Bi-Tunable Dielectric Constant of Antiferroelectric PZT
Ceramics Under DC Electric Field
Jinfei Wang,Tongqing Yang,†Kun Wei,Gang Li,and Shengchen Chen Functional Materials Rearch Laboratory,Tongji University,Shanghai200029,China
The dielectric properties of(Pb0.85Ba0.11La0.03)(Zr0.76Sn0.20Ti0.04) (PLZST–B11)composite ceramics have been investigated sys-tematically.The characteristic of PLZST–B11was that it demon-strated antiferroelectricity.The dielectric constant incread, then decread sharply with increasing DC electricfield,and a low loss also was obtained under DC electricfields(40kV/cm). The low loss(tan d~0.003)and the highest tunability(~65%)were obtained for the PLZST–B11ceramics around50°C,indicating that it is a promising candidate for bi-tunable materials nearby room temperature.The dielectric properties of PLZST–B11 composites under a DC biasfield can be uful for the design of devices and practical applications.
I.Introduction
I N recent years,electric-field tunable materials have been
extensively studied,1–6lots of rearch work have been carried out on barium titanate-bad perovskites system which exhibits a large dielectric constant change under DC bias electricfield.7–9The strong dependence of the dielectric properties on the electricfield can be employed to develop tunable microwave devices such asfilters,varactors,delay lines,and pha shifters.10,11The critical material parameters for many microwave designs are low-dielectric constant for impedance matching,low-dielectric loss tangent,and high-dielectric tunability in a certain electric-field range.12,13The high-dielectric loss and high-dielectric constant of ABO3have restricted its application.Furthermore exploration on new materials is desirable in developing tunable devices.14,15 Antiferroelectric materials,for example,PZT,have recently received renewed attention due to their high-electric performance.16The prent authors found that the system has high-dielectric constant and low loss nearby relative low temperature.It is interesting to study the electric-field bi-tun-ability of the dielectric constant and the dielectric loss under DC bias for the system.That is,under DC bias for the sys-tem,the dielectric constant incread and then decread sharply with increasing DC electricfield.Dielectric constant not only increas,but also decreas under DC electricfield, It is called bi-tunability,and the change point was at ~40kV/cm.In this work,we study the electricfield depen-dence of the dielectric constant and loss of(Pb0.85Ba0.11 La0.03)–(Zr0.76Sn0.20Ti0.04).The results show that high tun-ability and reasonably low loss have been obtai
ned around 50°C,indicating that it is a promising candidate for the elec-tric-field tunable materials.
II.Experimental Procedure
Using methods of the solid-state reaction with raw materials Pb3O4(99.0%),BaCO3(99.0%),TiO2(99.0%),ZrO2(99.0%), SnO2(99.5%),La2O3(99.99%)(Pb0.85Ba0.11La0.03)(Zr0.76Sn0.20Ti0.04) ceramics were prepared.The mixed powders were calcined at 900°C for2h.The calcined powders were mixed with addition of alcohol again,dried and presd into10mm diameter pel-lets,and sintered at1240°C for3h.All samples had densities higher than90%of their theoretical limits.The sample crystal-lization behavior was examined using an X-ray diffractionme-ter(XRD,D8Advance;Bruker AXS GmbH,Karlsruhe, Germany)and scanning electron microscopy(SEM,JSM-5510;JEOL,Tachikawa,Tokyo,Japan).The sintered pellets were polished to~1.0mm in thickness for normal dielectric measurement and0.2mm in thickness for biasfield depen-dence measurement.Silver electrodes werefired on both sur-faces of the specimens for electric measurement.Dielectric properties were characterized using two precision LCR meters from1Hz to1000kHz in the temperature rangeÀ40°C–140°C at a rate of3°C/min.(HP4284A and HP4294A;Hewlett-Packard,Beijing,China)and a lab-established computer controlled e–E analyzer system which includes an LCR meter (TH2816;Tonghui Electronic Instrument Corp.,Changzhou, Chi
na),a high-voltage generator(YJ93A;Shanghai Scientific Instrument Rearch Institute,Shanghai,China),and a sample chamber.
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III.Discussion
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Figure1shows veral typical polarization-electricfield hys-teresis loops(P–E hysteresis loops)of PLZST–B11at differ-ent temperatures.As shown,a classic double-hysteresis loop characteristic of AFE pha was obrved.The largestfield applied to the PLZST–B11is70kV/cm,and it is shown that the dielectric breakdownfield was large.Conquently,it is shown that the polarization of PLZST–B11increas with increasing temperature.Obviously,the antiferroelectric pha transforms to paraelectric pha above40°C with increasing of temperature gradually.
The temperature dependence of the dielectric constant(e)and loss(tan d)for the PLZST–B11sample at1,10,50,100kHz is shown in Fig.2.A dielectric peak occurs at50°C(>2300),and no frequency dependence is prent near the dielectric constant max-imum.The loss tan d is>0.001above50°C.
To understand the DC electricfield effect on the dielectric properties of PLZST–B11ceramics,dielectric properties were measured at different DC bias levels in the temperature range 30°C–80°C as described earlier.The DCfield dependence of e at different temperatures for the
sample is shown in Fig.3, respectively.
As depicted in Fig.3,electric constant changed identically, it incread then decread with increasing electricfield.The dielectric constant was about2000with E=0V/cm,which incread sharply with increasing the electric-field.At50°C,
M.W.Cole—contributing editor
Manuscript No.30825.Received December19,2011;approved January27,2012.
†Author to whom correspondence should be addresd.e-mail:yangtongqing@ tongji.edu
1
J.Am.Ceram.Soc.,1–3(2012) DOI:10.1111/j.1551-2916.2012.05129.x ©2012The American Ceramic Society
J ournal
the maximum of e (~6000)were obtained at 50kV/cm,the rate of change of the dielectric constant wa
s up to 3times.The variation feature of e and the stable electric field behav-ior,are promising features of PLZST –B11ceramics as a bi-tunable material for practical applications.
The tunability is determined by finding the change in dielectric constant with an applied DC bias compared to tho dielectric values at zero field at a given temperature,using the equation 2
Tunability ð%Þ¼½e ðE 0ÞÀe ðE Þ =e ðE 0ÞÂ100%;
ð1Þ
where E 0=0kV/cm and E is the electric field at which we calculate the tunability.
It can be en from the Fig.4that PLZST –B11tunability is incread with the increasing DC bias ( ~50kV/cm),and then decread with the increasing DC bias(>~50kV/cm).At the temperature 50°C(T m)where the dielectric maximum occurs Click here to enter text.the loss are high around T m.But above the temperature T m,becau of the constant low loss on the order of 10À3in the PLZST –B11ceramics suitable dielectric properties can be tailored in the tempera-ture range from 30°C to 80°C.Tunability exhibits the highest value of ~65%at 50°C.At 30°C –60°C,the tunability exhibits a higher value of ~60%.At 30°C,e =4500,tunabil-ity =55%,and at 60°C,e =5000,tunability =62%were obtained.Then,with increasing temperature,tunability was decread above 60°C sharply.
In summary AFE (Pb 0.85Ba 0.11La 0.03)(Zr 0.76Sn 0.20Ti 0.04)ceramics were prepared using conventional solid-state route.The PLZST AFE ceramics exhibited excellent dielectrical properties and suitable bi-tunability under DC electric field.By applying a DC bias on the samples simultaneously,the dielectric constant incread and then decread sharply to 2000,the maximum value was ~6000at 50kV/cm,the bi-tunability was up to 65%.
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IV.Acknowledgments
This work was supported by the Nature Science Associate Foundation (NSAF)of China (Grant No.10874130).The Key Project of Chine Ministry of Education (No.108055),Shanghai Pujiang Program and the State Key Laboratory of Electronic Thin Films and Integrated Devices (UESTC).
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