Piezoelectric,ferroelectric and mechanical properties of lead zirconate titanate/zinc oxide nanowhisker ceramics
Da-Wei Wang •Mao-Sheng Cao •Jie Yuan •Quan-Liang Zhao •Hong-Bo Li •Hai-Bo Lin •
De-Qing Zhang
Received:24October 2010/Accepted:3February 2011/Published online:26February 2011ÓSpringer Science+Business Media,LLC 2011
Abstract New lead zirconate titanate/zinc oxide nano-whisker (PZT/ZnO w )ceramics were fabricated by a con-ventional solid state processing and their structures,piezoelectric,ferroelectric and mechanical properties were studied.Both the PZT perovskite and ZnO phas can be obrved from the X-ray diffraction patterns.The grain size of ceramics is reduced due to the ZnO w addition.The incorporation of ZnO w into the PZT ceramics improves the strength and toughness,while deteriorates the piezo-electric and ferroelectric properties.For the PZT/ZnO w ceramics with 1–2wt%ZnO w ,the mechanical properties become optimum,meanwhile maintain good piezoelectric and ferroelectric properties:r c =376–484MPa,r f =115–121MPa,K IC =1.41–1.54MPa m 1/2,d 33=442–490pC/N,k p =0.54–0.55,e r =3,322–3,980,Q m =99–101,tan d =1.6%–1.7%,P r =21.5–26.9l C/cm 2and E c =8.1–8.6kV/cm.
1Introduction
Lead zirconate titanate (PZT)piezoelectric ceramics exhibit excellent piezoelectric properties and are extensively ud in
applications of numerous electronic devices,such as actua-tors,nsors,capacitors,resonators and high-power trans-ducers [1–7].However,piezoelectric ceramics suffer from the low mechanical strength and the reliability under vere circumstances [8–11].Several approaches to improve mechanical properties have been ud to investigate incor-porating polymers,metals,fibers or whiskers etc.[12–19].Nhuapeng et al.[18]have studied the PZT-bad composites incorporating polymers.Hwang et al.and Li et al.have carried out the PZT/metal ceramics with Ag and Pt particles,respectively [15,20].Although the mechanical properties of the PZT-bad composites were reinforced,electrical properties were deteriorated greatly.Therefore,it is neces-sary to design the microstructure of the PZT posssing excellent mechanical properties without dramatically degrading electrical properties.
In light of novel applications bad on the mi-con-ducting and piezoelectric properties of ZnO nanostructures [21],Wang et al.have noted that the piezoelectric power generators bad on ZnO na
nowire arrays might be able to convert mechanical energy into electrical energy.Such devices could provide flexible power sources with potential applications in nsors,actuators and microelectrome-chanical systems (MEMS),etc.[22].As a result,nano-structured ZnO is a suitable piezoelectric material for electromechanical energy conversion.ZnO nanowhiskers (ZnO w ),due to the high-temperature strength and excellent chemical stability,have received much attention for industrial applications as reinforced composite materials [23–28].Therefore,it is expected that ZnO w embedded in the PZT-bad ceramics would be a good solution to improve the mechanical behavior without deteriorating electrical properties verely.
In this work,PZT-bad ceramics embedded with ZnO w were prepared by a normal sintering process.The effects of
D.-W.Wang ÁM.-S.Cao (&)ÁQ.-L.Zhao ÁH.-B.Li ÁD.-Q.Zhang
School of Materials Science and Engineering,Beijing Institute of Technology,100081Beijing,China e-mail:caomaosheng@bit.edu
J.Yuan
School of Information Engineering,Central University for Nationalities,100081Beijing,China e-mail:
H.-B.Lin
China Astronautics Standards Institute,100071Beijing,China
J Mater Sci:Mater Electron (2011)22:1393–1399DOI 10.1007/s10854-011-0319-8
ZnO w on the microstructures,piezoelectric,dielectric, ferroelectric and mechanical properties of PZT are inves-tigated.The reinforcement mechanisms of ZnO w on the mechanical respons of PZT are discusd.
2Experimental
2.1Sample preparation
The fabrication of PZT/xZnO w(x=0,1,2,5,8,10wt%) ceramics were performed by a conventional solid state reaction sintering.ZnO w was synthesized by combustion oxidation offine zinc powders(purity99.999%)without any catalysts or additives.Detailed discussions on the synthesis of Z
nO w have been reported elwhere[29].A commercially available PZT powder(PZT-5MN,Hongsheng Industry, Baoding,China)was ud as the raw material.Appropriate amounts of the powders mixed with the as-fabricated ZnO w for the designated ceramics were ball-milled for24h with zirconia balls as the grinding media and alcohol as the sol-vent.After milling,the slurry was dried at room temperature and then the dried powders were mixed with proper poly-vinyl alcohol(PVA)liquid binder addition.The mixed powders were compacted under a pressure of200MPa by die pressing.After binder was burned out in a furnace,the green compacts were sintered at1,150°C for2h in a clod alumina crucible that contained PbZrO3powders to mini-mize lead volatilization.For electrical measurements,silver paste was printed to form electrodes on both sides of the sintered samples,which were subquentlyfired at800°C for10min.Poling treatment was carried out in silicon oil at 120°C for20min with an electricfield of3kV/mm.春羽图片
2.2Characterization
The bulk density was determined by the Archimedes method in distilled water.The crystalline phas of the sintered samples were examined by the X-ray diffraction (XRD)with Ni-filtered Cu K a radiation.Morphologies of the nanowhiskers and ceramics were studied by a scanning electron microscope(SEM).
The piezoelectric properties were measured by using the ZJ-3AN piezoelectric tester,and electromechanical and dielectric characteristics were calculated with a Model HP 4194impedance analyzer.The hysteresis loops and ferro-electric properties were measured using a Radiant Preci-sion Workstation ferroelectric tester system.
For the Fracture toughness K IC,a single-edge notched beam test was ud with a cross-head speed of0.05mm/min and a span of20mm on the samples with294920mm. Compression tests were performed on a CSS-2220testing machine using cylinders with12mm in diameter and 4.2mm in thickness.Theflexural strength was determined using the three-point bending method on a 394936mm bar with a span of30mm and a cross-head speed of0.5mm/min.
3Results and discussion
Figure1shows the SEM images of ZnO nanowhisker synthesized by the simple combustion oxidation method without any catalysts or additives.It can be clearly en that ZnO w is uniform and has tetra-needle-like nanostruc-tures.The individual structure consists of needle-shaped legs with high aspect ratios.The thickness of narrow tips is some decades of nanometer and the length is about10l m.
Figure2shows the XRD patterns of the ZnO w and PZT/ ZnO w ceramics with various amounts of Zn
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O w,respec-tively.A ries of characteristic peaks of pure PZT and ZnO are obrved.The diffraction peaks of ZnO in the ceramics gradually intensify with the increa of ZnO w content from0to10wt%,indicating that the PZT matrix is a pha compatible with ZnO w.In addition,no othertfboys歌曲大全
peaks Fig.1SEM micrographs of the ZnO w microstructures
but the PZT and ZnO are obrved in the XRD spectrum,indicating that there is no significant chemical reaction occurring between PZT and ZnO w during sintering at 1,150°C.
Figure 3shows the SEM images of the typical fracture surfaces of PZT/ZnO w ceramics with various ZnO w con-tents.All the sintered ceramics become den and the grain boundaries are distinct.It is obrved that the grain size of the PZT/ZnO w ceramics is much smaller than that of the PZT ceramics.The grain size is found to decrea from 15–20l m for the PZT to about 10l m for 2and 5wt%
ZnO w ,and then about 8l m for 8wt%ZnO w ceramics.It is suggested that the grain growth of the PZT/ZnO w ceramics is effectively limited by the incorporation of ZnO w in the PZT matrix.In addition,changing of fracture mode could also be easily obrved.The fracture mode of the PZT ceramics is completely intergranular,while the fracture mode of the PZT/ZnO w ceramics changes from completely intergranular to partially intragranular.It is revealed that purpoly initiated cracks in the PZT ceramics propagate mostly along intergranular and interpha boundaries,as shown in Fig.3a.However,with addition of ZnO w ,the cracks propagate partially in the intragranular mode (Fig.3b–d)and the fracture path is significantly extended into polypha sinters [30].
The relative densities of PZT/ZnO w ceramics are listed in Table 1.All highly den bodies of the PZT/ZnO w ceramics are obtained at more than 96%of the theoretical density value.With the increa of ZnO w content,the relative den-sities of the ceramics change slightly.The mechanical properties of PZT/ZnO w in terms of compressive strength r c ,flexural strength r f and fracture toughness K IC are investigated as shown in Fig.4and the values are listed in Table 1.It can be en that the mechanical characteristics of the PZT/ZnO w ceramics are superior to tho of the PZT ceramics.Particularly,the PZT/ZnO w ceramics with 2wt%ZnO w posss the maximum mechanical properties with compressive strength of 484MPa,flexural strength of 121MPa and fracture toughness of 1.54MPa m 1/2.
The strength enhancement of the PZT/ZnO w over the PZT ceramics is mainly associated with the grain
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Fig.3SEM micrographs of the PZT/ZnO w ceramics with
a 0wt%,
b 2wt%,
c 5wt%an
d d 8wt%ZnO w
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reduction due to the incorporation of ZnO w as shown in Fig.3,which can be described by the Hall–Petch equation r f¼r0þkdÀ1=2;ð1Þwhere r0,k and d reprent the resistance for deformation in crystal,influence parameter of grain boundary and average grain size,respectively.As is en in Fig.3,with the addition of ZnO w,the grain size of PZT decreas obviously,which lead to the increa of strength according to Eq.1.On the other hand,the improvement of fracture toughness is probably attributed to the contributions of the whisker bridging and pull-out[31].Figure5shows the typical micrographs of ZnO w in the PZT ceramics and the corresponding schematic illustrations of the reinforce-ment mechanism,such as whisker pull-out(Fig.5a)and bridging(Fig.5b).During the whisker pull-out,the energy that will normally cau crack propagation is partially expended by debonding and friction as the whisker slid against adjacent microstructure features[32].This can effectively increa the fracture toughness.In addition, according to the elastic fracture mechanics[33],the bridging mechanism of PZT/ZnO w ceramics clearly rep-rents an intrinsically higher energy source of fracture resistance for matrix grains.Many rearchers[34]have reported that the increa of fracture toughness is mostly achieved by changing the mode of crack propagation in
the ca of ceramics,when the increa of effective fracture energy may occur.It can be easily obrved that the pur-poly initiated cracks propagate mostly along the inter-granular boundaries of the PZT ceramics shown in Fig.3a. However,for the PZT/ZnO w ceramics,cracks partially break through the sintered ceramic grains and propagate in the intragranular mode shown in Fig.3b–d.As a result,the incorporation of ZnO w is effective in suppressing the crack propagation[30]and changing the fracture modes of the PZT ceramics,which leads to the improvement of fracture toughness[35].Furthermore,as shown in Fig.4,when the content of ZnO w is over2wt%,all mechanical properties of PZT/ZnO w decrea obviously,which is probably attributed to the agglomeration of ZnO w[36,37].
The piezoelectric and dielectric properties of PZT/ZnO w ceramics are shown in Figs.6and7and the values are listed in Table2.With the increa of ZnO w content,the piezoelectric constant d33,electromechanical coupling factor k p and relative dielectric constant e r of the ceramics generally decline from550pC/N,0.59and4,895to195 pC/N,0.29and2,336,while the mechanical quality factor Q m and dielectric loss tan d greatly increa from71and 2%to112and6.8%,respectively.
The variation of piezoelectric and dielectric properties is believed to be affected by the domain clamping caud by the significant reduction of grain size as shown in Fig.3 [38].As a result of the re
duced grain size,the domain switching in PZT is prevented by domain clamping,lead-ing to the insufficiency of poling and the decline of pie-zoelectric properties[38].Moreover,the low-piezoelectric properties of ZnO w in PZT matrix can be another reason for the decrea of piezoelectric and dielectric constants [31].However,the PZT/1–2wt%ZnO w ceramics with excellent mechanical and electrical properties posss lower tan d and higher Q m than tho of the PZT,which is quite attractive to the application of PZT in electronic devices.
黑茶是什么茶Ferroelectric hysteresis behavior was studied for all the compositions of PZT/ZnO w ceramics at room temperature, which has been shown in Fig.8.The variations of remnant polarization P r,saturation polarization P s,coercivefield E c and remnance ratio P r/P s determined from the hysteresis
Table1Mechanical properties of PZT/ZnO w ceramics
ZnO w content (wt%)Relative
density(%)
r c
(MPa)
r f
(MPa)
K Ic(MPa m1/2)
096.525284 1.12
196.6376115 1.41
296.4484121 1.54
596.529298 1.42
896.830792 1.36
1096.3420102
1.37
Fig.4Variations of a r c,b r f and c K IC for different compositions of PZT/ZnO w ceramics
loops are shown in Fig.9and the values are listed in Table 3.It is obrved that as the content of ZnO
w increas,P r decreas from 33.1to 13.1l C/cm 2and the E c increas from 7.4to 9.3kV/cm for the PZT/ZnO w ceramics.Domain switching becomes harder due to the incorporation of ZnO w and reduction of grain size,
resulting in lower polarization as evidenced by the decrea in P r and P s .P r /P s is found to decrea with the increa of ZnO w content,which indicates that squareness of the P –E loop decreas [39
].
Fig.5Typical micrographs of the ZnO w in the PZT matrix and the corresponding schematic illustration of the reinforcement mechanism:a whisker pull-out and b whisker
bridging
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Fig.6Variations of a d 33,b k p and c Q m for different compositions of PZT/ZnO w
ceramics
Fig.7Variations of a e r and b tan d for different compositions of PZT/ZnO w ceramics
Table 2Piezoelectric and dielectric properties of PZT/ZnO w ceramics
ZnO w content (wt%)d 33
(pC/N)
Q m k P e r tan d 0550710.594,895 2.01
490990.553,980 1.624421010.543,322 1.753141180.422,921 2.082271140.332,458 3.710
195相约西藏
112
0.29
2,336
6.8
