A Ando

A Moure

Chun-Lei Wang

EC Subbarao

HX Yan

Jia-Liang Zhang

Jian Liu

JP Mercurio

LV Korzunova

M Matsushita

Ming-Lei Zhao

R Aoyagi

RW Wolfe

RZ Hou

SJ Zhang

T Takenaka

Wen-Bin Su

Y Noguchi

Y Yao

Z Zhang

ZG Gai

Zhi-Gang Gai

ZX Cheng

ZY Zhou

Crossref

Influences of ScTa co-substitution on the propertiesof Ultra-high temperature Bi3TiNbO9-based piezoelectricceramicsZhi-Gang Gai & Ming-Lei Zhao & Wen-Bin Su &Chun-Lei Wang & Jian Liu & Jia-Liang ZhangReceived: 19 March 2013 /Accepted: 22 May 2013 /Published online: 15 June 2013# The Author(s) 2013. This article is published with open access at Springerlink.comAbstract The effect of (Sc,Ta) doping on the properties ofBi3TiNbO9-based ceramics was investigated. The (Sc,Ta)modification greatly improves the piezoelectric activity ofBi3TiNbO9-based ceramics and significantly decreases thedielectric dissipation. The d33 of Bi3(Ti0.96Sc0.02Ta0.02)NbO9was found to be 12 pC/N, the highest value among theBi3TiNbO9-based ceramics and almost 2 times as much asthe reported d33 values of the pure BTNO ceramics(~6pC/N). The high TC (higher than 900 °C) and stablepiezoelectric and dielectric properties, demonstrating thatthe (Sc,Ta) modified Bi3Ti1−xScx/2Tax/2NbO9-based materiala candidate for ultrahigh temperature applications. The new(ScTa) modification has an important typical significance,the way should be used for reference in constructing the newhigh performance materials.Keywords Bismuth layer-structured ferroelectrics .Piezoelectric ceramics . Lead free . High temperatureapplication1 IntroductionBismuth layer-structured ferroelectrics (BLSFs) ceramicsare potential candidate lead-free materials in piezoelectricdevice application, especially at high temperatures and highfrequencies application. In addition to their high Curie tem-peratures, they exhibit correspondingly low temperature co-efficients of dielectric and piezoelectric properties, low agingrate, strong anisotropic electromechanical coupling factorsand low temperature coefficient of resonant frequency, mak-ing them suitable for pressure sensors, trapped energy filters,etc [1, 2].In recent years, BLSFs have been given more attention.BLSFs, such as SrBi2Na2O9 (SBN), SrBi4Ti4O15 (SBTi),SrBi2Ta2O9 (SBT), La0.75Bi3.25Ti3O12 (BLT) etc. have beenfound to be excellent materials for nonvolatile ferroelectricrandom access memory (FRAM), owing to their fatigue freepolarization behavior [3–7]. The general formula of BLSF is(Bi2O2)2+(Am−1BmO3m+1)2−, where A is a mono-, di- or triva-lent element (or a combination of them) allowing dodecahe-dral coordination and B is a transition element with octahedralcoordination, e.g., Ti4+, Nb5+, Fe3+, W6+ or Ta5+; m is thenumber of octahedral layers in the perovskite slab, whichvaries from 1 to 6 [4, 8]. The poling of the BLSF ceramicsrequires relatively high electric field because of their highcoercive fields and the two-dimensional orientation restrictionof rotation of the spontaneous polarization.Bismuth titanate niobate (Bi3TiNbO9, hereinafter calledBTNO) (m=2), which is made up of (Bi2O2)2+ layers be-tween which (BiTiNbO7)2− layers are inserted [9], is prom-ising for high temperature piezoelectric sensors because ofits very high Tc (914 °C) [8]. However, the piezoactivity ofpure BTNO ceramics is quite low (d33<7 pC/N) [10] for hightemperature applications. The A-site substitution or/andB-site substitution have been shown to be effective in mod-ifying the structure and polarization process [11–23]. Only afew works have addressed the properties of cation-modifiedBTNO-based ceramics. For La- and Ti/W-substitutedBTNO[24] and Bi2K1/6Bi5/6TiNb2/3W1/3O9 [25] com-pounds, only a few properties (e.g., lattice parameters andTc) have been mentioned, and no detailed structural andelectrical properties have been studied. To modify BTNOstructure for improving its piezoelectricity, the ScTa co-substitution into B-site of BTNO was conducted.Z.<G. Gai (*) :M.<L. Zhao :W.<B. Su :C.<L. Wang : J. Liu :J.<L. ZhangSchool of physics, Shandong University, Jinan 250010, Chinae-mail: gzg@sdu.edu.cnJ Electroceram (2013) 31:143–147DOI 10.1007/s10832-013-9833-9The only valence of Sc is 3 and the only valence of Ta is 5,so the average valence of (ScTa) is 4 which is equal to the onlyvalence of Ti4+. The radius of Sc3+ is 0.073 nm, and the radiusof Ta5+ is 0.068 nm. They are almost the same as the radius ofTi4+ (rTi4+ =0.068 nm). More than that, Sc, Ta, Ti and Nb inthe BLSF structure have the same favorable coordinate num-ber which is 6. All of those can assure the (Sc3+Ta5+) co-substitute Ti4+ into B-site of BTNO. Because the valence ofNb is 5 which is different from the average valence of (ScTa),and the law of conservation of electric, the ScTa will not co-substitute Nb. In addition, the samples will be preparedaccording the formula Bi3Ti1−x(ScTa)x/2NbO9, so there is notlack of Nb which will lead Nb to stay at the original positionwithout being substituted .Fig. 1 Micrographs of thesurfaces of the Bi3Ti1−x(ScTa)x/2NbO9 materials. (a)x=0.00,(b) x=0.02, (c) x=0.04,(d) x=0.06Fig. 2 X-ray diffraction patternsof the Bi3Ti1−x(ScTa)x/2NbO9 ceramics. (a)x=0.00,(b) x=0.02, (c) x=0.04,(d) x=0.06144 J Electroceram (2013) 31:143–1472 ExperimentThe starting raw materials were high purity Bi2O3 (99.8 %),TiO2 (99.8 %), Nb2O5 (99.5 %), Sc2O3 (99.27 %),Ta2O5(99.5 %). The samples were prepared according theformula Bi3Ti1−x(ScTa)x/2NbO9 (x=0.00, 0.02, 0.04, 0.06).The chemicals were weighed according to the composition,and then mixed using ball milling, dried and calcined at808 °C for 3 h. After calcination, the ball-milled groundpowders were pressed into disks with 13 mm in diameterand 2 mm in thickness. Densification was achieved bysintering the disks at 1080 °C for 2 h in a sealed crucibleto prevent volatilization.The X-ray diffraction (XRD) patterns for the ceramicpowers were obtained with an X-ray diffractometer(PGeneral XD-3) patterns using Cu Kα radiation. Forroom temperature electrical and dielectric properties mea-surement, platinum electrodes (1 cm2) are fixed on bothsurfaces of the sintered pellets and fired at 800 °C for20 min in air. Samples were poled in silicone oil at200 °C under a dc electric field from 100 kV to150 kV/cm for 60–120 min. The piezoelectric coefficientd33 was measured using a quasi-static d33 meter (Instituteof Acoustics, Academia Sinica, ZJ-2). The temperaturedependence of the resistivity ρ was determined using ahigh resistance meter (Shanghai ZC43) with an appliedvoltage of 20 Volts. The planar coupling kp and thethickness coupling kt were determined by the resonance-antiresonance method by using an Impedance Analyzer(Agilent 4294A). The dielectric behavior was also mea-sured using an Impedance Analyzer (Agilent 4294A) at1000 kHz as a function of temperature.3 Results and discussionFigure 1 presents the SEM micrographs of the BTNO-basedceramics. As shown, the BTNO (x=0.00) ceramic exhibitsthe smallest grain size when compared to the (ScTa) modi-fied counterparts, indicating that the addition of (ScTa)enhanced the grain growth of the ceramics.Figure 2 shows theXRD patterns of Bi3Ti1−x(ScTa)x/2NbO9(x=0.00, 0.02, 0.04, 0.06) ceramics scanned in the range 2θ of20–60 degree. Compared with the pattern of pure Bi3TiNbO9ceramics, the Bi3Ti1−x(ScTa)x/2NbO9 (0.02, 0.04, 0.06) ce-ramics are also bismuth layer-structured ferroelectrics withm=2. From Fig. 2, the ceramics possess a pure phase oflayer-structured structure and no second phases were found,which is believed that Sc3+ and Ta5+ diffuse into the lattices toform solid solutions.Figure 3 shows the dielectric permittivity (ε/ε0) and dielec-tric loss (tanδ) measured at 1000 kHz as a function of temper-ature for the Bi3Ti1−x(ScTa)x/2NbO9-based ceramics. Asexpected, the dielectric maxima occurred over 900 °C, whichcorresponding to the Curie temperatures (TC). TC of the ce-ramics in this work gradually decreased from 913 °C to 901 °Cwith the diffusion of (ScTa)1/2 instead of Ti (rTi4+ =0.068 nm,rSc3+ =0.073 nm, rTa5+ =0.068 nm) into the lattices. The tem-perature dependence of dielectric behavior in the temperaturerange of 30–600 °C was found to be very low ∂ε∂T ¼ 0:09=-C and the dielectric loss at 600 °C and 1000 kHz was found to beless than 7 %, exhibiting the Bi3Ti0.96Sc0.02Ta0.02NbO9 ce-ramics possess high stability of the dielectric properties.Figure 4 presents piezoelectric constant d33 as a functionof temperature for Bi3Ti0.96Sc0.02Ta0.02NbO9 ceramic, inwhich one can see the two-layer BTNO orthorhombic struc-tured materials is very stable to thermal annealing. The d33of samples are measured after annealing for 1 h, and all thesamples are short-circuit during the annealing. After the d33Fig. 3 Dielectric permittivity and dielectric loss as a function of temper-ature for the Bi3Ti1−x(ScTa)x/2NbO9 ceramics, measured at 1000 kHzFig. 4 Effect of thermal depoling on d33 after annealing for 1 h of theBi3Ti0.96Sc0.02Ta0.02NbO9 ceramicJ Electroceram (2013) 31:143–147 145measurement, The same samples are put in the oven to beannealed again for the next d33 measurement. Among theScTa co-substituted BTNO, one composition, Bi3Ti0.96Sc0.02Ta0.02NbO9 with a quite high piezoelectric constant d33 of 12pC/N and an ultrahigh TC of 905 °C have been obtainedrecently by using ordinary sintering process. The value ofpiezoelectric constant d33 of the piezoelectric ceramics wasfound to be relative temperature independent to 800 °C anddrop to zero when the temperature over 905 °C, related to thede-poling temperature, which is useful for high temperatureapplications.Figure 5 shows the temperature dependence of the resistiv-ity ρ for the Bi3Ti0.96Sc0.02Ta0.02NbO9 material. The hightemperature resisitivity is important for high temperature pie-zoelectric applications and the ability to achieve high electricfield poling at high temperature. The resistivity of theBi3Ti0.96Sc0.02Ta0.02NbO9 sample is still higher than 105Ω·cm at 550 °C. That is important for its use in high-temperaturepiezoelectric devices. The activation energy Eawas calculatedaccording to Arrhenius law:ρ ¼ ρ0exp−EakT :which was found to be 1.02 eV for Bi3Ti0.96Sc0.02Ta0.02NbO9.This prove the main charge carriers of the material are oxygenvacancies.Frequency constants Np (planar frequency constant) and Nt(thickness frequency constant) for BTNO-x=0.04 materialwere found to decrease with increasing temperature, indicat-ing that the materials become softer, as shown in Fig. 6. Thereduction is very small, where Np decreases by 5.0 % of itsroom temperature value when at 620 °C, while the change forNt was found to be only 1.6 %, exhibiting very low tempera-ture coefficient of resonant frequency.Figure 7 presents electromechanical coupling factors as afunction of temperature for Bi3Ti0.96Sc0.02Ta0.02NbO9 materi-al, in which one can see the planar coupling kp is about 5 % atFig. 5 Temperature dependence of resistivity ρ for the Bi3Ti0.96Sc0.02Ta0.02NbO9 materialFig. 6 Frequency constant as a function of temperature for Bi3Ti0.96Sc0.02Ta0.02NbO9 materialFig. 7 Electromechanical coupling factors as a function of temperaturefor Bi3Ti0.96Sc0.02Ta0.02NbO9 materialTable 1 Characteristics of the Bi3Ti1−xScx/2Tax/2NbO9-based ceramicsSample x=0.00 x=0.02 x=0.04 x=0.06Tc(°C) 913 908 905 901d33(pC/N) 6 8 12 10kp 0.03 0.04 0.05 0.04kt 0.18 0.18 0.19 0.17Q 1260 1246 1270 1240tanδ(%) 0.26 0.23 0.21 0.20ε33T/ε0 110 118 126 130Np(Hz.m) 2350 2320 2291 2285Nt(Hz.m) 2130 2115 2088 2082146 J Electroceram (2013) 31:143–147room temperature, much lower than the value of thicknesscoupling kt (~ 19 %), exhibiting a strong anisotropic behavior.Both the coupling factors kp and kt were found to be relativetemperature independent to 840 °C and drop to zero when thetemperature over 890 °C, related to the de-poling temperature,which is useful for high temperature applications.The detailed properties of the Bi3TiNbO9-based materialswere characterized at room temperature and listed in Table 1.The TCwas found to be 913 °C for Bi3TiNbO9 (x=0.00) sampleand gradually decrease with the modification of ScTa. Themechanical quality factor Q of the Bi3Ti0.96Sc0.02Ta0.02NbO9ceramic were found to be higher than that of the other ceramics.The dielectric loss (tanδ) of Bi3TiNbO9-basedmaterials increasewith modification, where the tanδ of Bi3Ti0.96Sc0.02Ta0.02NbO9(x=0.04) was found to be only 0.21 %. The piezoelectricity ofthe pure BTNO was improved due to the lattice distortioncaused by the ScTa co-substitution into B-site, the d33 ofBi3Ti0.96Sc0.02Ta0.02NbO9 was found to be 12 pC/N, thehighest value among the Bi3TiNbO9-based ceramics, alsoalmost 2 times as much as the d33 values of the pure BTNOceramics (~6pC/N).4 ConclusionIn summary, Bi3TiNbO9-based materials were synthesizedusing conventional solid state processing. The dielectric andpiezoelectric properties of Bi3Ti0.96Sc0.02Ta0.02NbO9-basedceramics exhibiting a very stable temperature behavior, to-gether with its high TC ~905 °C, excellent piezoelectric coef-ficient ~12 pC/N and very low temperature coefficient ofresonant frequency, making the (ScTa) modified Bi3TiNbO9-based ceramics a candidate for ultra-high temperature appli-cations. The new (ScTa) modification of Bi3TiNbO9-basedmaterials resulted in the obvious improvement of the piezo-electric activity, having an important typical significance. Theway should be used for reference in constructing the new highperformance materials.Acknowledgments This work supported by the National Natural Sci-ence Foundation of China under the Grant Nos. 51002087, 51002097,51202132 and 51172129, China Postdoctoral Science Foundation underGrant No. 20100471500.Open Access This article is distributed under the terms of the CreativeCommons Attribution License which permits any use, distribution, andreproduction in any medium, provided the original author(s) and thesource are credited.References1. E.C. Subbarao, J. Phys. Chem. Solids. 23, 665 (1962)2. T. Takenaka, K. Sakata, J. Appl. Phys. 55, 1092 (1984)3. A. Ando, M. Kimura, Y. Sakabe, Jpn. J. Appl. Phys. 42, 520(2003)4. R.Z. Hou, X.M. Chen, J. Mater. Res. 20, 2354 (2005)5. R.Z. Hou, X.M. Chen, Solid State Commun. 130, 469 (2004)6. Y. Noguchi, I. Miwa, Y. Goshima, M. Miyayama, Jpn. J. Appl.Phys. 39, L1259 (2000)7. Y. Yao, C. Song, P. Bao, D. Su, X. Lu, J. Appl. Phys. 95, 3126(2004)8. Z. 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Influences of ScTa co-substitution on the properties of Ultra-high temperature Bi3TiNbO9-based piezoelectric ceramics

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Influences of ScTa co-substitution on the properties of Ultra-high temperature Bi3TiNbO9-based piezoelectric ceramics

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