IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS

J. Phys. D: Appl. Phys. 40 (2007) 7565–7571 doi:10.1088/0022-3727/40/23/049

Internal friction andlongitudinal modulus behaviour ofmultiferroic PbZr0.52Ti0.48O3+Ni0.93Co0.02Mn0.05Fe1.95O4−δ

particulate compositesM Venkata Ramana1, G Sreenivasulu2, N Ramamanohar Reddy1,K V Siva Kumar1, B S Murty2 and V R K Murthy3

1 Ceramic Composite Materials Laboratory, Department of Physics,Sri Krishnadevaraya University, Anantapur–515 003, India2 Nanotechnology Laboratory, Department of Metallurgical and Materials Engineering, IndianInstitute of Technology, Chennai–600 036, India3 Microwave Laboratory, Department of Physics, Indian Institute of Technology,Chennai-600 036, India

E-mail: sivakumar.sivani@gmail.com

Received 30 August 2007, in final form 5 October 2007Published 16 November 2007Online at stacks.iop.org/JPhysD/40/7565

AbstractMultiferroic particulate composites with compositionxNi0.93Co0.02Mn0.5Fe1.95O4−δ + (1 − x)PbZr0.52Ti0.48O3 where the molarfraction x varies as 0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by theconventional ceramic method. The presence of two phases was confirmed byx-ray diffraction and scanning electron microscopy. The temperature variationof the longitudinal modulus (L) and the internal friction (Q−1) of theseparticulate composites at 104.387 kHz was studied in the wide temperaturerange 30–420 ◦C. The temperature variation of the longitudinal modulus (L) ineach composition of these particulate composites showed two abrupt minima.One minimum coincided with the ferroelectric–paraelectric Curie transitiontemperature (θE) and the other with the ferrimagnetic–paramagnetic Curietransition (θM ) temperature. The internal friction (Q−1) measurements alsoshowed two sharp peaks in each composition corresponding to thosetemperatures where the minima were noticed in the temperature variation of thelongitudinal modulus behaviour. The Curie transition temperature of pure ferritewas found to be 560 ◦C. Addition of 10% of ferrite to ferroelectric in amagnetoelectric (ME) composite resulted in a 360 ◦C fall in θM and with afurther increase in ferrite content the θM variation was found to be very nominal.However, no significant ferroelectric Curie transition temperature shift could benoticed. This behaviour is explained in the light of structural phase transitions inthese multiferroic particulate composites. These ME composites were preparedwith a view to using them as ME sensors and transducers.

1. Introduction

Composite materials consisting of piezoelectric andpiezomagnetic phases show a magnetoelectric (ME) effect.The ME effect is a coupled, two field effect, in which

the application of electric field induces magnetization andthe magnetic field produces an electric polarization. TheME effect is a property of the composites which is absentin their constituent phases [1]. When a magnetic field isapplied to an ME composite containing both piezoelectric and

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piezomagnetic phases, the ferrite particles experience a straindue to magnetostriction, and this strain is communicated tothe piezoelectric particles, resulting in the development ofpiezo-voltage (ME voltage) [2]. Such multiferroic compos-ites are highly useful as Hall sensors, waveguides, modulators,switches, phase inverters, rectifiers, etc [3]. Though these com-posites find a lot of technical importance in radioelectronics,optoelectronics, microwave electronics and transducers ininstrumentation, the literature survey indicates that not muchextensive work on various properties has been done on thesecomposites. The work is mostly confined to the measurementof the ME effect in composites containing a ferroelectric mate-rial as the first component such as BT, PZT, PMN-PT, PZN-PTand Ni [4–6] and Co [7–9], Ni–Co–Mn [10], Ni–Co–Cu–Mnferrite [11], Cu [12, 13] ferrite as the second component. Thedata available in the literature on the investigation of proper-ties such as elastic, anelastic, piezoelectric and magnetostric-tive nature on these ME particulate composites are scanty.As reported by many workers [14–16] and from our ownobservations [17, 18], elastic modulus and internal frictionmeasurements are very sensitive tools for identifing the phasetransitions, since they are lattice-related properties. Hence inthis work, a highly piezoelectric material such as lead zirconatetitanate, PbZr0.52Ti0.48O3 (PZT), was chosen as a ferroelectriccomponent, because of its excellent dielectric, pyroelec-tric and piezoelectric properties. Similarly, a highly mag-netostrictive material such as Ni0.93Co0.02Mn00.5Fe1.95O4−δ

(NCMF) was chosen as the piezomagnetic component. NCMFis generally used in ultrasonic applications such as radia-tors and hydrophones [19, 20]. The temperature variationof the elastic behaviour (L) and internal friction (Q−1) ofxNi0.93Co0.02Mn00.5Fe1.95O4−δ +(1−x)PbZr0.52Ti0.48O3 (x =0, 0.1, 0.2, 0.3, 0.4 and 0.5 mole fraction) multiferroic partic-ulate composites were studied in the wide temperature range30–420 ◦C. The results are reported in this paper and they arediscussed in the light of structural phase transitions.

2. Experimental details

2.1. Preparation of ferrimagnetic phaseNi0.93Co0.02Mn0.05Fe1.95O4−δ (NCMF)

The piezomagnetic phase (Ni0.93Co0.02Mn0.05Fe1.95O4−δ) wasprepared by using the analytical grade NiO (97%), CoO (99%),MnO2 (98%) and Fe2O3(99.9%). Stoichiometric amounts ofthese oxides were weighed and mixed thoroughly. Theseconstituents were ball-milled (RETSCH PM–200, Germany)in agate bowls with agate balls in an ethyl alcohol mediumfor 20 h. The slurry was dried and the dried powders wereloosely packed in the form of cakes. These cakes werecalcined in closed alumina crucibles at 800 ◦C for 2 h. Aftercalcination, these cakes were crushed and powdered. Thesepowders were ball-milled once again under the same conditionsin ethyl alcohol medium for 8 more hours to obtain a fineparticle size.

2.2. Preparation of ferroelectric phasePbZr0.52Ti0.48O3 (PZT)

The piezoelectric phase Pb(Zr0.52Ti0.48)O3 was prepared fromthe starting materials such as the analytical grade PbO (98%),

ZrO2 (99%) and TiO2(99%). These constituents were weighedin stoichiometric proportion and mixed thoroughly. Thismixture was ball-milled (RETSCH PM–200, Germany) intungsten carbide bowls with tungsten carbide balls in ethylalcohol medium for 20 h. The slurry was dried and the driedpowders were loosely packed in the form of cakes and thencalcined in closed alumina crucibles at 700 ◦ C for 2 h. Aftercalcination, these cakes were crushed and powdered. Thesepowders were ball-milled once again under similar conditionsin ethyl alcohol medium for 8 more hours to obtain a fineparticle size. Both ferrite and ferroelectric green powderswere sieved to obtain a uniform particle size. These fine greenpowders thus obtained were employed for the preparation ofthe composites.

2.3. Preparation of particulate composites

Employing these ferroelectric and ferrite green pow-ders, ME particulate composites with a generic formulaxNi0.93Co0.02Mn00.5Fe1.95O4−δ + (1 − x)PbZr0.52Ti0.48O3

(x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 mole fraction) were pre-pared. These powders were ball-milled (RETSCH PM 200,Germany) using high purity tungsten carbide balls in tungstencarbide bowls in ethyl alcohol for 3 h. The slurry obtainedwas dried and used for the preparation of samples of the de-sired shapes. The powders were mixed with 2% polyvinylalcohol as binder and pressed into bars of square cross section3.5 × 10−3 m × 3.5 × 10−3 m and 2.05 × 10−2 m long using ahydraulic press. These bars were finally sintered at 1130 ◦C for2 h in a programmable furnace (INDFUR, India) with a PZTatmosphere powder bed and were cooled to room temperatureat the rate of 80 ◦C h−1.

The experimental technique employed in this work forthe measurement of internal friction (Q−1) and longitudinalmodulus (L) behaviour is the composite resonator technique[21] with a few modifications [22]. By determining theresonant frequency fs of the composite system and logarithmicdecrement δ, the internal friction (Q−1) and the longitudinalmodulus (L) were evaluated using the standard relations[17,23]. Q−1 and L data obtained in the present investigationare accurate to 5% and 2%, respectively.

The x-cut quartz transducer used in the presentinvestigation has a length of 2.653 × 10−2 m, width of3.32 × 10−3 m, natural frequency 104.387 kHz and a massof 1.0316 × 10−3 kg. The electrode faces were painted withconducting silver paint (Du Pont). The composite oscillatorwas formed by cementing the quartz transducer to the specimenof identical cross-section. The adhesive used in this work wasa paste containing one part by weight of calcium carbonate andfive parts by weight of sodium metasilicate in a small quantityof distilled water. The composite system works satisfactorilyafter it has been kept for 24 h at room temperature.

In order to study the effect of temperature on internalfriction and longitudinal modulus of the multiferroic compositespecimens, the composite resonator system with the sampleholder was placed at the centre of a tubular electric furnace.The details of the furnace and temperature controller assemblywere described elsewhere [18]. All the internal frictionmeasurements were performed with a strain amplitude of 10−6,after the specimen had attained thermal equilibrium.

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Figure 1. XRD patterns of the ME composites with x = 0.1, 0.3and 0.5.

2.4. Characterization

The x-ray diffractograms were obtained using the XRD system(PM 1730, Germany) using Cu Kα radiation. The specimenswere polished with 0.3 µm alumina polishing powder andwere thermally etched prior to the examination with scanningelectron microscope (SEM, FEI QUANTA 200, Japan).

3. Results and discussion

Figure 1 shows the XRD patterns of the particulate compositesof x = 0.1, 0.3 and 0.5, respectively. All the XRD peaks couldbe identified for both the perovskite and the spinel phases.All the patterns were almost similar to each other exceptfor the intensity of the peaks. An examination of the figureshows that the diffraction patterns contain both ferroelectricand ferrite peaks. It can be seen from the figure that theintensity of the ferrite peaks increases with the increase inthe ferrite composition. However, the intensity of the peakscorresponding to the ferroelectric phase decreases with theincrease in the ferrite concentration.

Figure 2 shows the typical scanning electron microscopy(SEM) patterns of the particulate composites of x = 0.1, 0.3and 0.5, respectively.

3.1. Longitudinal modulus measurements

The temperature variation of the longitudinal modulus, L,and the internal friction, (Q−1), for various samples ofxNi0.93Co0.02Mn00.5Fe1.95O4−δ+(1−x) PbZr0.52Ti0.48O3 (x =0, 0.1, 0.2, 0.3, 0.4 and 0.5) are shown in figures 3 and 4,respectively. An examination of the data presented in figure 3shows that there is a systematic variation of the longitudinalmodulus (L) as a function of temperature.

In pure PZT (figure 3(a)), the ferroelectric–paraelectricphase transition at 390 ◦C can be very clearly seen as a sharp fallin the modulus at the ferroelectric Curie transition temperature(θE) [24, 26]. This type of sharp kink in the modulus wasreported by Dai et al [14], Jamenez and Vincent [15] andBourim and Tanaka [16] in pure PZT. In addition to this kink at390 ◦C, a broad minimum can be noticed at 230 ◦C. A similartype of behaviour was also noticed by Dai et al [14] in purePZT. This was attributed to the movement of domain walls andpoint defects in the sample.

Figure 2. Typical SEM photographs of the ME composites with(a) x = 0.1, (b) x = 0.3 and (c) x = 0.5.

An examination of figure 3(b), for the ME particulatecomposite with x = 0.1, reveals that the temperature variationof the longitudinal modulus (L) shows a flat response overa wide temperature range and shows a sharp minimum at380 ◦C. This temperature coincides with the ferroelectricto paraelectric phase transition of the ferroelectric phasein the composite which is characterized by θE . However,no anomalous variation in longitudinal modulus could beobserved around 230 ◦C unlike in pure the PZT sample [25].

Figures 3(c)–(f ) show the temperature variation of thelongitudinal modulus (L) in ME particulate compositeswith x = 0.2, 0.3, 0.4 and 0.5, respectively. Thesefigures show two sharp minima ‘A’ and ‘B’ in eachcase, unambiguously indicating two phase transitions. Theminimum ‘A’ obtained around 390 ◦C coincides with theferroelectric–paraelectric phase transition at the ferroelectricCurie transition temperature [26]. However, the positionof second minimum ‘B’ was obtained around 200 ◦C in thecomposites studied in this work. This type of sharp fall in

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(°C) (°C)

(°C)(°C)

(°C) (°C)

Figure 3. Temperature variation of the longitudinal modulus, L, of pure PZT (a) and of ME composites with (b) x = 0.1, (c) x = 0.2,(d) x = 0.3, (e) x = 0.4 and (f ) x = 0.5.

modulus and the sharp peak in internal friction was reportedby Koster and Bangert [27] in Hume-Rothery alloys in theneighbourhood of solidus temperature. In order to confirm thisphase transition, the ferrimagnetic Curie transition temperature(θM ) was studied in these composites using the techniqueemployed by Loria and Sinha with a few modifications [28].The minimum ‘B’ obtained in the temperature variationof longitudinal modulus plots in each composite coincideswith the corresponding ferrimagnetic–paramagnetic phasetransition temperature (θM ) of that ME composite.

3.2. Internal friction measurements

Figure 4(a) represents the temperature variation of the internalfriction (Q−1) in pure PZT. The internal friction loss shows a

sharp peak corresponding to the ferroelectric Curie transitiontemperature (θE) at 390 ◦C. In addition to this, one can noticea small but distinct peak at around 230 ◦C correspondingto the minimum obtained in the longitudinal modulus (L)behaviour with the temperature of pure PZT. As explainedearlier, Jamenez and Vincent [15] and Bourim and Tanaka [16]have attributed the minor peak to the domain wall motion andpoint defects in the sample.

Figure 4(b) shows the temperature variation of the internalfriction in the ME particulate composite with x = 0.1, whereonly one sharp peak can be noticed at the ferroelectric Curietransition temperature θE .

However, in the case of composites with x = 0.2,0.3, 0.4 and 0.5, respectively, (figures 4(c)–(f )) we can findtwo sharp peaks ‘A’ and ‘B’ at two different temperatures.

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(°C) (°C)

(°C)(°C)

(°C) (°C)

Figure 4. Temperature variation of the internal friction (Q−1) of pure PZT (a) and ME composites with (b) x = 0.1, (c) x = 0.2,(d) x = 0.3, (e) x = 0.4 and (f ) x = 0.5.

The sharp peak ‘A’ obtained around 390 ◦C coincides withthe ferroelectric–paraelectric phase transition temperaturecharacterized by θE [24]. The sharp peak ‘B’ obtainedin the temperature variation of anelastic behaviour ofthese multiferroic particulate composites (figures 4(c)–(f ))coincides with the ferrimagnetic Curie transition temperature(θM ) characteristic of the magnetic component of the MEcomposites. Generally in ferroic materials, the density ofthe domain walls increases when the temperature approachesthe Curie transition temperature. With the increase intemperature the increase in mobility and density of domainwalls result in an increase in the internal friction. If thedensity of the domain walls is so large, such that theinteraction of domain walls affects the mobility of domainwalls, the internal friction decreases. These two opposing

tendencies lead to the formation of an internal frictionpeak [29].

The Curie transition temperature, θM , of pure NCMFwas found to be 560 ◦C. The variation of the ferrimagnetic–paramagnetic phase transition temperature of the ferritecomponent in the composites with increasing mole fractionof the ferrite component is shown in figure 5. It can be noticedthat the addition of 10% of ferrite to ferroelectric resulted ina 360 ◦C fall in θM and with the further increase in the ferritecontent the θM variation is found to be very nominal. Thesecond peak ‘B’ in the ME composite with x = 0.1 is notperceptible due to low ferrite content present in the composite.

In the absence of any phase transition, generally, in solidsthe elastic modulus decreases with the increase in temperature.However, in the present investigation, the composites studied

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Figure 5. Variation of θM with the mole fraction of ferrite.

contain both ferroelectric (PZT) and ferrimagnetic (NCMF)phases. In the temperature range studied, i.e. 30–420 ◦C,the pure ferroelectric component, PbZr0.52Ti0.48O3, transformsfrom ferroelectric to the non-ferroelectric phase at 390 ◦C.Hence, there should be anomalous behaviour in both elasticand anelastic properties near the phase transition, because theseare lattice-related properties. In the temperature variation ofthe longitudinal modulus L, of pure PZT and its composites,this behaviour is depicted (figure 3) in this work. Thepeaks observed in figures 4(a)–(f ) also confirm this phasetransition θE . Similarly an examination of figures 3 and 4reveals that there is another transition due to ferrimagneticto paramagnetic transformation at the ferrimagnetic Curietransition temperature θM . It appears that in the loweringof θM with the ferrite content in these composites indicatesthat the presence of the ferroelectric perovskite phase affectsthe ferrimagnetic spinel structure appreciably. However,the ferroelectric Curie transition temperature (θE) is notmuch affected by the presence of spinel ferrite phase in thecomposites, because the shift in θE is not appreciable.

In principle, the ME composites should show two Curietransition temperatures, namely, one due to ferrimagnetic–paramagnetic phase transition (θM ) and the other due toferroelectric–paraelectric phase transition (θE). In ourprevious studies on the dielectric behaviour of these particulatecomposites [26], we could identify the ferroelectric–paraelectric phase transition only. In this work on thetemperature variation of elastic and anelastic behaviour of themultiferroic particulate composites both θE and θM could beidentified unambiguously since these properties are lattice-related properties.

4. Conclusions

The studies on the temperature variation of elastic andanelastic behaviour of ME particulate composites containingpiezoelectric (PZT) and piezomagnetic (NCMF) phases throwconsiderable light on the phase transitions present in thesecomposites, since they are lattice-related properties. The XRDanalysis of the particulate ME composites studied in this workreveals that the composites contain a ferroelectric componentwith perovskite structure and a ferrite component with spinelstructure. The temperature variation of the longitudinalmodulus (L) study shows two sharp minima correspondingto ferroelectric and ferrimagnetic Curie transition temperatures

θE and θM , respectively, in all the composites except in the caseof the composite with x = 0.1. The temperature variation ofthe internal friction (Q−1) exhibits two peaks correspondingto the two minima obtained in the temperature variation of thelongitudinal modulus (L). There is no noticeable effect of theferrite phase on the ferroelectric phase. However, the effect ofthe ferroelectric phase on the ferrite phase is quite noticeable.In order to study the ferroelectric and ferrimagnetic domaininteraction in these composites, the work on the effect of themagnetic field on these phase transitions is in progress.

Acknowledgments

The authors thank Professor A Varada Rajulu, Department ofPolymer Science and Technology, S K University, Anantapur,for the encouragement given during the progress of thiswork and for his useful discussions on the preparation ofthe manuscript. This work is supported by the financialassistance provided by Defence Research and DevelopmentOrganization (DRDO), New Delhi, India, by the grantNo ERIP/ER/0303437/M/01/761. One of the authorsM Venkata Ramana, would like to thank DRDO, New Delhi,for providing a Senior Research Fellowship.

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