FAN Min LI Guo-Bao WANG Dong-Wei JIN Tou-Nan,*LIAO Fu-Hui LIN Jian-Hua

(1Beijing National Laboratory for Molecular Sciences,State Key Laboratory of Rare Earth Materials Chemistry and Applications,College of Chemistry and Molecular Engineering,Peking University,Beijing 100871,P.R.China;2College of Material Science and Engineering,Beijing University of Technology,Beijing 100022,P.R.China;3National Center for Nanoscience and Technolgy,Beijing 100190,P.R.China)

Synthesis,Structure and Characterization of Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)Solid Solutions

FAN Min2LI Guo-Bao1,*WANG Dong-Wei3JIN Tou-Nan2,*LIAO Fu-Hui1LIN Jian-Hua1,*

(1Beijing National Laboratory for Molecular Sciences,State Key Laboratory of Rare Earth Materials Chemistry and Applications,College of Chemistry and Molecular Engineering,Peking University,Beijing 100871,P.R.China;2College of Material Science and Engineering,Beijing University of Technology,Beijing 100022,P.R.China;3National Center for Nanoscience and Technolgy,Beijing 100190,P.R.China)

Abstract: Solid solutions of Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)were synthesized by a traditional solid state reaction and characterized by powder X-ray diffraction.The solutions crystallize in theP4mmspace group at room temperature.Differential scanning calorimetry(DSC)measurements were performed to obtain phase transition temperatures(Tc)for the samples,and these were found to decrease with an increase in the amount of doped Tb and Mn.The temperature dependent dielectric constant shows a peak close to theTc,indicating that the corresponding phase transition is a ferroelectric phase transition.Magnetic measurements indicate that a paramagnetic to antiferromagnetic phase transition occurs at 25 and 29 K for Pb1-xTbxTi1-xMnxO3withx=0.08 andx=0.10,respectively.

Key Words:Solid-state reaction;PbTiO3;Phase transition;Ferroelectrics;TbMnO3

1 Introduction

The perovskite ferroelectric PbTiO3related materials have been extensively studied for their applications in the field of modern sensors,transducers,ferroelectric random access memories.1-3The properties of PbTiO3are usually modified by doping with other elements.4-16For example,the ferroelectric phase transition of PbTiO3occurs around 490°C from cubic phase(high temperature paraelectric phase)to tetragonal phase(low temperature ferroelectric phase).By doping some ions into the Pb sites and/or Ti sites of PbTiO3,the above phase transition temperature can be modified to meet the needs of certain application.In order to introduce multiferroic to the PbTiO3base materials,several attempts have been made to study the system of PbTiO3-BiFeO317-19because BiFeO3is a well known multiferroic.20Then we focus our attentions on the PbTiO3-TbMnO3system,where TbMnO3is also a well known multiferroic.21Our study shows that it is not easy to get pure phases in PbTiO3-TbMnO3system although hard efforts have been performed for a long time.Here,the synthesis,structure,dielectric and magnetic properties for the(1-x)PbTiO3-xTbMnO3with 0≤x≤0.10,are firstly presented.

2 Experimental

Pb1-xTbxTi1-xMnxO3(x=0,0.02,0.04,0.06,0.08,and 0.10,named as S1,S2,S3,S4,S5,and S6)has been synthesized from stoichiometric amounts of Tb4O7(99.99%),PbO2(A.R.),TiO2(A.R.),and MnCO3(A.R.).The weighted powders were mixed into a paste with acetone using an agate mortar and pestle,dried and heated in Al2O3crucibles at 850°C for 12 h.Finally,the samples were pressed into pellets and heated at 900°C in Al2O3crucibles in an electric muffle furnace for 5 days with several intermediate pressing and grinding steps to make sure that the obtained sample is a single phase confirmed by X-ray diffraction method.The mass of the samples was monitored before and after heat treatments.The maximum difference was about 4 mg for the 6 g samples.Therefore,the compositions of the samples were considered to be the same as the initial ones.

Powder X-ray diffraction(PXRD)data for structure refinement were collected on a Bruker D8 Advance diffractometer with Cu Kα1(λ=0.15407 nm)radiation(2θ range:10°-120°;step:0.0197°;scan speed:10 s·step-1)at 50 kV and 40 mA.The X-ray diffraction data were analyzed using GSAS software.22,23The differential scanning calorimetry(DSC)measurement was carried out on SETARAM DSC131EVO equipment from room temperature(RT)to 600°C in Ar atmosphere with a heating rate of 10 °C·min-1.The dielectric properties of the samples were measured using Precision Impedance Analyzer 65120B(Wayne Kerr Electronics).The magnetic properties were investigated with a Quantum Design physical property measurement system(PPMS)from 2 to 300 K.

3 Results and discussion

3.1 X-ray diffraction analysis

The powder X-ray diffraction patterns of Pb1-xTbxTi1-xMnxO3(x=0.00,0.02,0.04,0.06,0.08,and 0.10)are similar to each other as shown in Fig.1(a).This implies that the structures of this series samples are the same.The structure of PbTiO3was used as the beginning model for the Rietveld refinement of the X-ray diffraction data of these samples.Acceptable fittings between the experimental data and the proposed models are obtained with Rp＜11%,Rwp＜15%(the R factor)for all the data.During the refinement,Pb and Tb atoms are at the sites 4a(0,0,z)for Pb in PbTiO3with an occupancy of(1-x):x,Ti and Mn atoms are at the sites 4b(0.5,0.5,z).Table 1 lists the refinement details of the sample S4(Pb1-xTbxTi1-xMnxO3,x=0.06)as a representative example.The corresponding Rietveld plot is shown in Fig.1(b).Linear relationship between the volume of the unit cell and the value of x in Pb1-xTbxTi1-xMnxO3is found as shown in Fig.1(c),which agrees well with Vigard′s law.24,25Therefore,it can be confirmed that a solid solution Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)forms.

3.2 DSC measurement

Table 1 Refinement details of Pb1-xTbxTi1-xMnxO3(x=0.06)ain space groupP4mm

As mentioned above,a solid solution Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)has been synthesized.They all crystallize in the space groupP4mmat room temperature,which means that a ferroelectric phase transition may occurs above room temperature.As it is well known that the ferroelectric phase transition for PbTiO3is a first order phase transition,which should show thermal effect during the phase transition.Therefore,the DSC measurements can be performed to find the phase transition temperature(Tc)for the samples S1 to S6.Fig.2 shows the corresponding results for these samples.All the samples undergo an endothermic phase transition above room temperature.Apart from the endothermic peak atTc,no other peak/transition occurred in the measured temperature region.For PbTiO3,the present data show that there is an endothermic phase transition occurs atTc=485°C,which is consistent with the reported value26for the ferroelectric phase transition of PbTiO3.Therefore,it is reasonable to assume that the phase transition occurring atTcis a ferroelectric phase transition.When the Tb3+ion is substituted at the A-cation lattice site and the Mn3+ion is substituted at the B-cation lattice site,theTcshifts towards the lower value.It is observed that the gradual increase in the concentration of Tb3+ion at the A-cation site and Mn3+ion at the B-cation site of the host lattice decreases the transition temperature,which is shown in Fig.2.This result is different from the reported data for PbTiO3-BiFeO3system19,where when Bi and Fe are substituted into PbTiO3the ferroelectric phase transition temperature increases.

3.3 Dielectric property

The dielectric property of the samples was measured using Precision Impedance Analyzer 65120B.The temperature dependent dielectric constants and losses of S2 to S6 are shown in Fig.3.There are peaks around the temperature corresponding to Tc,which confirms that the phase transition is a ferroelectric phase transition.The measured dielectric constants of S4 to S6 are comparable to the reported values of other doped PbTiO3,such as in the system(1-x)PbTiO3-xBiAlO3(x=0,0.05,0.10,0.15).27However,the dielectric constants of S2 and S3 are very low,which is attributed to the fact that the samplesare not very compact.The relative density of the samples is just about 0.65 for S2 and S3,and about 0.80 for S4,S5,and S6.In fact,the temperature dependent dielectric constant for PbTiO3is not given in Fig.3 because the pellet usable for dielectric measurement for PbTiO3has not been obtained,which is a known difficulty for the synthesis of PbTiO3.27The dielectric losses of these samples are similar to that reported for other similar system such as BiFeO3doped Bi(MgTi)O3-PbTiO3,18which are little higher than that for practical use.

3.4 Magnetic property

The temperature dependence of the magnetic susceptibility of the samples S2 to S6 measured in a field of 7957 A·m-1(100 Oe)is shown in Fig.4.The departure of the zero-fieldcooled and field-cooled curves for the samples S2 and S6 occurred around 42 K is attributed to the impurity of Mn3O4,28although it is difficult to find the diffraction peaks of Mn3O4in the powder X-ray diffraction patterns of S2 and S6 because the amount of Mn3O4is too less.This departure is not observed for the samples S3,S4,and S5.Therefore,it is reasonable to believe that this departure is not the property of the solid solution Pb1-xTbxTi1-xMnxO3itself.Furthermore,it is reasonable to believe that zero-field-cooled and field-cooled data are overlapped for the solid solution Pb1-xTbxTi1-xMnxO3.No loops are found in the M-H curves of the samples S2 to S6 at 2 and 300 K as shown in Fig.4(f),which confirms the above suggestion.It should be mentioned that in Fig.4(a-e),the value of the vertical axis is 4π×10-6m3per mole of Pb1-xTbxTi1-xMnxO3for each sample,and that for Fig.4(f)is 10-3A·m2per mole of(Tb+Mn).So the curves for the different samples are overlapped as shown in Fig.4(f),no effort is paid to indicate which line corresponding to S2,S3,S4,S5,or S6.

It is found that with the increase of the amount of Tb and Mn doped into PbTiO3,the peak corresponding to the antiferromagnetic ordering appears more clearly.The magnetic phase transition temperature(TN)increases from 25 K for S5 to 29 K for S6.

4 Conclusions

The samples in the system(1-x)PbTiO3-xTbMnO3(0≤x≤0.10)have been synthesized by traditional solid state reaction at 900°C.They form a solid solution with a decrease of the volume of unit cell when more Tb and Mn in the samples.They all crystallize in the space groupP4mm at room temperature.The ferroelectric phase transition temperature(Tc)decreases with the increase of Tb and Mn in the samples.In the meantime,antiferromagnetic ordering is found for the samples Pb1-xTbxTi1-xMnxO3(x=0.08,0.10)indicating that this system is a potential multiferroic.

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Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)固溶體的合成、結(jié)構(gòu)與表征

范 敏2李國寶1,*王東偉3金頭男2,*廖復(fù)輝1林建華1,*

(1北京大學(xué)化學(xué)與分子工程學(xué)院,北京分子科學(xué)國家實(shí)驗(yàn)室,稀土材料化學(xué)及應(yīng)用國家重點(diǎn)實(shí)驗(yàn)室,北京100871;2北京工業(yè)大學(xué)材料科學(xué)與工程學(xué)院,北京100022;3國家納米科學(xué)中心,北京100190)

用固相反應(yīng)合成了Pb1-xTbxTi1-xMnxO3(0≤x≤0.10)固溶體,并用X射線粉末衍射進(jìn)行了表征,室溫下其空間群為P4mm.熱分析儀測(cè)試結(jié)果顯示,隨著Tb和Mn摻雜量的增加,該固溶體的相變溫度Tc降低.介電常數(shù)在Tc附近出現(xiàn)峰值,表明對(duì)應(yīng)的相變是鐵電相變.磁性測(cè)量顯示,當(dāng)x=0.08和x=0.10時(shí),Pb1-xTbxTi1-xMnxO3分別在25和29 K附近有順磁性向反鐵磁性的轉(zhuǎn)變.

固相反應(yīng);PbTiO3;相變;鐵電;TbMnO3

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Received:December 27,2010;Revised:February 15,2011;Published on Web:March 11,2011.

?Corresponding authors.LI Guo-Bao,Email:liguobao@pku.edu.cn.JIN Tou-Nan,Email:tnjinkim@bjut.edu.cn.

LIN Jian-Hua,Email:jhlin@pku.edu.cn.

The project was supported by the National Natural Science Foundation of China(20771008),Scientific Research Key Program of Beijing Municipal Commission of Education,China(KM201010005019),and National Key Basic Research Project of China(2010CB833103).

國家自然科學(xué)基金(20771008),北京市教委重點(diǎn)基金(KM201010005019)和科技部重大研究計(jì)劃(2010CB833103)資助項(xiàng)目