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Materials Chemistry and Physics 105 (2007) 273–277

Single-crystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3/epoxy 1–3 piezoelectriccomposites prepared by the lamination technique

Feifei Wang a,b,∗, Chongjun He a,b, Yanxue Tang a,b, Xiangyong Zhao a, Haosu Luo a

a The State Key Laboratory of High Performance Ceramics and Superfine Microstructure,Shanghai Institute of Ceramics, Chinese Academy of Sciences, 215 Chengbei Road, Jiading, Shanghai 201800, China

b Graduate School of the Chinese Academy of Sciences, Beijing 100049, China

Received 25 October 2006; received in revised form 18 April 2007; accepted 26 April 2007

bstract

In present work, 〈0 0 1〉-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMNT30%)/epoxy 1–3 piezoelectric composites withb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) volume fraction ranging from 0.25 to 0.7 were prepared using the lamination technique. Compared

o the dice and fill method which is commonly adopted, this technique makes full use of the size of as-grown PMNT single crystal to fabricateiezoelectric composites with larger dimensions, and greatly reduces the damage to PMNT single crystal as well. Results show that preparedMNT30%/epoxy 1–3 piezoelectric composites, as well as the composites prepared by dice and fill method, own superior piezoelectric

roperties to PMNT single crystal with higher thickness electromechanical coupling coefficient kt, moderate relative dielectric constant εr andomparatively low acoustic impedance Z. These make the PMNT30%/epoxy 1–3 piezoelectric composites become a potential in ultrasonicransducer applications. 2007 Elsevier B.V. All rights reserved.

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eywords: Composite materials; Piezoelectricity; Electrical properties

. Introduction

〈0 0 1〉-Oriented relaxor-based ferroelectric single crystalb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) has been reported toossess ultrahigh piezoelectric response (longitudinal elec-romechanical coupling coefficient k33 ∼ 94%, piezoelectrictrain constant d33 ∼ 2500 pC/N) [1–3] near the morphotropichase boundary region and provides a higher sensitivity androader bandwidth [4–6] than those of traditional piezoelectriceramics when applied in the ultrasonic transducers. However,igh acoustic impedance of PMNT single crystal is hard toatch with the human issue and water well, furthermore, the

hickness electromechanical coupling coefficient kt of PMNT

ingle crystal is relatively low (about 0.6), which is often uti-ized. These restrict the converting efficiency from electricalo acoustic energy. Previous investigations indicated that 1–3

∗ Corresponding author at: The State Key Laboratory of High Performanceeramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinesecademy of Sciences, 215 Chengbei Road, Jiading, Shanghai 201800, China.el.: +86 21 6998 7759; fax: +86 21 5992 7184.

E-mail address: f f w@sohu.com (F. Wang).

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254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2007.04.060

iezoelectric composites could effectively combine the desiredroperties of a piezoelectric material and a polymer, improve kt,nd adjust the impedance close to human issue and water [7–9].

Experiences tell us that when the piezoelectric compositesre fabricated, the techniques have significant influences on theltimate composite material properties. Currently the dice andll method [10] may be the most widespread fabrication methodor composites [11]. When it was used to fabricate the single-rystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMNT30%)/epoxy–3 composites, we found that two dimension sizes of PMNTingle crystal would be considered in the (0 0 1) plane, so thevailable size was comparatively small. Furthermore, as a resultf the small dicing gap, the crystal may break very easily duringhe twice dicing, which may waste a large amount of crystals.n order to fabricate piezoelectric composites with larger size toeet the underwater transducer applications, reduce the damage

o PMNT single crystal, a lamination technique was adopted ashown in Fig. 1 [12,13]. Using this technique, we only need

o consider one dimension size of PMNT single crystal in the0 0 1) plane, so larger composites can be prepared. Besides,he damage to PMNT single crystal was greatly reduced and noragmentation would happen. A long composites pillar could be

274 F. Wang et al. / Materials Chemistry and Physics 105 (2007) 273–277

Fig. 1. Lamination technique for composites fabrication [13]. The black and thewhite plates represent PMNT and epoxy resin, respectively. Alternate plates ofPts

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MNT and epoxy resin are glued together to form a layered structure. Slices ofhe layered structure are again alternated with epoxy resin and glued into a finaltructure.

repared once from which 1–3 plates with different thickness cane sliced at one time, which is very suitable for mass-productionompared to the dice and fill method. This method would belso very effective for fabricating PZT/epoxy 1–3 piezoelectricomposites.

. Experimental

PMNT30% single crystal was grown by a modified Bridgman method [14]nd oriented along the [0 0 1] direction using the X-ray diffractometer. Perpen-icular to the (0 0 1) plane, PMNT plates with different thickness (referred to theMNT rod width, as shown in Table 1) were cut and the main surface dimensionsf the plates were 7.6 mm × 7.6 mm. The rapid epoxy adhesive with a hardenerin 4:1 ratio, Araldite, Huntsman Company) was cured at 45 ◦C for about 48 hntil it was solidified completely, and then it was cut into the same dimensionsith PMNT in the main surface with 0.3 mm thick. After that PMNT plates and

poxy resin were alternately bonded together to form a laminated block usinghe same epoxy as the bonding agent, which was then cut to form a plurality ofaminated plates. The laminated plates were then laminated with epoxy platesgain to form the composites. Subsequently, the composites with different thick-

ess could be cut. As a result of the thickness of epoxy as the bonding agent wasery thin, when calculating the volume fraction of PMNT, it was not considered.o the calculated volume fraction of PMNT shown in the figures may be a littleigher.

wo

able 1s-prepared four samples with different fractions of single-crystal PMNT/epoxy 1–3

ample number Thickness, t (mm) Width of PMNT rod, a (mm)

# 3 0.3# 3 0.42# 2.5 0.9# 3 1.5

ig. 2. Impedance and phase angle vs. frequency spectrum of PMNT30%/epoxy–3 piezoelectric composites with a 0.56 volume fraction of PMNT singlerystal.

The obtained samples with different volume fractions were flattedith a machine and painted with silver electrodes at room temperature.MNT30%/epoxy 1–3 piezoelectric composites were poled in silicon oil undern electric field of 1.5 kV/mm at room temperature for 15 min. During the fabri-ation process, make sure that the ultimate attained main surface must be (0 0 1)lane. Impedance spectrums of the samples were obtained at room temperaturesing an Agilent4285A impedance analyzer. Relative dielectric constant εr atkHz was measured using HP4194A impedance analyzer at room temperature.iezoelectric constant d33 was measured by a ZJ-3A d33 meter at 55 Hz.

. Results and discussion

As-prepared PMNT30%/epoxy 1–3 piezoelectric compositesn the present work have been laminated very well, so they cane considered as an integrated material. Table 1 shows the densi-ies and the dimensions of the composites with different volumeractions of PMNT single crystal. Over the range of volume frac-ion from 0.25 to 0.7, the density varies from 2.33 to 4.93 g/cm3.or the density of PMNT single crystal is much larger than thatf epoxy resin, the density increase linearly with the increase ofhe PMNT volume fraction.

Fig. 2 shows the impedance and phase angle versus frequencyf PMNT30%/epoxy 1–3 piezoelectric composites with a 0.56olume fraction of PMNT. Following the IEEE standard oniezoelectricity [15], electromechanical properties of the com-osites were characterized. kt can be determined according tohe impedance spectrum by the following formula:

2 π fs(

π fp − fs)

t 2 fp 2 fp

here fs and fp represent the resonant and antiresonant frequencyf the piezoelectric composites, respectively, corresponding to

piezoelectric composites

Width of epoxy, b (mm) PMNT volume fraction Density (g/cm3)

0.3 0.25 2.330.3 0.34 2.740.3 0.56 4.310.3 0.7 4.93

F. Wang et al. / Materials Chemistry and Physics 105 (2007) 273–277 275

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Fig. 5. Piezoelectric constant d33 as a function of PMNT volume fraction.

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ig. 3. Thickness electromechanical coupling coefficient kt as a function ofMNT volume fraction.

he minimum and maximum of the impedance. According tohe impedance spectrum, the calculated kt is 0.80, as is shownn Fig. 3, which is much higher than that of PMNT single crys-al (about 0.6), but still lower than k33 of PMNT single crystal>0.9). Improved kt attributes to the epoxy which restrict cer-ain lateral vibration of PMNT rods and modify their behaviors free rods, therefore, high thickness/width ratio is obtained,hich makes the rod approximately exhibit longitudinal vibra-

ion mode. If more compliant epoxy resin was used, kt may beigher. From Fig. 3, we can also see that when the volume frac-ion exceeds a certain range, kt decrease instead. This indicateshat kt strongly depend on the volume fraction of piezoelec-ric materials. During the practical application, proper volumeraction should be selected.

Fig. 4 shows elastic stiffness constant CD33 varies with differ-

nt volume fraction. CD33 was determined by

D33 = ρ(2tfp)2 (2)

here ρ, t, fp represent the density, thickness, antiresonantrequency of the sample, respectively. CD

33 increases linearlyith the volume fraction δ when it is not too large (for

< 0.8).

Fig. 5 gives the d33 of the piezoelectric composites withifferent volume fraction. When the volume fraction is com-aratively low (for δ < 0.35), the d33 is obviously under the

ig. 4. Elastic stiffness constant CD33 as a function of PMNT volume fraction.

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ig. 6. Relative dielectric constant εT33/ε0 at 1 kHz as a function of PMNT

olume fraction.

redicted value and similar phenomena appear in Fig. 3. Thisay be due to that piezoelectric composites with low vol-

me fraction of PMNT are correspondingly difficult to beoled.

Relative dielectric constant εT33/ε0 at 1 kHz as a function of

MNT volume fraction also linearly increase with the volumeraction (for δ > 0.2) as shown in Fig. 6. By using PMNT singlerystal embedded in the passive epoxy matrix, moderate εT

33/ε0s obtained. This is suitable to design a drive/receive type trans-

Fig. 7. Acoustic impedance Z as a function of PMNT volume fraction.

276 F. Wang et al. / Materials Chemistry and Physics 105 (2007) 273–277

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ig. 8. Piezoelectric constant g33 as a function of PMNT volume fraction.

ucer. Fig. 7 shows that acoustic impedance Z has similar trendith CD

33, linearly increase with the volume fraction. It can beeen that Z of the piezoelectric composites is much lower thanhat of PMNT single crystal, the principal benefit is that excel-ent acoustic matching may be achieved with a single matchingayer.

Fig. 8 shows the volume fraction dependence of piezoelectriconstant g33 for the prepared piezoelectric composites. With thencrease of the volume fraction from 0.25 to 0.7, the piezoelec-ric constant g33 varies from 120 to 80 mV/N. These are mucharger than that of PMNT single crystal and very favorable foresigning receive-type transducers.

From Figs. 3–8 the theoretical values of kt, CD33, d33, εT

33/ε0,, g33 as a function of volume fraction calculated by the mod-

fied series and parallel model [11] are all given in the solidine. The model prediction effectively indicates the trend of theroperties with the volume fraction and can give us clear instruc-ions. From the theoretical result, we can see that kt value caneach as high as 0.77(for δ = 0.57) and the maximum value of33 is 440 mV/N (for δ = 0.018). These material parameters arelose to those reported in a recent publication by Bezus et al.16]. Little differences are associated with the elastic, dielectricnd piezoelectric properties of the single crystal component.esides, compared with the theoretical results we can see that

he experiment values with low volume fraction are a little lowerhan the predicted. This may mainly result from the follow-ng reasons: the calculated volume fraction of PMNT singlerystal given in the figures is a little higher than the practical vol-me fraction. Another reason may be that the crystal constantssed for model prediction vary with different cut positions as aesult of the effect of composition segregation during the crystalrowth [14].

The strain versus electric field of 1–3 piezoelectric com-osites with the 0.56 volume fraction was measured using ainear variable differential transducer (LVDT) as shown in Fig. 9.uring the process, 5.5 kV/cm electric field was applied to the

ample at a driving frequency of 0.1 kHz under mechanical free

onditions. It should be mentioned that the tested curve was nothe first cycle of the electric field, but at least from the secondycle. According to the piezoelectric constitutive equations, d33

ig. 9. Strain vs. electric field in the 〈0 0 1〉-oriented PMNT30%/epoxy 1–3iezoelectric composites with a 0.56 volume fraction of PMNT.

alues under constant stress could be determined by the formula:

33 =(

∂S

∂E

)T

, (3)

here S, E and T represent the strain, electric field and stress,espectively. From Fig. 5 we can see that when the applied fields 5.5 kV/cm, the strain reaches about 0.08% with low hysteresis.he calculated d33 was about 1400 pC/N, which was close to thealue obtained by a ZJ-3A d33 meter. Little difference may beaused by the different measuring frequency.

. Conclusions

The lamination technique was adopted to fabricate theMNT30%/epoxy 1–3 piezoelectric composites with differ-nt volume fractions from 0.25 to 0.7. It has been provedo be an effective way to fabricate piezoelectric compositesith larger dimensions and effectively reduce the damage toMNT single crystal. The electromechanical properties of theMNT30%/epoxy 1–3 piezoelectric composites were character-

zed using the resonance method. At the 0.56 volume fraction ofMNT single crystal, a high kt of 0.8, moderate εr of 1680 andelatively low Z of 14Mrayls were achieved. These will offer sub-tantial improvements over PMNT single crystal in ultrasonicransducer applications.

cknowledgements

The research has been financially supported by the Nationalatural Science Foundation of China (Grant Nos. 50432030

nd 50602047) and Shanghai Municipal Government (Grant No.5JC14079).

eferences

[1] R.F. Service, Science 275 (1997) 1878.[2] S.-E. Park, T.R. Shrout, J. Appl. Phys. 82 (1997) 1804.

[4] S.-E. Park, T.R. Shrout, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 44(1997) 1140.

[5] T. Ritter, X. Geng, K.K. Shung, P.D. Lopath, S.-E. Park, T.R. Shrout, IEEETrans. Ultrason. Ferroelect. Freq. Contr. 47 (2000) 792.

mistry

[

[

[[

F. Wang et al. / Materials Che

[6] S. Saitoh, T. Takeuchi, T. Kobayashi, K. Harada, S. Shimanukl, Y.Yamashita, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 46 (1999) 414.

[7] R.Y. Ting, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 41 (1992)64.

[8] H. Wang, H. Xu, T. He, X. Zhao, H. Luo, Z. Yin, Phys. Status Solidi (a)

202 (2005) 2829.

[9] K.C. Cheng, H.L.W. Chan, C.L. Choy, Q.R. Yin, H.S. Luo, Z.W. Yin, IEEETrans. Ultrason. Ferroelect. Freq. Contr. 50 (2003) 1177.

10] H.P. Savakus, K.A. Klicker, R.E. Newnham, Mater. Res. Bull. 16 (1981)677.

[

[[

and Physics 105 (2007) 273–277 277

11] W.A. Smith, B.A. Auld, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 38(1991) 40.

12] J. Zola, N.J. Ramsey, United States Patent 4,514,247, April 30, 1985.13] W.A. Smith, Proceedings of the IEEE Ultrasonics Symposium, 1989, p.

755.

14] H.S. Luo, G.S. Xu, H.Q. Xu, P.C. Wang, Z.W. Yin, Jpn. J. Appl. Phys. 39

(2000) 5581.15] IEEE Standard on Piezoelectricity ANSI/IEEE Std., vol. 176, 1978.16] S.V. Bezus, V. Yu Topolov, C.R. Bowen, J. Phys. D: Appl. Phys. 39 (2006)

1919.