Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage

  • Published on

  • View

  • Download


  • PS











    Materials Science and Engineering B 178 (2013) 1509 1514

    Contents lists available at ScienceDirect

    Materials Science and Engineering B

    jou rn al hom ep age: www.elsev ier .com/ locate /mseb

    reparation and dielectric properties of BaCu(B2O5)-dopedrTiO3-based ceramics for energy storage

    ingxia Li , Xiaoxu Yu, Haocheng Cai, Qingwei Liao, Yemei Han, Zhengdong Gaochool of Electronic and Information Engineering, Tianjin University, Tianjin 300072, China

    r t i c l e i n f o

    rticle history:eceived 29 March 2013eceived in revised form 21 August 2013ccepted 28 August 2013vailable online 8 September 2013

    eywords:rTiO3 ceramics

    a b s t r a c t

    BaCu(B2O5) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions dopedSrTiO3 ceramics effectively from 1300 C to 1075 C by conventional solid state method. The effect of BCBcontent on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. Theaddition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant.The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and morehomogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained

    aCu(B2O5)interingreakdown strength

    a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effectscaused by the presence of second phases and the incorporation of Cu2+ and Ba2+, while further increasewas owing to the increase of dissolved Ba2+ ions when the content of BCB is more than 2.0 mol%. Themulti-ions doped SrTiO3 ceramics with 1.0 mol% BCB addition showed optimal dielectric properties asfollows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy

    3 energ

    density of 1.05 J/cm and

    . Introduction

    Dielectric materials for energy storage capacitors have a wideange of applications in power electronics, pulsed power applica-ions, high-power microwave systems and hybrid electric vehicles14]. In these systems, energy storage capacitors perform manyital functions, e.g., in hybrid electric vehicles, capacitors canmprove the durability and reliability of electric systems; meet theeak power needs; and keep internal combustion engines energyfficiency when operating.

    For energy storage materials, energy density is the most impor-ant criteria, which is calculated by [5]:

    = P2


    EdP = E2


    0r(E)EdE (1)

    here P is the polarization, 0 is the dielectric constant in vac-um, and r(E) is the relative dielectric constant at an electric fieldE). We see from Eq. (1) that energy density is determined by the

    reakdown strength (BDS), dielectric constant, and the dielectricunability (the variation of dielectric constant with the electriceld).

    Corresponding author. Tel.: +86 022 27402838.E-mail address: (L. Li).

    921-5107/$ see front matter 2013 Elsevier B.V. All rights reserved.ttp://

    y efficiency of 98.83%. 2013 Elsevier B.V. All rights reserved.

    Many types of dielectric materials have been used for energystorage, which can be divided into three classes: the low- materials(magnitude of 1 and 10), the high- materials (magnitude of 103),and the medium- materials (magnitude of 102).

    Polymers are the typical materials that own low-. These materi-als generally possess high breakdown strength and energy density.However, the low- goes against the reducing of module sizeand these materials usually have limitations in machining oper-ation and packaging. The representative materials with high- areferroelectric and antiferroelectric ceramics (e.g. BaTiO3, PbZrO3),these materials generally have low breakdown strength and largedielectric tunability, which restrict their energy densities. The rep-resentatives of typical medium- materials are non-ferroelectricceramics (e.g. SrTiO3). SrTiO3 ceramic represents a good compro-mise between breakdown strength and dielectric constant, and haslow dielectric tunability, which are good for the energy density.

    Due to its good performance in energy storage, SrTiO3 ceramichas been investigated extensively. Shende et al. [6] reported theimproved breakdown strength of SrTiO3 thick film (100150 m,BDS = 35 V/m). Shen et al. researched the rare earth ions dopedSrTiO3 ceramics, they discussed the heterovalent doping in A-site ofSrTiO3 and obtained a high dielectric constant (>3000) [710]. Wuet al. [11] reported that the Sr(Ti0.95Zr0.05)O3 shows good dielec-

    tric properties (r 330, BDS 14.5 kV/mm). Dong et al. studiedthe Ba0.3Sr0.7TiO3 doped with 1.6 wt% ZnO and improved the BDSfrom 31 kV/mm to 40 kV/mm [2]. In our previous study, excel-lent dielectric properties were obtained for the multi-ions doped

  • 1 ngineering B 178 (2013) 1509 1514










    phase. The formation of Cu2O phase is due to the reducing actionof CuTi which are created by the substitution of Cu2+ into Ti4+

    sites. With the increase of BCB content, the second phases of CuO

    510 L. Li et al. / Materials Science and E

    rTiO3-based ceramics (hereafter MST, 88.0%SrTiO3-2.0%CaZrO3-0.0%MgTiO3), however, high sintering temperature of 1300 Cinders its application.

    Medium sintering temperature has superiority in environmen-al protection and ensures the feasibility of low-cost electrode

    aterial (e.g. Ag-Pd alloy) in multilayer ceramic capacitors (MLCC).p to now, several compounds with low melting point were used

    o decrease the sintering temperature of SrTiO3-based ceramics1214]. However, the addition of additives decreases the dielectriconstant to a certain extent [1214]. In terms of ceramics used fornergy storage, the dielectric constant and the breakdown strengthre expected to be as high as possible. Therefore, a sintering addi-ive that could decrease the sintering temperature and improvehe breakdown strength while not sacrifice the dielectric constants highly required.

    In this paper, BaCu(B2O5) with a low melting point of 850 C15] was added to the MST ceramics to decrease the sinteringemperature. The effect of BCB content on the phase constitution,

    icrostructure and dielectric properties were investigated. Finally,he energy densities of BCB-added MST ceramics were discussed.

    . Experiment method

    Specimens were prepared through conventional solid stateethod. SrTiO3, CaZrO3 and MgTiO3 were synthesized separately

    y using reagent SrCO3 (99.0%), TiO2 (99.0%, rutile), CaCO399.0%), ZrO2 (99.0%), and MgO (98.0%). The three mixturesere all milled with de-ionized water and zirconia balls for 12 h,

    hen dried, and calcined at 1125 C for 4 h, 1000 C for 2 h and00 C for 3 h, respectively. BaCO3 (99.0%), CuO (99.0%) and B2O399.0%) were mixed and milled in a nylon jar with zirconia balls,ried, and then calcined at 700 C for 4 h to synthetize BaCu(B2O5).he calcined powders were weighed and mixed according tohe desired stoichiometry as follows: 88.0%SrTiO3-2.0%CaZrO3-0.0%MgTiO3 + x BCB (x = 0.0, 1.0, 2.0, 3.0, 5.0 mol%). The mixturesere milled, dried, and pressed into pellets. The undoped pelletsere sintered at 1300 C and the others were sintered between

    025 C and 1100 C in air for 4 h.The density measurements were performed using the

    rchimedes method (Mettler Toledo XS64). The crystallinetructures of the sintered samples were analyzed by X-ray diffrac-ion (Rigaku D/MAX-2500) using Cu K radiation at a 0.02/0.5 scanning speed. Microstructure observations and analyses of sin-ered surfaces were performed by field emission scanning electron

    icroscopy (Hitachi S-4800) associated with energy dispersivepectroscopy (EDS).

    Before electrical measurement, specimens were coated withilver electrodes on both faces. The dielectric constants were mea-ured with LCR (HP4278A) at 1 MHz. The insulation resistancesere measured using a high resistance meter (Agilent 4339B).

    he breakdown strengths were measured by using breakdowntrength testing instrument (CJ2677A) to apply DC voltage auto-atically, and the specimens for BDS measurement were polished

    o 0.35 0.03 mm in thickness.

    . Results and discussions

    Fig. 1 shows the densities of MST + x BCB ceramics with.0 x 5.0 mol% as a function of sintering temperature. The densi-ies increased when sintering temperature increased from 1025 Co 1075 C and reached the saturated values when sintering tem-

    erature was above 1075 C. Thus, we believed that 1075 C is theptimal sintering temperature for all samples. Considering that theptimal sintering temperature is 1300 C for pure MST, the additionf BCB decreases the sintering temperature effectively. It is because

    Fig. 1. Bulk densities of MST + x BCB ceramics with 1.0 x 5.0 mol% as a functionof sintering temperature.

    BCB melts during the sintering process since the melting point islow (850 C) and the liquid phase promotes the densification ofceramic samples at a low temperature.

    The XRD patterns of MST + x BCB ceramics with0.0 x 5.0 mol% sintered at their optimal temperatures aregiven in Fig. 2. And the inset in Fig. 2 shows the enlarged view ofpeak (2 0 0). All samples maintained the cubic perovskite structurewith different second phases. When the BCB content was low(2.0 mol%), the second phases of CuO and Cu2O were detected.This is probably due to the volatilization of boron when the sin-tering temperature is up to 1075 C. As reported [16], BaCu(B2O5)owns monoclinic system of space group C2. The Cu2+ ions areequivalent with the arrays of highly distorted [CuO4] squares andconnect through double-triangular [B2O5] groups to form the(0 0 1) plane and the Ba atoms interleave successive layers. Whenthe content of BCB is low, the volatilization of boron accounts fora significant proportion. It is possible that the (0 0 1) plane suffersa severe damage, and a large amount of Cu2+ and Ba2+ ions getisolated. Consequently, some Cu2+ and Ba2+ ions are incorporatedinto the matrix, which are proved by the peak shift shown in theinset of Fig. 2 and the variation of lattice parameter as discussedbelow, and some Cu2+ ions crystallize into CuO phase and Cu2O

    Fig. 2. XRD patterns of MST + x BCB ceramics with 0.0 x 5.0 mol% sintered at theiroptimal temperatures. Inset is the enlarged view of peak (2 0 0).

  • L. Li et al. / Materials Science and Engine

    Fig. 3. Variations of dielectric constant and lattice parameter of MST + x BCB ceram-i




    Fig. 7 shows the capacitancevoltage (CV) loops of MST + x BCB

    cs with 0.0 x 5.0 mol% sintered at their optimal temperatures.

    nd Cu2O decreased. This is probably because the proportion ofolatilized boron reduces as the BCB content increases and the0 0 1) plane forms. Thus, the crystallization of BCB increases andhe crystallization of CuO and Cu2O decreases. However, due tohe part dissolution of BCB, the amount of crystalline BCB is toomall to be detected when the concentration of BCB is low. As theontent of BCB increased to 5.0 mol%, the second phase of BCB wasetected as shown in Fig. 2 [17].

    The lattice parameter of MST + x BCB ceramics with.0 x 5.0 mol% are calculated and shown in Fig. 3. The lat-ice parameter decreased slightly at first and then increased. Theariation of lattice parameter is identical to the peak shift shown inhe inset of Fig. 2. The decrease of lattice parameter at x = 1.0 mol%s due to the substitution of Cu2+ into Ti4+ sites. Although the ionicadius of Cu2+ (0.73 A, coordination number, CN = 6) is larger thanhat of Ti4+ (0.61 A, CN = 6), the substitution of Cu2+ into Ti4+ sitesreates lattice strain and oxygen vacancies, which decrease theattice parameter a. Lee et al. [18,19] also observed the decreasedattice parameter in Ba0.6Sr0.4TiO3-CuO ceramics. Since the ionicadius of Ba2+ (1.61 A, CN = 12) is larger than that of Sr2+ (1.44 A,N = 12), the incorporation of Ba2+ enlarges the cell volume. Hence,he subsequent increase of lattice parameter reveals the increasingmount of incorporated Ba2+ ions with the increase of BCB content.oreover, the Cu2+ ions cannot incorporate into Sr2+/Ba2+ sites

    CN = 12) due to the small ionic radius of Cu2+. Babu et al. [19]eported that in BaTiO3 ceramics, the Cu2+ cannot be incorporatednto Ba2+ sites.

    The dielectric constant as a function of BCB content is also givenn Fig. 3. Generally, dielectric constant of ceramics is affected byhe presence of the second phases, the modification of the mainrystalline phase and the variation of relative densities. The dif-erence of relative densities between the samples in this study isuite small (

  • 1512 L. Li et al. / Materials Science and Engineering B 178 (2013) 1509 1514

    F theird



    ig. 4. SEM photographs of MST + x BCB ceramics with 0.0 x 5.0 mol% sintered atoped.

    .0 mol% BCB doped. The energy densities are calculated from CVoops by Eq. (1). As the dielectric constants of all the compositions

    re similar, the curves for energy density of all the compositionsre quite close to each other. Hence, we just listed the chargednergy densities and discharged energy densities at the average

    ig. 5. Weibull plots of the BDS data obtained for samples with different content ofCB.

    optimal temperatures, and the EDS element mapping of sample with 1.0 mol% BCB

    Eb of all the compositions in Table 1. Owing to the improvementin average Eb, the sample with 1.0 mol% BCB doped possesses

    the largest energy density (UDischarged, UD = 1.05046 J/cm3), whichis larger than that of the undoped sample (UD = 0.90598 J/cm3).And due to the deterioration of average Eb and the electric field

    Fig. 6. Variations of average Eb and insulation resistivity of MST + x BCB ceramicswith 0.0 x 5.0 mol% sintered at their optimal temperatures.

  • L. Li et al. / Materials Science and Engineering B 178 (2013) 1509 1514 1513




    Table 1The charged and discharged energy densities of all the compositions at their averageEb.

    Samples Charged energydensity (J/cm3)

    Discharged energydensity (J/cm3)

    Undoped 0.91821 0.905981.0 mol% 1.06289 1.050462.0 mol% 0.72525 0.71166

    ig. 7. CV loops of MST + x BCB ceramics with 0.0 x 5.0 mol% sintered at theirptimal temperatures.

    ependence, the 5.0 mol% BCB doped sample has the lowest energyensity (UD = 0.33398 J/cm3).

    The energy efficiencies is defined by [1]

    = UDUC

    100% (7)

    ig. 8. Energy density a) for charged process and b) for discharged process calculatedrom CV loops of sample with 1.0 mol% BCB.








    3.0 mol% 0.56383 0.544435.0 mol% 0.34166 0.33398

    where UD is the discharged energy density and UC is the chargedenergy density. For the sample with 1.0 mol% BCB doped, the energyefficiency is 98.83% at its average Eb (28.78 kV/mm), which is asatisfactory value.

    4. Conclusion

    The multi-ions doped SrTiO3 ceramics with BaCu(B2O5) addi-tive were synthesized and the dielectric properties and energydensities were investigated. The addition of a small amount ofBCB (5.0 mol%) decreased the sintering temperature effectivelyfrom 1300 C to 1075 C. The dielectric constant remained almostunchanged when the SrTiO3 system was doped with 1.0 mol% BCBand then increased with increasing BCB content, which is owingto two opposite effects caused by the formation of second phasesand the dissolution of Cu2+ and Ba2+, respectively. The breakdownstrength of the 1.0 mol% BCB doped sample was improved withthe presence of smaller grains and more homogeneous microstruc-ture. With the further increase in the amount of BCB, the BDSdecreased as the grain size increased and the insulation resis-tivity decreased. Owing to the improvement in average Eb, the1.0 mol% BCB doped sample had the largest energy density in thispaper. The MST ceramic system doped with 1.0 mol% BCB sinteredat 1075 C possesses excellent dielectric properties: r = 311.37,average Eb = 28.78 kV/mm, UD = 1.05 J/cm3 and = 98.83%. Theseproperties indicate that BaCu(B2O5) is a promising sintering addi-tive for SrTiO3-based ceramics, which is widely used in energystorage applications.


    [1] S. Tong, B.H. Ma, M. Narayanan, S.S. Liu, R. Koritala, Appl. Mater. Interfaces 5(2013) 14741480.

    [2] G.X. Dong, S.W. Ma, J. Du, J.D. Cui, Ceram. Int. 35 (2009) 20692075.[3] G.R. Love, J. Am. Ceram. Soc. 73 (1990) 323328.[4] Y. Zhang, J.J. Huang, T. Ma, X.R. Wang, C.S. Deng, X.M. Dai, J. Am. Ceram. Soc. 94

    (2011) 18051810.[5] I. Burn, D.M. Smyth, J. Mater. Sci. 7 (1972) 339343.[6] R.V. Shende, D.S. Krueger, G.A. Rossetti Jr., S.J. Lombardo, J. Am. Ceram. Soc. 84

    (2001) 16481650.[7] Z.Y. Shen, Q.G. Hu, Y.M. Li, Z.M. Wang, W.Q. Luo, Y. Hong, Z.X. Xie, R.H. Liao, J.

    Mater. Sci. Mater. Electron. 24 (2013) 30893094.[8] Z.Y. Shen, W.Q. Luo, Y.M. Li, Q.G. Hu, Z.M. Wang, X.Y. Gu, J. Mater. Sci. Mater.

    Electron. 24 (2013) 607612.[9] Z.Y. Shen, Q.G. Hu, Y.M. Li, Z.M. Wang, W.Q. Luo, Y. Hong, Z.X. Xie, R.H. Liao, J.

    Am. Ceram. Soc. 96 (2013) 25512555.10] Z.Y. Shen, Y.M. Li, W.Q. Luo, Z.M. Wang, X.Y. Gu, R.H. Liao, J. Mater. Sci. Mater.

    Electron. 24 (2013) 704710.11] Z.H. Wu, M.H. Cao, H.T. Yu, Z.H. Yao, D.B. Luo, H.X. Liu, J.Electroceram. 21 (2008)

    210213.12] Q.M. Zhang, L. Wang, J. Luo, Q. Tang, J. Du, J. Am. Ceram. Soc. 92 (2009)

    18711873.13] Z.Y. Shen, H.X. Liu, Z.H. Wu, Z.H. Yao, M.H. Cao, D.B. Luo, Mater. Sci. Eng. B 136

    (2007) 1114.14] Z.H. Wu, H.X. Liu, M.H. Cao, Z.Y. Shen, Z.H. Yao, H. Hao, D.B. Luo, J. Ceram. Soc.

    Jpn. 116 (2008) 345349.

    15] M.H. Kim, J.B. Lim, J.C. Kim, S. Nahm, J. Am. Ceram. Soc. 89 (2006)

    31243128.16] Z.Z. He, W.D. Cheng, Solid State Commun. 149 (2009) 236238.17] H.T. Jiang, J.W. Zhai, J.J. Zhang, X. Yao, J. Am. Ceram. Soc. 92 (2009)


  • 1 ngine



    514 L. Li et al. / Materials Science and E

    18] Y.C. Lee, L.G. Teoh, Y.Y. Yeh, C.S. Chiang, J. Ceram. Soc. Jpn. 118 (2010)597602.

    19] A.R. Babu, A.V. Prasadarao, J. Mater. Sci. Lett. 16 (1997) 313315.20] E.K. Beauchamp, J. Am. Ceram. Soc. 54 (1971) 484487.21] H.T. Chung, B.C. Shin, H.G. Kim, J. Am. Ceram. Soc. 72 (1989) 327329.



    ering B 178 (2013) 1509 1514

    22] T. Tunkasiri, G. Rujijanagul, J. Mater. Sci. Lett. 15 (1996) 17671769.23] B.C. Shin, H.G. Kim, Ferroelectrics 89 (1989) 8186.24] U.M.S. Costa, V.N. Freire, L.C. Malacarne, R.S. Mendes, S. Picoli Jr., E.A. de Vas-

    concelosc, E.F. da Silva Jr., Physica. A 361 (2006) 209215.25] L.A. Dissado, J. Phys. D Appl. Phys. 23 (1990) 15821591.

    Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage1 Introduction2 Experiment method3 Results and discussions4 ConclusionReferences


View more >