Investigation on propagation process of electrically induced fatigue cracking using AFM

ARTICLES .Chinese Science Blletin 2005 Vol. 50 No.19 2145- 2148lationship between the domain switching and electricallyinduced fatigue cracking in BaTiO3 single crystal by inInvestigation on propagationsitu AFM observation. .process of electrically induced 1 Experimental procedureUnpoled and poled BaTiO3 single crystals with a sizefatigue cracking using AFMof 1X5X5 mm3 were used in this study. The poling di-rection was the [001] direction, and the indentation testWANG Fang, SU Yanjing, HE Jianying, QIAO Lijie .was carried out on the polished (100) surface with a load& CHU Wuyangof 0.98N and a dwell time of 20 s. A negative field of E =1.8E, where E.= 102 V/mm served as the coercive field,Beiing. Beiing 100083. ChinaCorrespondence should be addressed to Su Yanjing (email: yjsu@mater.was first applied in the [00 1]direction for one minute.ustb.edu.cn)After in situ examining the domain switching band aroundustb.crack tip using AFM, a same negative field was appliedAbstract Propagation process of electrically inducedsecondly for one minute. Then, a positive field of E=1.8E。fatigue cracking in BaTiO3 single crystal has been studiedwas applied. The electric field was alternated for sevenusing atomic force microscope (AFM). The results show thattimes including negative field of fours times and positivealternating electric field generates a random domain switch-field of three times.ing around indentation cracks instead of a cyclic domainswvitching and an arrest indentation crack can be re-initiated 2 Results and discussionby applying either positive or negative alternating electricThe domain switching bands in an unpoled BaTiO3field.Keywords: domain switching, atomic force microscope, elctricallyan optical microscope and AFM. The width of the domaininduced fatigue cracking.switching bands measured by AFM is about 8 um, whichDOI: 10.1360/982004 508is basically consistent with that by an optical microscope.For both unpoled and poled samples etched after in-A cyclic crack growth in ferroelectrics could be in- denting, the 9(duced by an alternating electric field"- l. Various models the interior flank of the indentation cracks, i.e. OAB andfor electrically induced fatigue cracking have been re- OCD zones, as shown in Fig. 2(a). Using height model ofviewed by Yango'. A model of small-scale discharge forAFM, the AFM image of the indentation crack is shown infatigue crack growth was proposed by Lynch et al.23. ZhuFig. 2(b). The domain switching zone PA in Fig. 2(b) isand Yang proposed a mechanics model for fatigue crack composed of domain switching bands shown in Fig. 2(c).growth driven by cyclic domain switching. Under an The height of the convex domain switching bands is aboutalternating electric field, the field concentrated at the 6 nm based on the section analysis of the bands, as showncrack tip causes the ferroelectrics to undergo cyclic do- in Fig. 2(d).main switching. Driven by the domain switching inducedUsing deflection model of AFM, the cracks of OA andstress field, the crack experiences a repeated process of OB are white and that of OC and OD are black (Fig. 3().initiation, growth, arrest, and re-initiation'.. However On the other hand, the domain switching bands in thethere is no direct evidence on whether field-induced cyclic OAB zone are black, but those in the OCD zone are whitedomain swithing results in crack growth.(Fig. 3(a)). After applying a negative field of 1.8Ec, theFor ferroelectric single crystals, domain switching can domain switching bands in the OAB and OCD zones in-be observed using a polarized optical microscope'9. Our crease, but there is no crack growth (Fig. 3(b). After the .experiments, however, showed that the domain switching negative field is applied secondly, there form new domainobserved using the polarized optical microscope was only switching bands of MN, which are far away from the do-a party of the whole domain switching zone, which could main switching zone induced by indenting, as shown inbe exhibited through etching using HCl+HF solution.Fig. 3(c). After applying a positive field of 1 8Ec, there areEtching itself, however, could enhance domain switching no evident changes in the bands and the cracks (Fig. 3(d)).and crack propagation, therefore, the relationship between The cracks and the bands no more change evidently after ahe electric field-induced domain switching and crack negative field is applied thirdly (Fig. 3(e)). After the posi-growth under alternating electric filed cannot be in situtive field is applied secondly, the bands of MN disappearinvestigated through etching.and the new bands of GH and OK form (Fig. 3(). AfterAtomic force microscope (AFM) can be used to find the negative field is applied fourthly, the new bands of GHthe convex on the surface; thus, it is possible that the 90° get widened (Fig. 3(g)). After the positive field is applieddomain switching zone or bands can be observed using thirdly, no evident change occurs (Fig. 3(h)). Although theAFM. The objective of this paper is to investigate the re-domain bands change, continnonslv, cracks do not propa-中国煤化工Chinese Science Blletin Vol. 50 No. 19 October 2005YHCNMH G2145.ARTICLES- 60.0- 40.0t 20.0S0 um20.0 40.0 60.0 80.0 umFig. 1. The domain switching band in an unpoled BaTiO3 single crystal etching using HF +HCI. (a) Optical photography; (b) AFM image.50um(dP(b0 uimFig. 2. The dormain swithing zones limited to interior flank of the indentation cracks in poled Ba TiO3 single crystal. (a) Optical pictureafter etching; (b) AFM image on the polished surface; (C)AFM image of crack AP and domain switching bands; (d) section analysis ofthe switching bands.ate under the alternating electric field.from T to X and the band TS widens (Fig. 4(c)). AfterFig.4(a) is another indentation crack. After applying a applying a positive field of 1 .8Ec, the crack tip propagatesnegative field of 1.8Ec, the domain switching bands grow, continuously, and the band TS widens further (Fig. 4()).e.g. from AB to AB' and from CD to CD', while the crack The crack tip propagates continuously under the alternat-tip propagates from G to T, and a new band TS forms at .ing electric field (Fig. 4()). After the positive field is ap-the crack tip, as shown in Fig. 4(b). After the negative is plied thirdly, a new crack PXY initiates in the domainapplied secondly, the domain switching zone get widened switching zone (Fig.4(f).from OB to OF, the crack tip propagates continuouslyFigs. 2 and 3 indicate that the domain switching zones中国煤化工2146Chinese Science 1MHC N M H Gctober 2005.ARTICLES(a)E-0(h) A--188YC)E-ISE(0)E--1.8E(e)E:--18E①E,--1.8E。Fig. 4. The domain switching, crack propagating and a new crack initiating under alternating electric field.(i) An alternating electric field generates a randomcyelic ectric loading, J. Mech. Plhys Solids, 199, 47: 81-97.domain switching instead of a cycle domain switching.5. Zhu, T, Fang, F, Yang, W,, Fatigue crack growth in frroelectric(ii) An arrest crack can be re-initiated not only by ap-ceramics below the coercive field, J. Mater. Sci. Lett, 1999, 18:plying a reverse field but also by a same directive field.1025- 1027.Acknowledgments This project was supported by the Key Project for6. Yang, W., Mechatronic Reliability, Berlin: Springer; 2002, 29, 225.Ministry of Education of the People's Republic of China (No. 104021).7. Yang, W, Fang, F, Tao, M., Critical role of domain switching onReferencesthe fracture toughness of poled frroelctrics, Int. J. Solids Structs,2001, 28: 2203- -211.growth in piezoelectrics, J. Am. Ceram. Soc, 1994, 77: 1783-8. Busche, M. J, Hsia, K. J, Fracture and domain switching by in-1786dentation in barium titanate single crystal, Scripta Mater, 2001, 44:2. Lynch, C. S., Yang, W., Collier, L., Suo, Z., Mcmeeking, R. M.,207-212.Eletric field induced cracking in frolelrie ceramics, Frrelec-9. Fang, F, Yang, W., Indentation-induced cracking and 90° domaintrics, 1995, 166: 11-30.switching pattern in barium titanate ferroelectric single crystals3. Lynch, C. s., Chen, L., Suo, Z., Mcmeeking, R. M., Yang, W. J,under dfferent poling, Mater Lett, 2002, 57: 198- -202.Crack growth in frrelelcrice ceramics driven by cyclic polarization10. 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