Anion Control in the Ionothermal Synthesis of Coordination Polymers

Ferroelectric and piezoelectric properties of tungsten substituted SrBi 2Ta 2O 9ferroelectric ceramicsIndrani Coondoo *,S.K.Agarwal a ,A.K.Jha ba Superconductivity and Cryogenics Division,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India bDepartment of Applied Physics,Delhi College of Engineering,Bawana Road,Delhi 110042,India1.IntroductionDefects in crystals significantly influence physical and various other properties of materials [1].For instance,as it is well known,doping by other elements leads to significant changes in the electrical properties of silicon.Historically,‘‘defect engineering’’has been developed in the field of semiconducting materials such as compound semiconductors as well as in diamond,Si and Ge [2–4].Subsequently,the concept of defect engineering has been applied to other functional materials,and the significant improve-ment in material properties have been achieved in high transition-temperature superconductors [5],amorphous SiO 2[6],photonic crystals [7]and also in the field of ferroelectrics,such as BaTiO 3,Pb(Ti,Zr)O 3(PZT),etc.[8,9].Various structural and electrical properties of bismuth layer-structured ferroelectrics (BLSF)are also strongly affected on deviation from stoichiometric composi-tions and defects have been recognized as a crucially important factor [10–13].It has been found that in BLSF small changes in chemical composition result in significantly altered dielectric and ferroelectric properties including dielectric constant and remanent polarization.In SrBi 2Ta 2O 9(SBT)and SrBi 2Nb 2O 9(SBN),orthor-hombic structural distortions with non-centrosymmetric spacegroup A 21am cause spontaneous ferroelectric polarization (P s )along a axis [14,15].SBT,a member of the BLSF family,has occupied an important position among the Pb-free ferroelectric memory materials [16–18].Tungsten (W 6+)has recently been investigated as a dopant for bismuth titanates and lanthanum doped bismuth titanates,in which the remanent polarization was observed to enhance when a small amount of Ti 4+was substituted by W 6+[19,20].With the objective to improve structural,dielectric and ferroelectric proper-ties,the hexavalent tungsten (W 6+)was chosen as a donor cation for partial replacement of the pentavalent tantalum (Ta 5+)SBT.In this report,the effect of tungsten substitution in SBT (SBTW),on the microstructural,ferroelectric and piezoelectric properties is reported.The results including the improvement in polarization properties have been discussed.2.ExperimentalSamples of compositions SrBi 2(W x Ta 1Àx )2O 9(SBWT),with x =0.0,0.025,0.050,0.075,0.10and 0.20were synthesized by solid-state reaction method taking SrCO 3,Bi 2O 3,Ta 2O 5and WO 3(all from Aldrich)in their stoichiometric proportions.The powder mixtures were thoroughly ground and passed through sieve of appropriate size and then calcined at 9008C in air for 2h.The calcined mixtures were ground and admixed with about 1–1.5wt%polyvinyl alcohol (Aldrich)as a binder and then pressed at $300MPa into disk shaped pellets.The pellets were sintered at 12008C for 2h in air.Materials Research Bulletin 44(2009)1288–1292A R T I C L E I N F O Article history:Received 3October 2008Received in revised form 5December 2008Accepted 6January 2009Available online 15January 2009Keywords:A.CeramicsC.X-ray diffractionD.FerroelectricityA B S T R A C TTungsten substituted samples of compositions SrBi 2(W x Ta 1Àx )2O 9(x =0.0,0.025,0.050,0.075,0.10and 0.20)were synthesized by solid-state reaction method and studied for their microstructural,electrical conductivity,ferroelectric and piezoelectric properties.The X-ray diffractograms confirm the formation of single phase layered perovskite structure in the samples with x up to 0.05.The temperaturedependence of dc conductivity vis-a`-vis tungsten content shows a decrease in conductivity,which is attributed to the suppression of oxygen vacancies.The ferroelectric and piezoelectric studies of the W-substituted SBT ceramics show that the remanent polarization and d 33values increases with increasing concentration of tungsten up to x 0.05.Such compositions with low conductivity and high P r values should be excellent materials for highly stable ferroelectric memory devices.ß2009Elsevier Ltd.All rights reserved.*Corresponding author.Present address:Liquid Crystal Group,National Physical Laboratory,Dr K.S.Krishnan Road,New Delhi 110012,India.Tel.:+919810361727;fax:+911125170387.E-mail address:indrani_coondoo@ (I.Coondoo).Contents lists available at ScienceDirectMaterials Research Bulletinj o ur n a l h o m e p a g e :w w w.e l se v i e r.c om /l oc a t e /m a t r e sb u0025-5408/$–see front matter ß2009Elsevier Ltd.All rights reserved.doi:10.1016/j.materresbull.2009.01.001X-ray diffractograms of the sintered samples were recorded using a Bruker diffractometer in the range 108 2u 708with CuK a radiation.The sintered pellets were polished to a thickness of 1mm and coated with silver paste on both sides for use as electrodes and cured at 5508C for half an hour.Electrical conductivity was performed using Keithley’s 6517A Electrometer.The polarization–electric field (P –E )hysteresis measurements were done at room temperature using an automatic P –E loop tracer based on Sawyer–Tower circuit.Piezoelectric charge co-efficient d 33was measured using a Berlincourt d 33meter after poling the samples in silicone–oil bath at 2008C for half an hour under a dc electric field of 60–70kV/cm.3.Results and discussion3.1.Structural and micro-structural studiesThe phase formation and crystal structure of the ceramics were examined by X-ray diffraction (XRD),which is shown in Fig.1.The XRD patterns of the samples show the characteristic peaks of SBT.The peaks have been indexed with the help of a computer program–POWDIN [21]and the refined lattice parameters are given in Table 1.It is observed that a single phase layered perovskite structure is maintained in the range 0.0 x 0.05.Owing to the same co-ordination number i.e.6and the smallerionic radius of W (0.60A˚)in comparison to Ta (0.64A ˚),there is a high possibility of tungsten occupying the tantalum site.The observance of unidentified peak of very low intensity in the compositions with x >0.05indicates the solubility limit of W concentration in SBT.The unidentified peak is possibly due to tungsten not occupying the Ta sites in the structure as the intensity of this peak is observed to increase with tungsten content.Composition and sintering temperature influences the micro-structure such as grain growth and densification of the specimen,which in turn control other properties of the material [11,13].The effects of W substitution on the microstructure have been examined by SEM and the obtained micrographs are shown in Fig.2.It shows the microstructure of the fractured surface of the studied samples.It is clearly observed that W substitution has pronounced effect on the average grain size and homogeneity of the grains.Randomly oriented and anisotropic plate-like grains are observed in all the samples.It is also observed that the average grain size increases gradually with increasing W content.The average grain size in the sample with x =0.0is $2–3m m while that in the sample with x =0.20the size increases to $5–7m m.3.2.Electrical studiesThe electrical conductivity of ceramic materials encompasses a wide range of values.In insulators,the defects w.r.t.the perfect crystalline structure act as charge carriers and the consideration of charge transport leads necessarily to the consideration of point defects and their migration [22].Many mechanisms were put forward to explain the conductivity mechanism in ceramics.Most of them are approximately divided into three groups:electronic conduction,oxygen vacancies ionic conduction,and ionic and p-type mixed conduction [22].Intrinsic conductivity results from the movement of the component ions,whereas conduction resulting from the impurity ions present in the lattice is known as extrinsic conductivity.At low temperature region (ferroelectric phase),the conduction is dominated by the extrinsic conduction,whereas the conduction at the high-temperature paraelectric phase ($300–7008C)is dominated by the intrinsic ionic conduction [23,25].Fig.3shows the temperature dependence of dc conductivity (s dc )for the undoped and doped SBT samples.The curves show that the conductivity increases with temperature.This is indicative of negative temperature coefficient of resistance (NTCR)behavior,a characteristic of dielectrics [22].It is observed in Fig.3that throughout the temperature range,the dc conductivity of the doped samples are nearly two to three orders lower than that of the undoped sample.Two predominant conduction mechanisms indicated by slope changes in the two different temperature regions are observed in Fig.3.Such changes in the slope in the vicinity of the ferro-paraelectric transition region have been observed in other ferroelectric materials as well [23,24].In addition,it is also observed (Table 2)that the activation energy calculated using the Arrhenius equation [22]in the paraelectric phase increase from $0.80eV for the undoped sample to $2eV for the doped samples.The X-ray photoemission spectroscopic study has confirmed that when Bi 2O 3evaporates during high-temperature processing,vacancy complexes are formed in the (Bi 2O 2)2+layers [26].As a result,defective (Bi 2O 2)2+layers are inherently present in SBT.The undoped SBT shows n-type conductivity,since when oxygen vacancies are created,it leaves behind two trapped electrons [27]:O o !12O 2"þV o þ2e 0(1)where O o is an oxygen ion on an oxygen site,V o is a oxygen vacant site and e 0represents electron.The conductivity in the perovskites can be described as an ordered diffusion of oxygen vacancies [28].Their motion is manifested by enhanced ionic conductivity associated with an activation energy value of $1eV [26].These oxygen vacancies can be suppressed by addition of donors,since the donor oxide contains more oxygen per cation than the host oxide it replaces [29].It has been reported that conductivity in Bi 4Ti 3O 12(BIT)can be significantly decreased,up to three orders of magnitude with the addition of donors,such as Nb 5+and Ta 5+at the Ti 4+sites [23,30].A few other studies on layered perovskites have also reported a decrease inconductivityFig.1.XRD patterns of SrBi 2(W x Ta 1Àx )2O 9samples sintered at 12008C.Table 1Lattice parameters of SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W a (A ˚)b (A ˚)c (A ˚)0.0 5.5212 5.513924.92230.025 5.5214 5.520225.10790.05 5.5217 5.519925.05850.075 5.5191 5.504525.05670.10 5.5142 5.506125.0850.205.51335.493925.0861I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921289with addition of donors [23,24,31].In the present study,the Ta 5+-site substitution by W 6+in SBT can be formulated using a defect chemistry expression as WO 3þV o!Ta 2O 512W Ta þ3O o (2)It shows that the oxygen vacancies are reduced upon the substitution of donor W 6+ions for Ta 5+ions.Hence,it is reasonable to believe that the conductivity in SBT is suppressed by donor addition.As per the above discussion,the high s dc observed in the undoped SBT (Fig.3)can be attributed to the motion of oxygen vacancies.As already discussed,the doped samples show reduced conductivity because the transport phenomena involving oxygen vacancies are greatly reduced.The high E a value of $1.75–2eVcorresponding to the high-temperature region in the doped ceramics is consistent with the fact that in the donor-doped materials,the ionic conduction reduces [32].The activation energy E a in the low temperature ferroelectric region (Table 2)corre-sponds to extrinsic conduction.At lower temperatures the extrinsic conductivity results from the migration of impurity ions in the lattice.Some of these impurities may also be associated with lattice defects.Pure SBT has large number of Schottky defects (oxygen vacancies)in addition to impurity ions whereas in the doped samples,due to charge neutrality,there is relatively less content of oxygen vacancies.Thus,in the doped samples the conductivity in the low temperature region is largely due to the impurity ions only.This explains the high activation energy in pure SBT in the low temperature region compared to doped samples (Table 2).In the high-temperature region,the value of E a in the doped samples is observed to increase with W concentration up to x =0.05but beyond that,it decreases (Table 2).The decrease in the activation energy for samples with x >0.05suggests an increase in the concentration of mobile charge carriers [33].This observation can be ascribed to the existence of multiple valence states of tungsten.Since tungsten is a transitional metal element,the valence state of W ions in a solid solution most likely varies from W 6+to W 4+depending on the surrounding chemical environment [34].When W 4+are substituted for the Ta 5+sites,oxygen vacancies would be created,i.e.one oxygen vacancy would be created for every two tetravalent W ions entering the crystal structure,whichFig.3.Variation of dc conductivity with temperature in SrBi 2(W x Ta 1Àx )2O 9samples.Fig.2.SEM micrographs of fractured surfaces of SrBi 2(W x Ta 1Àx )2O 9samples with (a)x =0.0,(b)x =0.025,(c)x =0.050,(d)x =0.075,(e)x =0.10and (f)x =0.20Table 2Activation energy (E a )in the high-temperature paraelectric region and low temperature ferroelectric region;Curie temperature (T c )in SrBi 2(W x Ta 1Àx )2O 9samples.Concentration of W E a (high temp.)(eV)E a (low temp.)(eV)T c (8C)0.00.790.893110.025 1.920.593080.05 1.960.543250.075 1.940.543380.10 1.860.573680.201.740.54390I.Coondoo et al./Materials Research Bulletin 44(2009)1288–12921290explains the increase in the concentration of mobile charge carriers which ultimately results in an decrease in the E a beyond x>0.05. Hence it is reasonable to conclude that W ions in the SBWT exists as a varying valency state,i.e.at lower doping concentration they exist in hexavalent state(W6+)and at a higher doping concentra-tion,they tend to exist in lower valency states[8].The P–E loops of SrBi2(Ta1Àx W x)2O9are shown in Fig.4.It is observed that W-doping results in formation of well-defined hysteresis loops.Fig.5shows the compositional dependence of remanent polarization(2P r)and the coercivefield(2E c)of SrBi2(Ta1Àx W x)2O9samples.Both the parameters depend on W content of the samples.It is observed that2P rfirst increases with x and then decreases while2E cfirst decreases with x and then increases(Fig.5).The optimum tungsten content for maximum2P r ($25m C/cm2)is observed to be x=0.075.It is known that ferroelectric properties are affected by compositional modification,microstructural variation and lattice defects like oxygen vacancies[10,35,36].In hard ferroelectrics, with lower valent substituents,the associated oxide vacancies are likely to assemble in the vicinity of domain walls[37,38].These domains are locked by the defects and their polarization switching is difficult,leading to an increase in E c and decrease in P r[38]. On the other hand,in soft ferroelectrics,with higher valent substituents,the defects are cation vacancies whose generation in the structure generally increases P r.Similar observations have been made in many reports[38–41].Watanabe et al.[42]reported a remarkable improvement in ferroelectric properties in the Bi4Ti3O12ceramic by adding higher valent cation,V5+at the Ti4+ site.It has also been reported that cation vacancies generated by donor doping make domain motion easier and enhance the ferroelectric properties[43].Further,it is known that domain walls are relatively free in large grains and are inhibited in their movement as the grain size decreases[44].In the larger grains, domain motion is easier which results in larger P r.Also for the SBT-based system,it is known that with increase in the grain size the remanent polarization also increases[45,46].Based on the obtained results and above discussion,it can be understood that in the undoped SBT,the oxygen vacancies assemble at sites near domain boundaries leading to a strong domain pinning.Hence,as observed,well-saturated P–E loop for pure SBT is not obtained.But in the doped samples,the suppression of the oxygen vacancies reduces the pinning effect on the domain walls,leading to enhanced remanent polarization and lower coercivefield.Also,the increase in grain size in tungsten added SBT,as observed in SEM micrographs(Fig.2)contribute to the increase in polarization values.In the present study,the grain size is observed to increase with increasing W concentration.However, the2P r values do not monotonously increase and neither the E c decreases continuously with increasing W concentration(Fig.5). The variation of P r and E c beyond x>0.05,seems possibly affected by the presence of secondary phases(observed in XRD diffracto-grams),which hampers the switching process of polarization [47–50].Also,beyond x>0.05the increase in the number of charge carriers in the form of oxygen vacancies leads to pinning of domain walls and thus a reduction in the values of P r and increase in E c is observed.Fig.6shows the variation of piezoelectric charge coefficient d33 with x in the SrBi2(Ta1Àx W x)2O9.The d33values increases with increase in W content up to x=0.05.A decrease in d33values is observed in the samples with x!0.075.The piezoelectric coefficient,d33,increases from13pC/N in the sample with x=0.0to23pC/N in the sample with x=0.05.It is known that the major drawback of SBT is its relatively higher conductivity,which hinders proper poling[51].High resistivity is therefore important for maintenance of poling efficiency at high-temperature[52,53].The W-doped SBT samples show an electrical conductivity value up to three orders of magnitude lower than that of undoped sample(Fig.3).The positional variation of2P r and2E c in SrBi2(W x Ta1Àx)2O9samples.Fig.6.Variation of d33in SrBi2(W x Ta1Àx)2O9samples.Fig. 4.P–E hysteresis loops in SrBi2(W x Ta1Àx)2O9samples recorded at roomtemperature.I.Coondoo et al./Materials Research Bulletin44(2009)1288–12921291decrease in conductivity upon donor doping improve the poling efficiency resulting in the observed higher d33values.Moreover, since the grain size increases with W content in SBT,it is reasonable to believe that the increase in grain size will also contribute to the increase in d33values[54].The decrease in the value of d33for samples with x!0.075is possibly due to the presence of secondary phases as observed in diffractograms[1,51,55]and the increase in oxygen vacancies for samples with x>0.05.4.ConclusionsX-ray diffractograms of the samples reveal that the single phase layered perovskite structure is maintained in the samples with tungsten content x0.05.SEM micrographs reveal that the average grain size increases with increase in W concentration. The temperature dependence of the electrical conductivity shows that tungsten doping results in the decrease of conductivity by up to three order of magnitude compared to W free SBT.All the tungsten-doped ceramics have higher2P r than that of the undoped sample.The maximum2P r($25m C/cm2)is obtained in the composition with x=0.075.The reduced conductivity allows high-temperature poling of the doped samples.Such compositions with low loss and high P r values should be excellent materials for highly stable ferroelectric memory devices.The d33value is observed to increase with increasing W content up to x0.05.The value of d33 in the composition with x=0.05is$23pC/N as compared to$13 pC/N in the undoped sample.AcknowledgmentsThe authors sincerely thank Prof.P.B.Sharma,Dean,Delhi College of Engineering,India for his generous support and providing ample research infrastructure to carry out the research work.The authors are thankful to Dr.S.K.Singhal,Scientist, National Physical Laboratory,India for his fruitful discussion and suggestions.References[1]Y.Noguchi,M.Miyayama,K.Oikawa,T.Kamiyama,M.Osada,M.Kakihana,Jpn.J.Appl.Phys.41(2002)7062.[2]A.Bonaparta,P.Giannozzi,Phys.Rev.Lett.84(2000)3923.[3]S.Connell,E.Siderashaddad,K.Bharuthram,C.Smallman,J.Sellschop,M.Bos-senger,Nucl.Instrum.Methods B85(1994)508.[4]T.Derry,R.Spits,J.Sellschop,Mater.Sci.Bull.11(1992)249.[5]K.Salama,D.F.Lee,Supercond.Sci.Technol.7(1994)177.[6]H.Hosono,Y.Ikuta,T.Kinoshita,M.Hirano,Phys.Rev.Lett.87(2001)175501.[7]S.Noda,A.Chutinan,M.Imada,Nature407(1999)608.[8]S.Shannigrahi,K.Yao,Appl.Phys.Lett.86(2005)092901.[9]G.H.Heartling,nd,J.Am.Ceram.Soc.54(1971)1.[10]H.Watanabe,T.Mihara,H.Yoshimori,C.A.Paz De Araujo,Jpn.J.Appl.Phys.34(1995)5240.[11]T.Atsuki,N.Soyama,T.Yonezawa,K.Ogi,Jpn.J.Appl.Phys.34(1995)5096.[12]T.Noguchi,T.Hase,Y.Miyasaka,Jpn.J.Appl.Phys.35(1996)4900.[13]M.Noda,Y.Matsumuro,H.Sugiyama,M.Okuyama,Jpn.J.Appl.Phys.38(1999)2275.[14]R.E.Newnham,R.W.Wolfe,R.S.Horsey,F.A.D.Colon,M.I.Kay,Mater.Res.Bull.8(1973)1183.[15]A.D.Rae,J.G.Thompson,R.L.Withers,Acta Crystallogr.Sect.B:Struct.Sci.48(1992)418.[16]H.M.Tsai,P.Lin,T.Y.Tseng,J.Appl.Phys.85(1999)1095.[17]Y.Shimakawa,Y.Kubo,Y.Nakagawa,T.Kamiyama,H.Asano,F.Izumi,Appl.Phys.Lett.74(1999)1904.[18]Y.Noguchi,M.Miyayama,T.Kudo,Phys.Rev.B63(2001)214102.[19]J.K.Kim,T.K.Song,S.S.Kim,J.Kim,Mater.Lett.57(2002)964.[20]W.T.Lin,T.W.Chiu,H.H.Yu,J.L.Lin,S.Lin,J.Vac.Sci.Technol.A21(2003)787.[21]Wu E.,POWD,An interactive powder diffraction data interpretation and indexingprogram Ver2.1,School of Physical Science,Flinders University of South Australia, Bedford Park,S.A.JO42AU.[22]R.C.Buchanan,Ceramic Materials for Electronics:Processing,Properties andApplications,Marcel Dekker Inc.,New York,1998.[23]H.S.Shulman,M.Testorf,D.Damjanovic,N.Setter,J.Am.Ceram.Soc.79(1996)3124.[24]M.M.Kumar,Z.G.Ye,J.Appl.Phys.90(2001)934.[25]Y.Wu,G.Z.Cao,J.Mater.Res.15(2000)1583.[26]B.H.Park,S.J.Hyun,S.D.Bu,T.W.Noh,J.Lee,H.D.Kim,T.H.Kim,W.Jo,Appl.Phys.Lett.74(1999)1907.[27]C.A.Palanduz,D.M.Smyth,J.Eur.Ceram.Soc.19(1999)731.[28]C.R.A.Catlow,Superionic Solids&Solid Electrolytes,Academic Press,New York,1989.[29]M.V.Raymond,D.M.Symth,J.Phys.Chem.Solids57(1996)1507.[30]S.S.Lopatin,T.G.Lupriko,T.L.Vasiltsova,N.I.Basenko,J.M.Berlizev,Inorg.Mater.24(1988)1328.[31]M.Villegas,A.C.Caballero,C.Moure,P.Duran,J.F.Fernandez,J.Eur.Ceram.Soc.19(1999)1183.[32]Y.Wu,G.Z.Cao,J.Mater.Sci.Lett.19(2000)267.[33]B.H.Venkataraman,K.B.R.Varma,J.Phys.Chem.Solids66(2005)1640.[34]C.D.Wagner,W.M.Riggs,L.E.Davis,F.J.Moulder,Handbook of X-ray Photoelec-tron Spectroscopy,Perkin Elmer Corp.,Chapman&Hall,1990.[35]Y.Noguchi,I.Miwa,Y.Goshima,M.Miyayama,Jpn.J.Appl.Phys.39(2000)1259.[36]M.Yamaguchi,T.Nagamoto,O.Omoto,Thin Solid Films300(1997)299.[37]W.Wang,J.Zhu,X.Y.Mao,X.B.Chen,Mater.Res.Bull.42(2007)274.[38]T.Friessnegg,S.Aggarwal,R.Ramesh,B.Nielsen,E.H.Poindexter,D.J.Keeble,Appl.Phys.Lett.77(2000)127.[39]Y.Noguchi,M.Miyayama,Appl.Phys.Lett.78(2001)1903.[40]Y.Noguchi,I.Miwa,Y.Goshima,M.Miyayama,Jpn.J.Appl.Phys.39(2000)L1259.[41]B.H.Park,B.S.Kang,S.D.Bu,T.W.Noh,L.Lee,W.Joe,Nature(London)401(1999)682.[42]T.Watanabe,H.Funakubo,M.Osada,Y.Noguchi,M.Miyayama,Appl.Phys.Lett.80(2002)100.[43]S.Takahashi,M.Takahashi,Jpn.J.Appl.Phys.11(1972)31.[44]R.R.Das,P.Bhattacharya,W.Perez,R.S.Katiyar,Ceram.Int.30(2004)1175.[45]S.B.Desu,P.C.Joshi,X.Zhang,S.O.Ryu,Appl.Phys.Lett.71(1997)1041.[46]M.Nagata,D.P.Vijay,X.Zhang,S.B.Desu,Phys.Stat.Sol.(a)157(1996)75.[47]J.J.Shyu,C.C.Lee,J.Eur.Ceram.Soc.23(2003)1167.[48]I.Coondoo,A.K.Jha,S.K.Agarwal,Ferroelectrics326(2007)35.[49]T.Sakai,T.Watanabe,M.Osada,M.Kakihana,Y.Noguchi,M.Miyayama,H.Funakubo,Jpn.J.Appl.Phys.42(2003)2850.[50]C.H.Lu,C.Y.Wen,Mater.Lett.38(1999)278.[51]R.Jain,V.Gupta,A.Mansingh,K.Sreenivas,Mater.Sci.Eng.B112(2004)54.[52]I.S.Yi,M.Miyayama,Jpn.J.Appl.Phys.36(1997)L1321.[53]A.J.Moulson,J.M.Herbert,Electroceramics:Materials,Properties,Applications,Chapman&Hall,London,1990.[54]H.T.Martirena,J.C.Burfoot,J.Phys.C:Solid State Phys.7(1974)3162.[55]R.Jain,A.K.S.Chauhan,V.Gupta,K.Sreenivas,J.Appl.Phys.97(2005)124101.I.Coondoo et al./Materials Research Bulletin44(2009)1288–1292 1292。

二维网状配位聚合物［Co(NDC)(bpp)(H2O)］n的合成作者：周永红汤乔雅张茜苗体方来源：《牡丹江师范学院学报（自然科学版）》2018年第04期摘要：; 以1，4-萘二酸（H2NDC）和1，3-二（4-吡啶基）丙烷（bpp）为配体，在水热条件下合成新型配位聚合物[Co（NDC）（bpp）（H2O）]n （1）.单晶结构分析表明：合成的配合物属单斜晶系，P21/n空间群，晶胞参数：a = 1.204 3（2） nm，b = 1.311 1（3） nm，c = 1.421 55（12） nm，β = 103.113（19） °，V = 2.185 9（6） nm3.配合物中Co（II）与来自于两个1，4-萘二酸根的三个O原子、两个1，3-二（4-吡啶基）丙烷的两个N原子以及一个水分子的O原子配位，处于变形八面体环境中.Co（II）经NDC2-桥连形成一维链状结构，链与链之间通过bpp桥连形成二维网状结构.关键词：钴配合物;1，4-萘二酸; 晶体结构[中图分类号]O614.7 ;;;[文献标志码]Synthesis of Two-dimensional Network Coordination Polymer [Co（NDC）（bpp）（H2O）]nZHOU Yong-hong ， TANG Qiao-ya ， ZHANG Qian， MIAN Ti-fang（School of Chemistry and Material Science，Huaibei Normal University; Huaibei 235000，China）Abstract： One novel Co（II） coordination polymer， [Co（NDC）（bpp）（H2O）]n （1）（H2NDC = 1，4-naphthalenedicarboxylic acid， bpp = 1，3-bis（4-pyridyl）propane）was synthesized by hydrothermal method with 1，4-naphthalenedicarboxylic acid and 1，3-bis（4-pyridyl）propane as ligands. The single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in monoclinic， space group P21/n with a = 1.204 3（2） nm，b = 1.3111（3） nm，c = 1.421 55（12） nm，β = 103.113（19） °，and V = 2.185 9（6） nm3. The Co（II） ion is six coordinated with distorted octahedral coordination geometry by three oxygen atoms from two NDC2- anions， two nitrogen atoms of two bpp ligands and one oxygen from water molecule. In 1， the adjacent Co（II） ions are bridged by NDC2- anions to form one dimensional chain. Furthermore，the chains are linked by bpp ligands， resulting in the formation of two-dimensional network.Key words： Cobalt（II） complex; 1，4-naphthalenedicarboxylic acid; crystal structure通過分子自组装构筑具有特殊功能和丰富拓扑结构的配位聚合物已成为配位化学、超分子化学、材料化学和晶体化学领域的研究热点.[1]在含N配体的辅助下，有机多羧酸可表现出灵活多变的配位模式，与金属离子配位可形成从一维到三维的配位聚合物.[2]1，4-萘二酸是合成染料中间体和荧光增白剂的原料，具有多个配位点，可以采用单齿、双齿、桥连等模式与金属离子配位，因而被广泛应用于金属配位聚合物的合成.[3]笔者以1，4-萘二酸和1，3-二（4-吡啶基）丙烷为配体与Co（II）离子反应，得到一个结构新颖的配位聚合物[Co（NDC）（bpp）（H2O）]n （1）.1 实验部分1.1 仪器与试剂德国艾力蒙塔公司Vario EL III元素分析仪，美国赛默飞世尔公司Nicolet 170sx FT-IR型红外光谱仪，德国布鲁克公司Bruker SMART APEX CCD型单晶X射线衍射仪，岛津公司DTG-60H热重分析仪.所使用的化学试剂均为分析纯.1.2 [Co（NDC）（bpp）（H2O）]n（1）配合物的合成在含Co（CH3COO）2·4H2O （0.024 9 g， 0.1 mmol）的10 mL水溶液中加入1，4-萘二酸（0.021 6 g， 0.1 mmol）和1，3-二（4-吡啶基）丙烷（0.019 8 g， 0.1 mmol）.室温搅拌30 min后，将此混合物移入容积为23 mL的高压反应釜中.密闭置于120 ℃烘箱中反应72 h后，自然冷却至室温.底部得到粉红色块状晶体，挑出适于X 射线衍射分析的单晶，产率约53%.元素分析结果 [实验值（计算值）%]：C 61.27 （61.30），H 4.53 （4.50），N 5.76 （5.72）.IR （KBr， cm-1）： 3 117 s， 1 611 vs， 1 526 s， 1 445 w， 1 389 s， 1 308 w， 1 155 m， 979 m， 785 m， 670 m， 503 m.1.3 晶体结构测定将尺寸为0.29 mm × 0.27 mm × 0.22 mm 的粉红色配合物块状晶体置于X射线单晶衍射仪上，在296 K下用经石墨单色化的Mo Kα 射线（λ=0.071 073 nm）作为辐射源，以SymboljA@-ω扫描方式在2.00<θ<25.00°范围内共收集10 353个衍射点，其中独立衍射数据3 800个（Rint=0.078 3）.所有非氢原子用直接法解出，并用最小二乘法对结构进行精修.全部计算使用SHELXTL 程序完成.[4]有关晶体学数据见表1.2 结果与讨论2.1 配合物的晶体结构配合物1的分子结构见图1，主要键长和键角见表2.结构分析表明，配合物1具有二维网状结构，其不对称单元包括1个Co（II）离子、1个NDC2-离子、1个bpp分子和1个配位水分子.由图1可见，在配位聚合物1中，每个Co（II）离子与2个bpp分子的2个N原子、2个NDC2-离子的3个氧原子以及1个水分子配位，处于六配位的变形八面体配位环境.O3A，O4A，O1，N2B位于赤道平面，O1W和N1处于轴向位置.O（3A）-Co（1）-O（4A），O （1）-Co（1）-O（4A），O（1）-Co（1）-N（2B）和O（3A）-Co（1）-N（2B）的键角分别为59.87（12）°，105.28（14）°，101.30（16）°和93.67（14）°，总键角为360.12°，表明O3A，O4A，O1，N2B，Co（II）几乎在一个平面上.处于轴向位置的O1W和N1与组成赤道平面原子的键角为82.67（14）°～98.09（16）°，接近90°.配體NDC2-和bpp发挥了桥连作用，连接Co（II）离子形成整体框架.1，4-萘二酸的两个羧基都是脱质子的，分别以单齿、螯合方式配位，桥连相邻的Co（II）离子形成一维链状结构.在此链中，相邻的Co…Co间距为10.720 3 A 。

第 4 期第 183-191 页材料工程Vol.52Apr. 2024Journal of Materials EngineeringNo.4pp.183-191第 52 卷2024 年 4 月两性离子-阴离子双交联P（AAm-co-AAc-co-SBMA-co-AMPS）/Fe3+水凝胶的摩擦学性能研究Tribological properties of zwitterionic-anionicdual-crosslinked P（AAm-co-AAc-co-SBMA-co-AMPS）/Fe3+ hydrogel李子恒1，王斌斌1，尤德强1，李卫1，王小健1，2*（1 暨南大学先进耐磨蚀及功能材料研究院，广州 510632；2 暨南大学韶关研究院，广东韶关 512029）LI　Ziheng1，WANG　Binbin1，YOU　Deqiang1，LI　Wei1，WANG　Xiaojian1，2*（1 Advanced Wear & Corrosion Resistant and Functional Materials，Jinan University，Guangzhou 510632，China；2 Shaoguan ResearchInstitute of Jinan University，Shaoguan 512029，Guangdong，China）摘要：水凝胶是一种理想的软骨修复材料，但目前很难有人工材料能实现软骨的超低摩擦因数。

使用两性离子单体［2-（甲基丙烯酰氧基）乙基］二甲基-（3-磺丙基）（SBMA）和阴离子单体2-丙烯酰氨基-2-甲基丙磺酸（AMPS）合成一种两性离子-阴离子双交联P（AAm-co-AAc-co-SBMA-co-AMPS）/Fe3+水凝胶。

在水和PBS中进行摩擦学测试，以评估两性离子和阴离子基团对摩擦因数（CoF）的影响。

结果表明：SBMA和AMPS引入的物理交联点可以提高水凝胶的抗压强度，在水中实现了较低CoF（0.04）；此外，在PBS中观察到CoF进一步降低至0.015，CoF的降低是由于水凝胶在PBS中浸泡产生的高度水合上层所造成的。

化工进展Chemical Industry and Engineering Progress2024 年第 43 卷第 4 期具有烷基磺酸侧链的凝胶型聚苯并咪唑质子交换膜的制备与表征朱泰忠1，张良1，黄泽权1，罗伶萍1，黄菲1，薛立新1，2（1 浙江工业大学化工学院膜分离与水科学技术中心，浙江 杭州 310014；2温州大学化学与材料工程学院，浙江 温州 325035）摘要：磷酸（PA ）掺杂聚苯并咪唑（PBI ）以其优异的热化学稳定性和高玻璃化转变温度成为高温质子交换膜燃料电池（HT-PEMFCs ）的首选材料。

然而，由于低温下磷酸较弱的解离度和传递速率，导致膜的质子传导性能不佳，电池冷启动困难。

因此，研发可在宽温湿度范围内高效运行的高温质子交换膜成为当前挑战。

特别是拓宽其低温运行窗口、实现冷启动对这类质子交换膜燃料电池在新能源汽车领域的实际应用具有重要意义。

本文通过多聚磷酸溶胶凝胶工艺与内酯开环反应设计并合成了一系列磷酸掺杂的具有柔性烷基磺酸侧链的凝胶型聚苯并咪唑质子交换膜。

重点探究了烷基磺酸的引入以及侧链长度对磷酸掺杂水平、不同温湿度下的质子传导率及稳定性的影响规律。

研究结果表明，所制备的质子交换膜具有凝胶型自组装片层堆叠的多孔结构，有利于吸收大量磷酸并提供质子快速传输通道。

其中，PA/PS-PBI 展现出了在宽温域范围内均优于目前所报道的其他工作的质子传导性能。

特别是常温下，其质子传导率从原膜的0.0286S/cm 提升至0.0694S/cm 。

80℃下，其质子传导率从原膜的0.1117S/cm 提升至0.1619S/cm 。

200℃下，其质子传导率从原膜的0.2609S/cm 提升至0.3578S/cm 。

此外，该膜在80℃和0%相对湿度（RH ）条件下仍可具有与Nafion 膜在100%RH 时相当的质子传导率，为打破质子交换膜经典定义、实现宽温域（25~240℃）运行提供新的方案。