BiFeO3修飾的PZT固溶薄膜中增強的鐵電和介電性質(zhì)_圖文(精)

1、Enhan ced ferroelectric and dielectric properties in BiFeO3 modified PZT solid solution filmsLiu Ho ngri1,2, Liu Zuli1*, Liu Qin g, Li Xin gao, Yao Kailun 11 Departme nt of Physics, Huazh ong Uni versity of Scie nee and Tech no logy, Wuhan, China, (4300742 Department of Physics, Hubei Normal Univers

2、ity, Huangshi, China (435002E-mail :Abstract(PbZr0.5Ti 0.5O 3 x -(BiFeO3 1-x films have bee n prepared on LaNiO3/SiO2/Sisubstrates by sol-gel process at an ann eali ng temperature of 60C. X-ray diffractio npatter ns in dicate that the samples show (110 preferred orie ntati on or ran dom orie ntati o

3、naccord ing to the x and no impure phase was observed for all films. The study offerroelectricity shows that the saturated polarizati ons are enhan ced by the in corporati onof BiFeO3. Remnant polarization of 33.7 C/cm2, 308 C/m2, 34.4 C/cm2 and 37.6 pC/cm2are observed for the films with x=0 to 0.20

4、 .In additi on, dielectric properties were enhan cedthrough the solid soluti on with BiFeO3. Leakage con ducti on was also in creased by the incorporati on of BiFeO 3.Keywords: (PbZr0.5Ti 0.5O 3 1-x -(BiFeO3 x films; sol gel; ferroelectricity; dielectricproperty; leakage curre nt.1. In troducti onIn

5、 rece nt years, exte nsive atte nti on has bee n focused on multiferroic materials, inwhich both electrical and magn etic orderi ng can coexist. They are also called magnetoelectric materials 1 and have many pote ntial applicati ons in in formatio n tech no logy,sen sors, (MEMS devices, and spintron

6、ics devices etc. BiFeO3 (BFO is such material andreported to exhibit magnetic ordering with a relatively high Neel temperature (TN 370 Cand ferroelectric orderi ng with Cure temperature (TC 850 C 2, its atomic structure wasdeterm ined from si ngle crystal and powder x-ray and n eutr on diffraction s

7、tudies, and theresults reveal that BFO has a rhombohedrally distorted perovskite structure with spacegroup R3c 3. A ferroelectric hysteresis loop of BFO sin gle crystal with polarizatio n valuesof 3.5 .1 C/cm2 has bee n con firmed at liquid n itroge n temperature 4.There were works focused on the st

8、udy of solid solutio ns of BFO and other ABO3 typeperovskite ferroelectrics such BaTiO3, PbTiO3 and PbLaZrTiO3 etc al. 5-7. The structural,dielectric, ferroelectric and mag netic properties with the content of BFO have bee n studied.BFO has also bee n used to modify other ferroelectrics such as SrBi

9、2Nb 2O 9 and SrBi2Ta2O 9 and obta in ed en ha need dielectric properties 8, 9. PbZr1-x Ti x O 3 (PZT is classicABO3 type ferroelectrics with large remnant polarizati on and was in ten sively used inmemory device and piezoelectric device. It has bee n deposited on all sorts of substratessuch as Pt/Ti

10、/SiO2/Si, ITO/glass and LaNiO3/Si substrates 10-12. I n general, PZT filmsdeposited on LaNiO3 (LNO bottom electrodes adopted (100 or (001 preferred orientationand has the small remnant polarization than the (111 preferred orie ntati on films onITO/glass or LaNiO3/Si. More over, there were works on t

11、he substitution of PZT on A or Bsite and obtained enhanced ferroelectricity and dielectric properties 13, 14. The incorporati on of BFO with other ABO3 type perovskite ferroelectrics is co-substitution on Aand B sites in essential. Since the incorporation of BiFeO3 with other ferroelectrics canenhan

12、ce the dielectric property, it may be the same to PZT. Further more, there is noreports on the BFO modified PZT films as our knowledge. For the purpose, PZT1-x -BFO xfilms with x=0, 0.05, 0.10 and 0.2 were prepared by sol-gel process on LaNiO3/SiO2/Sisubstrates and the ferroelectric, dielectric and

13、leakage con duct ion properties were studiedin our work.2. Experime nt proceduresThe BiFeO3 precursor solution was prepared usi ng Bi (NO3 35H2O and Fe(NO3 39H2O as staring materials. Bi(NO3 35H2O and Fe(NO3 3 9H2O were mixed with a mol ratioof 1/1 and dissolved at room temperature in 2-methoxyethan

14、ol and stirred for 30 minu tes.Then acetic an hydride was added to dehydrate and etha no lam ine was added to adjustthe viscosity under constant stirring. The stock solution was adjusted to 0.3 M by add ingmethoxyetha nol. The above process was performed in an ambie nt atmosphere at roomtemperature.

15、The Pb(ZrO.5Ti 0.5O 3 precursor solution was prepared usi ng Pb(CH3COO 23H2O,Zr(NO3 4 5H2O and Ti(C4H 9O 4 as staring materials. Pb(CH3COO 23H2O was dissolvedin 2-methoxyetha nol and circumflue nee for 30 minu tes. The n Zr(NO3 4 5H2O and Ti(C4H9O 4 4 were dumped into 2-methoxyethanol and stirred fo

16、r 30 minutes to dissolvedrespectively. The mol ratio of Pb(CH3COO 23H2O, Zr(NO3 4 5H2O and Ti(C4H 9O 4 4were 1.1:0.5:0.5 (10 % Pb excess to compe nsate the Pb loss during the annealing process.Then the above solutions were mixed under constant stirring, ice acetic acid was added tostabilize the solu

17、tion. The concentration was adjust to 0.3 M by add 2-methoxyetha nol.The Pb(Zr0.5Ti 0.5O 3 precursor soluti on and BiFeO3 precursor soluti ons weremixed with proper volume ratio of 1:0, 0.95:0.05 and 0.9:0.10 and 0.80:0.20 to obtain(PZT1-x -BFO x total precursor soluti on. LaNiO3/SiO2/Si was used as

18、 substrates, thepreparati on tech no logy refer to 12. The depositi ons were carried out by spin coat ing at6000 rpm for 20 s. Each deposition layer was pre-annealing at 350C for 3 minutes andcrystallized at 600 C for 3 minutes in air atmosphere. Then the temperature was rapidlydropped to 300 C in 3

19、 minutes. The spin coating was repeated several times to obtain thedesired thick ness.Structure of the films was an alyzed by X-ray diffractio n. The XRD patter ns wererecorded with X-ray diffraction meter with Cu Ka Thtiatioface and crosssecti on morphology areFig. 1 XRD patterns of PZT1-xBF0 x ann

20、 ealed at 600 C.an alyzed by sea nning electric microscopy (AFM and atom force microscopy (SEMrespectively. For electrical measureme nts. Pt dots of 0.01mm2 were deposited through a mask onthe films by sputteri ng. The ferroelectric hysteresis loops and leakage con ducti ons were obta inedusing a pr

21、ecisi on work stati on (Radia nt Tech no logy. Dielectric con sta nt and loss tangent weremeasured with HP 4284A LCR meter.3. Results and discussi onsThe XRD diffraction patterns obta in ed for the PZT1-x BFO x films where x=0.0, 0.05, 0.10,Fig. 2 Cross sectio n SEM photo of pure PZT filmand 0.20 ar

22、e shown in figure 1. All films are well crystallized since the peaks for the (PZT1-x(BFOx phase are sharp and slim. It is easy to see that all films show perovskite structure and noimpure phase such as pyrochlore phase was identified up to x = 0.20. Moreover, only tetrago nalphase (PZT phase can be

23、observed and no rhombohedra phase (BiFeO3 phase was identified inthe whole composition range, therefore solid solution phase was formed in the whole compositioncontent range for all films. The films with x =0 to 0.10 show (110 preferred orientation and the filmwith x = 0.2 show random orientation. I

24、n our work, the LNO bottom electrodes are (100 preferredoriented, while we did not obtain (100 preferred oriented PZT film. The results are different frommost already reported results 15,16, 17, in the above work, pure PZT films adopted (100 preferredorie ntati on on (100 preferred orie nted LaNiO3

25、bottom electrodes because of crystal lattice match.In our work, the (110 preferred orientation of pure PZT is very likely caused by the stress duri ng therapid cooli ng. In additi on, the distorti on of crystallattice by the co-substitution in A site and B site by Bi and Fe respectively may attribut

26、eto the orientation of the films.Figure 2 shows the cross section SEM photo of pure PZT, which indicates that the film has ahomoge neous thick ness. The thick ness, judged from the photo, is about 300 nm.Figure 3 presents the AFM images of PZT1-x BFO x thin films with x = 0.00 to 0.20 ann ealedat 60

27、0 C. Te AFM image shows that the pure PZT film is made of un iform fine grains and the finegrain beg in to growth into larger grains with the in creas ing of x. The film with x = 0.20 has thelargest and even grain. More over, the coarseness of the film is in creased with x. The film with x =0.20 has

28、 the largest surface coarse ness. Therefore the in corporati on of BFO is attributed toenhance the nu cleati on rate and therefore the films with the incorporation of BFO are easier togrow into larger grains.Figure 4 shows the electric hysteresis loops of PZT1-x -BFO x films with x = 0.00to 0.20 ann

29、ealed at 600 C. Thefilms show different saturate polarization (Ps and nearly sameremnant polarization. The saturate polarizations for the films with x = 0.00 to 0.20 are 80.7 C/cm2,91.1 C/cm2, 83.7 C/cm2, 64.9 C/cm2 and the remnant polarizations (Pr are 33.7 C/cm2, 36.8C/m2, 34.4 C/cm2 and 37.6 C/pm

30、2 at an applied field 726 kV/cm., respectively. The films with x 0.2 show small coercive filed and large saturation polarization. The Pr of the pure PZT is larger thanthat of Zhu and less than the (111 orie nted PZT films on Pt/Ti/SiO2/Si substrates 18, 19. From theresults above we can find that thr

31、ough the solid solution with BiFeO3, the saturate polarization issubsta ntially enhan ced since the Ps value for the film with x = 0.05 is 10 C/cm2 largercthan that of the pure PZT. There is no substantially change in the coercive filed since the films withx 0.2 have the n early same coercive fields

32、. While large coercive field is obviously for the film withx = 0.20. We suggest that the large coercive field is from the pin of domain wall by the spacecharges originate from the A and B sites substitution by Bi3+ and Fe3+. The ions radius of Fe 3+,Zr4+, Ti4+, Bi3+ and Pb2+ are 0.64 ?, 0.72 ?, 0.68

33、 ?, 1.03 ? and 1.32 ?, respectively. Because ofthe similar ion radius of Fe3+ to Zr4+ and Ti4+, Bi3+ to Pb2+, the in corporation of BiFeO3 will resultin A site occupati on for Bi3+ and B site occupati on for Fe3+ to form stabilize perovskite structure.Since the radius of Fe3+ is less than that of Zr

34、 4+ and Ti4+, we expect larger vibrating space for theFe3+ in the oxyge n octahedr on thus obta ins more intense polarizati on. On the other hand, thesusceptibility of Fe3+ is less tha n that of Ti4+ and Zr4+ and the excess substituti on of Ti4+ andZr4+ with Fe3+ will lead to the reduct ion therefor

35、e the film with x = 0.2 has the least Ps.Fig. 3 AFM photos of PZT1-x-BF0 x films for x = (a 0.00, (b 0.05, (c 0.10 (d 0.20.Figure 5 shows the dielectric con sta nt and dissipati on factor as a fun cti on offreque ncyrange.I（lLjlllollllLlL JollllLllllUlll lllilllilallilliilllllllaiaalllllttllFig. 5 D

36、ielectric properties of the (a dielectric con sta nt and (b dielectric loss of thePZT1-x-BFOx films with x= The dielectric loss is shown in Figure 3s with x = 0 and 0.10 havelow dielectric loss crystal grain of it.from 1100 Hz to 1.0 MHz at room temperature for the PZT1-x -BFO x films with x=0.00to

37、0.20. The films show enhan ced dielectric property for the dielectric con sta nts of the filmswith x=0.10 and 0.20 are larger than the pure PZT film below 400 kHz. The film with x=0.05has the least dielectric constant above 80 kHz. It is suggested that the dielectric constant isdetermined by the pol

38、arization in ferroelectrics. As has been discussed above, the incorporati on of BiFeO3 leads to the enhan ced ionic displace in octahedral therefore resultsin enhan ced polarizati on, which brings on the in crease of dielectric con sta nt. We can alsoobserve the drastic decrease of dielectric con st

39、a nt above 100 kHz for the film with x=0.2. Asdiscussed in our previous work 20, the falli ng in dielectric con sta nt arises from the factthat polarizati on does not occur in sta ntan eously with the application of the electric fieldbecause of inertia. At low frequencies, all the polarizati ons con

40、 tribute. As freque ncy is increased, those with large relaxati on times cease to resp ond and hence the decrease indielectric con sta nt.Fig. 4 electrichysteresis loops for PZT1-x-BFOx films.0.0 to 0.20.(b, the filmat low freque ncies and the dielectric loss beg in to in crease drastically n ear100

41、 kHz. For the film with x = 0.10, dielectric loss was observed to decrease with frequencybetween 110 kHz to 10 kHz and it is attribute the effects of DC conduction. The large DC conducti on is attributed to the space charges in troduced by aliovale nt substitution of Pb2+ andFe3+. Below 300 kH z, th

42、e film with x = 0.2 has the largest dielectric loss at the samefrequency and it may be related to the larger.c n Figure 6 shows J-E characteristics of the PZT1-x-BFOx filmswith x=0, 0.05, 0.10 and 0.20 at both polarities of the applied voltages. From which we findthat the pure PZT

43、 film has the lowest current densities at the same applied field. Obviously,the leakage curre nts den sity is in creased with the x monotono usly. Compari ng with thepure PZT film, the leakage curre nt den sity in creased by n early six orders of magnitude forthe film with x=0.2. It has been well es

44、tablished that the leakage current in ferroelectrics isdomin ated by space charges. Therefore abundant space charges were produced by the incorporatio n of BiFeO3. We suggest that the space charges are orig in ated from the following three reas ons: (1 cati on vaca ncies created by the substitution

45、of Fig. 6 J-Echaracteristics of PZT1-x-BFOx films with x=0 to 0.2. Ti4+ with Fe3+. (2 anion vaca nciescreated by the substituti on of Pb2+ with Bi3+. (3 oxyge n vaca ncies created by the vale neereduct ion of Fe3+ species to Fe2+. As discussed above the increasing is attributed to theincreasing of s

46、pace charges by the incorporation of BFO. 4 Con clusi ons BiFeO3 modifiedPZT films were prepared with sol-gel process. PZT1-x- BFOx films with x=0 to 0.2 weredeposited on LaNiO3/SiO2/Si substrates and fully crystalli ne films were obta ined at an anneali ng temperature of 600C. Through theincorporat

47、ion of BiFeO3, the ferroelectricity anddielectric property are substantially enhanced. Remnant polarizations of 33.7 C/cm2, 36.8C/cm2, 34.4 C/cm2 and 37.6 pC/cm2 are observed respectively for the films with x=0, 0.05,0.10 and 0.20. Enhanced ferroelectricity and dielectric property are thought to be

48、determined by the enhan ced polarizati on by the substituti on of Zr4+ and Ti4+ with Fe3+. Theleakage con duct ion is greatly in creased by the in corporati on of BiFeO3 and is thought todue to the can ti on and anion vaca ncies produced by the substituti on of A and B site withBi3+ and Fe3+. -6-.c n Refere nces 1 M. M. Kumar, A. Srini vas, G. S. Kumar, andS. V. Surya naraya na, J. Phys.: Con de ns. Matter 11,8131 (1999. 2 I. Sos no wska, T.P.Neumaier, and E. Steichel