, PbO, TiO2, Bi2O3, ZrO2 andFe2O3 were mixed and ball milled with distilled water for 48 h,using zirconia balls as the grinding media. After drying invacuum, calcination was carried out at 800 °C for 2 h in airfollowed by ball milling and drying. A single-phase formationwas confirmed by the X-ray diffraction (XRD) technique. Thecalcined powder was pressed at 100 MPa to form cylindricalpellets using a cold isostatic press (CIP). The pellets were thensintered at 1050 °C for 1.5 h. A PbO rich atmosphere wasmaintained by placing PbZrO3 powder in an alumina boat nearthe test samples in closed crucible configurations in order tominimize the lead loss during sintering.

X-ray diffraction (XRD) analysis was performed on a PW3710 Philips diffractometer using Cu Kα (λ=0.15405 nm)radiation in order to examine the phases present in the system.Differential Scanning Calorimetry (DSC) and Thermal Gravi-metric Analysis (TGA) studies were carried out from roomtemperature to 700 °C at a heating rate of 10°/min byNETZSCH (GMBH). STA449C software was used for theanalysis of these studies. Polished surface microstructure wasexamined by scanning electron microscopy (SEM) (XL30 FEG-Philips). Dielectric measurements were performed by HP4284A LCR meter. Relative dielectric permittivity (ε′) and

dielectric loss (ε″) were measured at the frequencies 0.1 KHz, 1,10 and 100 KHz at room temperature.

3. Results and discussion

3.1. XRD analysis

Fig. 1 shows the room temperature XRD patterns of BMZ–PT (35–65, 40–60, 45–55 and 50–50) samples sintered at 1050 °C. The peaksin the XRD patterns were found to be sharp with distinct diffractionpeaks.

This figure shows a structural transition from rhombohedral (45–55) to tetragonal (40–60), which is obvious from the splitting of (200)and (201) peaks.

The diffraction lines for the system BMZ–BF–PT Fig. 2 wereindexed in different crystal systems and unit cell configurations using acomputer programme package ‘POWDMULT’. Standard deviations,∑Δd=dobs− dcal where d is the inter-planar spacing, were found to beminimum for tetragonal structure. All XRDs of BMZ–BF–PT systemreveals a pure perovskite phase with tetragonal structure.

The unit cell parameters and the tetragonality for the system withdifferent BiFeO3 content is shown in Table 1.

Table 1Unit cell parameters

BMZ–BF–PT c/0A a/0A Tetragonality = c/a

40–0–60 2.0131 1.9954 1.017940–25–60 2.0479 1.9854 1.031440–50–60 2.0621 1.9724 1.0454

3354 S. Sharma et al. / Materials Letters 61 (2007) 3352–3356

The tetragonality is increasing with increase in BiFeO3 in thesample. There is a 1.35% increase in tetragonality from 40–0–60composition to 40–25–60 composition and another 1.34% increasefrom the 40–25–60 to 40–50–60 composition. This confirms thehardening effect of the inclusion of Fe content in the BMZ–PTsystem.

Fig. 3. a. DSC and TGA curves of 40–0–60 composition. b. DSC and TGAcurves of 40–25–60 composition. c. DSC and TGA curves of 40–50–60composition.

Fig. 4. a: 40–0–60, polished surface, backscattered electron image. b: 40–25–60, polished surface, backscattered electron image. c: 40–50–60, polishedsurface, backscattered electron image.

3.2. DSC and TG analysis

Panels a, b, and c of Fig. 3 show the typical curves for DSC andTGA measurements of 40–0–60, 40–25–60 and 40–50–60 composi-tions respectively.

3355S. Sharma et al. / Materials Letters 61 (2007) 3352–3356

It is inferred from the DSC curves of the sintered samples that thetemperature corresponding to the exothermic peak increases with theincrease in BiFeO3 content. This is expected also because the transitiontemperature of BiFeO3 is around 600 °C. From TGA curves, it is foundthat percentage loss in the mass is less than 0.08% for all the compositions.

3.3. SEM analysis

Panels a, b, and c of Fig. 4 show SEM photographs of 40–0–60,40–25–60 and 40–50–60 compositions respectively.

The black areas are pores and the thin white filaments are a liquidphase of PbO–Bi2O3 that appeared during sintering and is situated at

Fig. 5. a: EDAX spectrum of 40–0–60 sample. b: EDAX spectrum of 40–25–60sample. c: EDAX spectrum of 40–50–60 sample.

Fig. 6. a. Frequency dependence of ε′ for different compositions. b. Frequencydependence of ε″ for different compositions.

the grain boundary region. The liquid phase is in fact an amorphousphase resulting from sintering. The average grain size of all thecompositions was found to be in the range from 1.5 to 2 μm.

Fig. 5a, b, c shows the energy dispersive X-ray spectra of 40–0–60,40–25–60 and 40–50–60 samples.

These spectra show the different weight percent of the elementspresent in the system. It is seen that the peak corresponding to the Feelement increases with the increase in BF in the system.

3.4. Dielectric studies

Room temperature dielectric behavior of the compounds is shownin Fig. 6a and b. The curves for the frequency dependence of thedielectric permittivity (ε′) and dielectric loss (ε″) shows that thedielectric permittivity decreases with increase in frequency.

The fall in dielectric permittivity arises from the fact thatpolarization does not occur instantaneously with the application ofthe electric field because of inertia. The delay in response towards theimpressed alternating electric field leads to loss and decline in dielectricconstant [9]. At low frequencies, all the polarizations contribute. Asfrequency is increased, those with large relaxation times cease torespond and hence results in the decrease of the dielectric permittivity.The same type of frequency dependence is found in many ferroelectricceramics [10,11]. Room temperature variation of dielectric loss withfrequency (Fig. 5b) does not show an appreciable change.

4. Conclusions

A new high temperature solid–solution system BMZ–BF–PT has been investigated. Using conventional solid-stateprocessing techniques phase pure perovskite was achieved for

3356 S. Sharma et al. / Materials Letters 61 (2007) 3352–3356

all the compositions. At room temperature tetragonal phase wasidentified for all the compositions (BMZ–BF–PT) investigatedin the present study. SEM photographs reveal uniform grain sizedistribution in all the compositions. Room temperaturedielectric response exhibits the typical characteristics of adielectric material. This material is identified as a good low leadcontaining electroceramic with appreciable structural anddielectric properties.

Acknowledgements

The authors gratefully acknowledge the Royal Society,London, UK and Department of Science and Technology, Indiafor granting financial support through a visiting researchfellowship. One of authors, Dr. Seema Sharma acknowledgesDr. Rahul Mohan Gupta, Department of Ocean Development,Govt. of India for carrying out EDAX experiments.

References

[1] B. Jaffe, W.R. Cook, H. Jaffe, J. Piezoelectric Ceramics, Academic Press,New York, 1971.

[2] R.E. Newnham, in: N. Setter (Ed.), J. Ferroelectric Ceramics, 1992, p. 363.[3] R.C. Turner, P.A. Fuierer, R.E. Newnham, T.R. Shrout, J. Appl. Acoust. 41

(1994) 299.[4] M. Naito, Ceram. Eng. Sci. Proc. 8 (1987) 1106.[5] G.A. Smolenskii, in: G.W. Taylor (Ed.), J. Ferroelectrics and Related

Materials, 1984.[6] S. Zhang, D.Y. Jeong, Q. Zhang, T.R. Shrout, J. Cryst. Growth 247 (2003)

131.[7] R. Eitel, C.A. Randall, T.R. Shrout, S.E. Park, Jpn. J. Appl. Phys. 41

(2002) 2099.[8] R. Eitel, C.A. Randall, T.R. Shrout, P. Rehrig, W. Hackenberger, S.E. Park,

Jpn. J. Appl. Phys. 40 (2001) 5999.[9] S. Chopra, S. Sharma, T.C. Goel, R.G. Mendiratta, Solid State Commun.

127 (2003) 299.[10] J. Mal, R.N.P. Choudhary, Phase Transit. 62 (1997) 19.[11] N.K. Misra, R. Sati, R.N.P. Choudary, Mater. Lett. 24 (1995) 313.