Materials Research Bulletin 51 (2014) 167–170

Enhanced performances of sandwich structurePb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric ceramics for pulsedpower application

Hengchang Nie a,*, Xianlin Dong a,**, Xuefeng Chen a, Genshui Wang a, Hongliang He b

a Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai

200050, PR Chinab National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, Mianyang 621900, PR China

A R T I C L E I N F O

Article history:

Received 4 September 2013

Received in revised form 1 November 2013

Accepted 29 November 2013

Available online 11 December 2013

Keywords:

A. Ceramics

D. Dielectric properties

D. Ferroelectricity

A B S T R A C T

Sandwich-like structure Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric ceramics were prepared by die-

pressing technique and the microstructure, dielectric and ferroelectric properties were investigated in

the present study. It is found that the controlled pores can be well sustained in the porous layer, and for

the sandwich-like structure, high breakdown strength, resistivity and low dielectric loss are

simultaneously achieved. The resulting enhanced performances make the sandwich-like structure

ferroelectric ceramics promising candidate for pulsed power supply application.

� 2013 Elsevier Ltd. All rights reserved.

Contents lists available at ScienceDirect

Materials Research Bulletin

jo u rn al h om ep age: ww w.els evier .c o m/lo c ate /mat res b u

1. Introduction

The particular lead titanate zirconate compositionPb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT95/5) was identified as apromising ferroelectric ceramics for application in pulsed powersupplies many years ago [1–12]. At ambient conditions thiscomposition is ferroelectric (FE) phase with a rhombohedralstructure, but is near the boundary for an antiferroelectric (AFE)phase with an orthorhombic structure [13,14]. When a shock wavetravels through a poled PZT95/5 FE ceramic, the compressivepressure induces the FE phase into the AFE phase, resulting inalmost instantaneous, complete depolarization [1–12]. The avail-able stored energy density is P2

r =2e, where Pr is the remnantpolarization and e is the effective permittivity when the boundcharge releases. To obtain high energy density, it is important toproduce dense ceramics to obtain high remnant polarization. Inthis respect, porosity is generally undesired for its detrimentaldefect on the electric and mechanical properties.

In practice, it has been found that high voltage breakdowns canoccur near the front of the shock wave and through the dense PZT

* Corresponding author. Tel.: +86 21 69906091; fax: +86 21 59926384.** Corresponding author.

E-mail addresses: sestonenhc@mail.sic.ac.cn, sestonenhc@hotmail.com (H. Nie),

xldong@mail.sic.ac.cn (X. Dong).

0025-5408/$ – see front matter � 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.materresbull.2013.11.059

materials, causing the failure of the pulsed power supplies[4,5,8,12]. Studies has shown that the porous microstructurecould have a significant effect on power supply performance, withonly a relative narrow range of densities providing acceptableshock wave response. For example, Dungan and Storz reported thatthe closed pores in ceramics resulting from the addition of poreformer, are necessary to prevent high voltage breakdowns underthe shock compression, especially at low temperatures [4,12]. Thisis possibly because porous materials, compared with densecounterparts, are more efficiently to buffer shock compression[15]. However, when the porosity is beyond a limit, increasingagglomeration during mixing resulted in large flaws and an openpore structure rapidly degrade electrical and mechanical proper-ties [16]. On the other hand, for porous PZT95/5 ferroelectricceramics, pores on the both surfaces leads to the penetration ofsilver paste into the body during electrode processing.

In order to optimize the performances of the PZT95/5 ferroelec-tric ceramics in pulsed power supply, it may be desirable to combinethe high ferroelectric properties, typical of dense PZT95/5 ferroelec-tric ceramics, and high voltage breakdown resistance of porousPZT95/5 ferroelectric ceramics under shock compression. Recently,larger pyroelectric properties within functional graded materialshave been reported [17–20]. The new idea is to incorporate differentlayers with different properties thus to obtain optimized perfor-mances for a particular application. Therefore, in the present study, adense/porous/dense sandwich-like structure PZT95/5 ferroelectric

Fig. 1. Schematic diagram (a) of and scanning electron micrographs (b)–(d) of polished fracture cross section of sandwich structure PZT95/5 ferroelectric ceramic: (b) full

cross section; (c) dense layer; (d) porous layer.

H. Nie et al. / Materials Research Bulletin 51 (2014) 167–170168

ceramics were prepared and investigated. Results showed that, inthe sandwich-like structure, the high breakdown strength, highresistivity, and low dielectric loss are simultaneously achieved. Onthe other hand, the porous structure in the core layer still can bufferthe shock wave under shock compression. Therefore, the sandwich-like compound structure will exhibit desirable performances thatcannot be achieved by each single structure, making the sandwich-like structure PZT95/5 ferroelectric ceramics promising candidatefor explosively driven power supply.

2. Experimental

2.1. Preparation of samples

The sandwich structure PZT95/5 ferroelectric ceramics wereprepared by die-pressing technique. PZT95/5 powders weresynthesized from appropriate quantities of high purity oxidepowders. The raw materials were Pb3O4 of 97.33% purity(Hongzongyuan Chemical Co., Ltd., Shandong, China), TiO2 of99.44% purity (Chinaharmony Chemical Co., Ltd., Zhejiang, China),ZrO2 of 99.09% purity (Xinxing Chemical Group, Jiangsu, China),and Nb2O5 of 99.86% purity (Lingguang New Materials Co., Ltd.,Guangdong, China). The dense layer is filled with PZT95/5 powder,and the porous layer is filled with mixture of PZT95/5 powders andpolymethyl methacrylate (PMMA, (C5H8O2)n) spheres as poreformers. The addition content of PMMA is 1 wt% and the diametersof PMMA spheres were 10 mm, 20 mm, 30 mm and 60 mm,respectively. The as-prepared powders were filled into a home-made die. And then the mixture was pressed under about 200 MPainto a disk with a diameter of 20 mm. The samples were heated upto 850 8C for 1 h to assure the complete burn-out of PMMA andthen were sintered in a sealed alumina crucible at 1300 8C for 2 h ina PbO rich atmosphere to minimize the lead volatilization duringsintering. For comparison, dense PZT95/5 ferroelectric ceramicsand porous PZT95/5 ferroelectric ceramics with 1 wt% contentaddition of 30 mm PMMA spheres were also prepared. The sinteredsandwich structure samples were machined into disks withdiameter of 15 mm. The dense and porous ceramics were alsomachined into the same dimensions.

2.2. Measurements of properties

The density of the samples was determined by Archimedesmethod in deionized water. The micrographs of specimens wereobserved by TM3000 Tabletop Microscope (Hitachi, Tokyo, Japan).Ferroelectric hysteresis loops were measured by a TF Analyzer2000 (aixACCT Co., Aachen, Germany), combined with a highvoltage power supply (TReK model No. 663A). The resistivity wasdetermined using HP 4329A High Resistance Meter at roomtemperature. Each datum in this article was averaged from fivesamples respectively. A LCR meter (Model HP4284A) wasemployed to measure the tangent loss at 1 Hz in the temperaturerange from ambient temperature to 300 8C. Measurement ofbreakdown strength was conducted at room temperature insilicone oil by a digital Voltmeter.

3. Results and discussion

Fig. 1 shows schematic diagram of the sandwich-like structureand micrographs of the polished cross section of sinteredsandwich-like structure PZT95/5 ferroelectric ceramics. Fig. 1(a)is the designed schematic diagram of dense/porous/densesandwich structure, by which the powder mixtures were filledand then die-pressing was conducted. Fig. 1(b) displays the fullcross section. From the images, it can be seen the net thickness ofthe obtained sample is 1.8 mm, in which the core porous layer isabout 1 mm thick. The porous layer was well sustained betweentwo dense layers and no interlayer boundaries can be observed.The pores are in spherical shape and formed in situ. Fig. 1(c) and (d)shows the local microstructure of dense and porous layer markedby rectangles in Fig. 1(b), suggesting a grain size range of 5–12 mmand pore size around 30 mm. Besides, the measured densities ofthese samples are around 7.4–7.55 g/cm3, corresponding torelative densities of 92.5–94%, using 8.00 g/cm3 for the theoreticalmaximum density of this composition.

In Fig. 2, the ferroelectric hysteresis loops of sandwich-likestructure PZT95/5 ferroelectric ceramics with porous layer havingdifferent pore sizes are shown. For comparison, the ferroelectrichysteresis loop of dense PZT95/5 ferroelectric ceramic is also

Fig. 2. Ferroelectric hysteresis loops of sandwich structure PZT95/5 ferroelectric

ceramics with core layer having different pore sizes, at ambient temperature, 1 Hz.Fig. 4. The tangent loss of PZT95/5 ferroelectric ceramics with different structures

on temperature at 1 Hz.

H. Nie et al. / Materials Research Bulletin 51 (2014) 167–170 169

shown. The measurements were conducted at ambient tempera-ture under a frequency of 1 Hz. It can be seen that the pore size haslittle influence on the hysteresis loop characteristics. The variationof the pore size does not change the coercive fields, correspondingto the two points of intersection with the X axis. And moreimportantly the measured remnant polarizations of these archi-tectures are around 30–32 mC/cm2, slightly less than the values ofdense PZT95/5 ferroelectric ceramic, which exhibits a remnantpolarization of 33.5 mC/cm2. Therefore, these architectures still canexhibit good ferroelectric properties, which is important for itsapplications in pulsed power supply.

The comparison of resistivity between the dense, porous andsandwich structure PZT95/5 ferroelectric ceramics is illustrated inFig. 3. Here the data when pore size equals zero represents thevalue of dense PZT95/5 ferroelectric ceramic. It can be seen that theresistivity of the sandwich structure PZT95/5 ferroelectricceramics is on the scale of (1.2–1.4) � 1012 V cm, similar to thatof dense PZT95/5 ferroelectric ceramic with an average value of1.5 � 1012 V cm. However, the resistivity of the porous PZT95/5ferroelectric ceramics is on the scale of (0.2–0.4) � 1012 V cm.

Fig. 3. The resistivity of PZT95/5 ferroelectric ceramics with different structures.

Therefore, compared with the porous PZT95/5 ceramics, theresistivity of sandwich-like structure was enhanced by one order,similar to the dense counterpart. This is important for improvingthe DC breakdown strength, and thus decreasing the probability ofbreakdown in the prepoling process during the preparation ofporous ceramics. Generally, in dielectrics, high resistivity willlower the dielectric loss, which will be found in Fig. 4.

The dielectric tangent losses of the PZT95/5 ferroelectricceramics with different structures as function of temperaturewere shown in Fig. 4. The two peaks in the tangent loss curvescorrespond to the low temperature ferroelectric phase to hightemperature ferroelectric phase and high temperature ferroelectricphase to paraelectric phase, the latter is the Curie point of theferroelectric ceramics. We can see that there is no observeddifference for each the two temperatures for all specimens. Thissuggests that the structure imposes no effect on the phasetransition of PZT95/5 ferroelectric ceramics. More importantly,little disparity can be observed from the dielectric losses betweenthe dense and sandwich structure PZT95/5 ferroelectric ceramics.At ambient temperature, the dielectric losses of dense andsandwich structure PZT95/5 ferroelectric ceramics are on thescale of 2.0–2.2%, while the dielectric loss of porous PZT95/5ferroelectric ceramics is bigger, on the scale of 2.4–2.6%. Therefore,the sandwich-like structure PZT95/5 ferroelectric ceramics canobtain similar tangent loss to dense PZT95/5 ferroelectric ceramics.

In Fig. 5, the dielectric breakdown strength of PZT95/5ferroelectric ceramics under DC voltage is illustrated. Here thedata when pore size equals zero represents the breakdownstrength of dense PZT95/5 ferroelectric ceramic. It is obvious thatthe breakdown field for dense PZT95/5 ferroelectric ceramics,5.7 kV/mm, is higher than sandwich structure counterparts of5.4 kV/mm, 5.5 kV/mm, 5.3 kV/mm and 5 kV/mm, respectively.Therefore, compared with dense PZT95/5 ferroelectric ceramics,the breakdown fields of sandwich structures decrease by about10%. While in a previous work, compared with the dense samples,breakdown fields of porous PZT95/5 ferroelectrics decreased by20% [21]. This is very important for its application in pulsed powersupply, because high electric breakdown thresholds can signifi-cantly increase the output voltage of power supply [4,12,22].Improvements in electric breakdown strength of ferroelectricmaterials can allow us to build power supplies with higherreliability and smaller volumes. Therefore, the increased break-down strength of sandwich-like PZT95/5 ferroelectric ceramics

Fig. 5. The breakdown strength of sandwich structure PZT95/5 ferroelectric

ceramics with core layer having different pore sizes, at ambient temperature, 1 Hz.

Here the value when pore size equals zero represents the breakdown strength of

dense PZT95/5 ferroelectric ceramic.

H. Nie et al. / Materials Research Bulletin 51 (2014) 167–170170

makes the structure PZT95/5 ferroelectric ceramics promisingcandidate for pulsed power supply.

4. Conclusions

A dense/porous/dense sandwich structure PZT95/5 ferroelectricceramics were prepared and investigated. Results showed that, inthe structure, the high breakdown strength, high resistivity, andlow dielectric loss are simultaneously achieved. The newsandwich-like architecture combines the high electrical proper-ties, typical of dense PZT95/5 ferroelectric ceramics, and promisinghigh voltage breakdown resistance of porous PZT95/5 ferroelectricceramics under shock compression, making the structure PZT95/5

ferroelectric ceramics promising candidate for explosively drivenpower supply.

Acknowledgements

This work was supported by the National Nature ScienceFoundation of China (Grant No. 51202273) and the Nature ScienceFoundation of Shanghai (Grant No. 12ZR1435400).

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