Extrinsic scaling effects on the dielectric response of ferroelectric thin filmsJon F. Ihlefeld, Aaron M. Vodnick, Shefford P. Baker, William J. Borland, and Jon-Paul Maria Citation: Journal of Applied Physics 103, 074112 (2008); doi: 10.1063/1.2903211 View online: http://dx.doi.org/10.1063/1.2903211 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/103/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The effect of stress on the dielectric and tunable properties of barium stannate titanate thin films Appl. Phys. Lett. 94, 052902 (2009); 10.1063/1.3073743 Barium titanate nanocrystals and nanocrystal thin films: Synthesis, ferroelectricity, and dielectric properties J. Appl. Phys. 100, 034316 (2006); 10.1063/1.2218765 Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO 3 films J. Appl. Phys. 93, 2855 (2003); 10.1063/1.1540225 Diffuse phase transitions, electrical conduction, and low temperature dielectric properties of sol–gel derivedferroelectric barium titanate thin films J. Appl. Phys. 90, 1480 (2001); 10.1063/1.1367318 Pyroelectric Ba 0.8 Sr 0.2 TiO 3 thin films derived from a 0.05 M solution precursor by sol–gel processing Appl. Phys. Lett. 75, 3402 (1999); 10.1063/1.125307

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Extrinsic scaling effects on the dielectric response of ferroelectric thinfilms

Jon F. Ihlefeld,1,a� Aaron M. Vodnick,2 Shefford P. Baker,2 William J. Borland,3 andJon-Paul Maria1

1Department of Materials Science and Engineering, North Carolina State University, Raleigh, NorthCarolina 27695, USA2Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14850, USA3DuPont Electronic Technologies, Research Triangle Park, North Carolina 27709, USA

�Received 30 November 2007; accepted 28 January 2008; published online 8 April 2008�

Scaling effects in polycrystalline ferroelectric thin films were investigated by preparing bariumtitanate in a manner that maintained constant composition and film thickness while allowingsystematically increased grain size and crystalline coherence. The average grain dimensions rangedfrom 60 to 110 nm, and temperature dependence of permittivity analysis revealed diffuse phasetransitions in all cases. Maximum permittivity values ranged from 380 to 2040 for the smallest tolargest sizes, respectively. Dielectric hysteresis is evident at room temperature for all materials,indicating stability of the ferroelectric phase. Comparison of permittivity values at high electricfields indicates that the intrinsic dielectric response is identical and microstructural artifacts likelyhave a minimal influence on film properties across the sample series. Permittivity values, however,are substantially smaller than those reported for bulk material with similar grain dimensions. X-rayline broadening measurements were taken for the grain size series at the Cornell High EnergySynchrotron Source �CHESS�, which revealed coherent scattering dimensions substantially smallerthan the microscopy-determined grain size. Collectively these data sets suggest that permittivityvalues are influenced not only by grain size but also by the mosaic structure existing within eachgrain, and that thin film thermal budgets, which are several hundred degrees lower than used forbulk processing, are responsible for reduced crystalline coherence, and likely the origin of degradedelectromechanical response in thin film ferroelectrics. © 2008 American Institute of Physics.�DOI: 10.1063/1.2903211�

INTRODUCTION

During the last four decades there have been strong re-search efforts investigating the relationships linking crystal-line dimensions and ferroelectric properties in bulkceramics,1–6 particles,7,8 and thin films.9–20 Many of the is-sues in bulk ceramics have been resolved; for instance, inceramic BaTiO3, a domain wall density model can explainthe permittivity maxima at 0.7 �m,1 while series mixing ofhigh permittivity ferroelectric grains and low permittivitygrain boundaries can account for diminished permittivity asgrain size decreases to 40 nm.3 For thin films, however, thereremains a contentious debate concerning the origin of a rou-tinely observed scaling effect. In particular, the most trou-bling features are reductions in permittivity, remanent polar-ization, and phase transition temperatures. While severalmodels have been developed to describe the observed phe-nomena, including parasitic interfacial capacitancelayers,9,21,22 depolarization fields,13,23 electrode chargescreening,24,25 and strain gradients,26,27 all models fail to ex-plain why these diminished properties occur in size scalessubstantially greater than in bulk materials. For example,thin films show reduced permittivities and TC shifts at grainsizes and film thicknesses an order of magnitude greater than

bulk ceramic grain sizes.3,9,13,19,28,29 Further confoundingthese observations are recent demonstrations suggesting thata permittivity of 25 000, sharp phase transitions, and no ap-parent TC shift, can be achieved in freestanding barium titan-ate single crystals with thicknesses as low as 75 nm.14 Thisstudy suggests that diffuse phase transitions and decreasedpermittivities observed in materials with grain sizes greaterthan 75 nm cannot be explained with a grain size effectalone. Other studies on ultrathin leaded ferroelectrics haveshown that ferroelectricity can exist in films only several unitcell thick.10,11,18 These observations demonstrate that para-sitic nonferroelectric interface phases alone cannot explainscaling effects and reveal a substantial gap in understanding.

The differences between bulk ceramics, machined singlecrystals, and thin films are best understood in the context oftheir synthesis history. Bulk ceramics routinely are processedat temperatures in excess of 1100 °C to provide the masstransport necessary for sintering. Single crystal growth re-quires temperatures approaching or surpassing the meltingpoint and frequently assistance by a liquid flux. In contrast,thin films are generally limited in processing temperaturedue to film/substrate thermophysical properties, such as ther-mal expansion mismatch and film-substrate chemical reac-tion. These comparatively low temperatures impart limita-tions on the achievable crystallinity.30 Recently,compatibility of BaTiO3 with base metal substrates has beendemonstrated and has allowed access to previously unattain-

a�Electronic mail: jfi2@psu.edu. Present address: The Pennsylvania StateUniversity.

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able thermal budgets.31–35 This resulted in improved ferro-electric properties, including permittivities in excess of1500,31,33,34 which were attributed to enhanced grain size.Ultimately, however, these permittivities remain approxi-mately 40% lower than those observed in equivalent-grain-size bulk ceramics.3,28,29 In the present study, the connectionbetween grain size, crystallinity, and ferroelectric propertieswas investigated. A sample set was prepared where filmcomposition and thickness are constant, while grain size andcrystallinity are the control variables. We provide evidencethat mosaic structure inside ceramic grains provides a sub-stantial contribution to scaling effects in thin films and fur-ther the general understanding of scaling effects in ferroelec-tric materials.

EXPERIMENTAL PROCEDURE

BaTiO3 films were deposited via chemical solutiondeposition using a spin casting technique. A chemical precur-sor solution was prepared utilizing a chelate chemistry.36,37

Barium acetate �99.9% Aldrich Chemical� dissolved in gla-cial acetic acid and titanium isopropoxide �99.999% AldrichChemical� reacted with 2,4-pentanedione and diethanola-mine were combined in an equimolar ratio as determined byconstituent masses. The resulting solution had a 0.3M con-centration. The solution was spin cast onto 18 �m thick cop-per foils �Oak-Mitsui PLSP� at 3000 rpm for 30 s. The foilwas then placed on a hotplate at 250 °C for 7 min and 30 sto eliminate solvents and consolidate the gel. The coating/drying process was repeated five times, resulting in a filmwith an as-fired thickness of 650 nm. The coated substratewas cut into pieces, ensuring that each precursor sample hadthe same composition, thickness, and gel preparation treat-ments. These films were subsequently crystallized and sin-tered at temperatures ranging from 700 to 900 °C at 50 °Cintervals with a 30 min hold at the sintering temperature. Areductive atmosphere, controlled by the reaction of residualoxygen, hydrogen, and water vapor in a nitrogen carrier, wasutilized to prevent oxidation of the copper substrate. Totalfurnace pressure was maintained at 1 atm, while oxygen par-tial pressures ranged from 1�10−17 atm at 700 °C to 3�10−13 atm at 900 °C as monitored in situ by a solid oxideprobe �Australian Oxytrol Systems DS Series OxygenProbe�. These conditions are sufficient to prevent copper oxi-dation as predicted from thermodynamic reaction data.38

Samples were allowed to cool to 150 °C before removalfrom the crystallization furnace to prevent substrate oxida-tion. To minimize electrically active point defects associatedwith the low oxygen partial pressures, a subsequent anneal-ing at 550 °C and 10−8 atm O2 in a vacuum furnace wasemployed. Platinum top electrodes of �10−4 cm2 and 50 nmthick were deposited via radio frequency magnetron sputter-ing through a shadow mask. Capacitor dimensions were veri-fied with optical microscopy.

High-resolution x-ray diffraction experiments were con-ducted to determine coherent scattering lengths in the G2Hutch39 at the Cornell High Energy Synchrotron Source�CHESS� using symmetric diffraction geometry and a 1.43 Åwavelength. Instrumental broadening was characterized us-

ing a NIST 660a LaB6 powder line profile standard. Sampleswere rotated in plane during measurements and peaks werecaptured using an Ordela 1100x gas proportional positionsensitive detector at a resolution of 0.0075°/channel. Fouriertransform infrared �FTIR� spectra were collected to investi-gate the existence of hydroxyl and carbonate species in thedielectric using a Digilab FTS 6000 spectrometer equippedwith a liquid nitrogen cooled MCT �HgCdTe� narrow-banddetector. The spectra were collected at room temperaturewith a resolution of 2 cm−1 and were compiled as an averageof 64 scans to enhance the signal-to-noise ratio. A CP Re-search Thermomicroscopes atomic force microscope �AFM�in contact mode was used to characterize film surface topog-raphy over 9 �m2 regions. A JEOL 6400F Field-emissionscanning electron microscope �FE-SEM� operating at an ac-celerating voltage of 5 kV was used to image secondary andbackscattered electron signals of the film cross sections formorphology characterization and thickness measurements.Temperature and field dependent capacitance and loss tan-gent data were collected with a HP 4192A impedance ana-lyzer and a modified MMR Inc. cryogenic temperature stage.Samples were mounted in ceramic chip carriers with goldwire bonds connected to the top electrode and copper sub-strate for temperature response measurements. Samples werecooled to 100 K and heated at a rate of 5 K /min to 500 Kwhile recording the capacitance and dielectric loss. Electricfield dependencies of the permittivity and loss were collectedat room temperature at dc fields ranging from−250 to 250 kV /cm. All dielectric measurements were con-ducted with oscillator values of 0.8 kV /cm and 10 kHz.

RESULTS AND DISCUSSION

Figure 1 shows representative 3�3 �m2 AFM topo-graphical scans and cross-sectional FE-SEM images of the700, 800, and 900 °C processed samples. Each firing condi-tion produced samples with an equiaxed grain morphologyand low porosity levels. The cross-sectional images verifythat the equiaxed grain morphology is consistent through theentire thickness. The average thickness is the same for allsamples, which allows us to confidently associate all dielec-tric property variations to grain and crystallite size effectsand not thickness scaling or density variations. Average grainsize was calculated from the topographical AFM scans usinga Heyn linear intercept method.40 The results are shown inFig. 2 with the error bars representing 95% confidence inter-vals. Grain size scales with annealing temperature with 700and 900 °C anneals resulting in 66 and 114 nm averagegrain diameters, respectively.

The temperature and dc field dependence of permittivityis shown for the BaTiO3 processing temperature series inFig. 3. Both scale dramatically with grain diameter with thelarger-grained materials having larger peak permittivity val-ues and substantially sharper dependencies. The dielectricproperties for the finest-grained samples are consistent withother literature reports for films processed with similar ther-mal budgets regardless of deposition technique.9,12,13,36,41

The enhanced dielectric response observed for BaTiO3 withlarger grains is consistent with previously reported results for

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films deposited on base-metal electrodes31,33 and refractorymetal substrates.20 The phase transitions are diffuse in natureas is typical for fine-grained ferroelectrics. For the highest-temperature-processed material, there is a plateau in the di-electric constant over a broad temperature range. This maybe the result of a shift of the orthorhombic/tetragonal phasetransition to higher temperatures, as has been noted in otherfine-grained barium titanate ceramic studies.1,4 The field de-pendence verifies that increasing the processing temperaturedramatically increases the maximum permittivity as well asthe dielectric tunability. Dielectric hysteresis is observed foreach film, demonstrating that at room temperature grain sizesas fine as 66 nm show ferroelectric behavior. This is compa-rable to fine-grained bulk barium titanate, where hystereticpolarization–lectric field loops are reported at room tempera-ture for grain sizes as fine as 40 nm.3 In material of such finegrain size, however, it was shown that the remanent polar-ization and the slope of the hysteresis loops were diminishedwith decreasing grain dimensions, consistent with the resultsfrom the field-permittivity curves shown in Fig. 3. It is note-worthy to mention that the high-field permittivity is constantfor all samples, suggesting that the intrinsic permittivity isindependent of grain size, and that the permittivity increasewith processing temperature corresponds to extrinsic contri-butions.

The Curie points TC have been quantified and plotted inFig. 4. With the exception of the 700 °C sample, there isminimal or no phase transition temperature shift. For filmsprocessed between 750 and 900 °C, the Curie points are ap-proximately 120 °C, a value consistent with bulk ceramicsand single crystals.42,43 These TC values agree with well-prepared fine-grained bulk ceramic and glass-ceramic

FIG. 1. 3�3 �m2 AFM topographicalscans taken in contact mode ofsamples fired at �a� 700 °C, �b�800 °C, and �c� 900 °C and SEM sec-ondary electron images of the samesamples fired at �d� 700 °C, �e�800 °C, and �f� 900 °C.

FIG. 2. Calculated average grain size vs sintering temperature. Error barsindicate the 95% confidence interval �Ref. 40�.

FIG. 3. �Color online� �a� Temperature dependence of permittivity and losstangent and �b� field dependence of permittivity and loss tangent for eachprocessing condition. All measurements were conducted at 10 kHz with a0.77 kV /cm oscillator.

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samples, where a noticeable shift does not occur in materialscontaining grains/crystallites as small as 70 and 51 nmrespectively.3,5 A 60 °C shift is observed in the 66 nm grainsize film. A shift of this magnitude is not expected until acrystal size is less than 30 nm in bulk BaTiO3,5,7,44 a sizemuch finer than observed in this work. Observing a transitiontemperature shift in this grain size suggests that a secondaryeffect is present and quenching the dielectric response.

The relatively low processing temperature used to growthe finest-grained material could allow hydroxyl �OH−� andcarbonate �CO3

−� impurities to remain in the lattice, as hasbeen shown previously by other groups working on chemicalsolution and hydrothermally derived barium titanate.45–48

Hydroxyl groups incorporated into the barium titanate latticehave been demonstrated to stabilize the cubic phase and thuslower the ferroelectric/paraelectric phase transitiontemperature.46,47 FTIR spectra were taken for each sample todetermine if such impurities were present; the absorptionspectra are shown in Fig. 5. The spectral features below1500 cm−1 are associated with instrumental noise, the peakat 2350 cm−1 is produced by atmospheric carbon dioxide,while the broad peak ranging between 3000 and 3500 cm−1

results from the stretching mode of surface hydroxylgroups.48 Lattice hydroxyl stretching modes would appear asnarrow peaks at 3460 and 3510 cm−1 and are not present inany of the BaTiO3 films.49 It is possible that CO3

− impurtiesare present, however, and may be responsible for the anoma-lous loss tangent features in the 700 °C processed sample.50

Consequently, we conclude that processing-related impuritiesare minimally responsible for the trends in permittivity, tun-ability, or TC shift.

It is possible that a crystalline substructure exists withinthe BaTiO3 grains, and that the characteristic dimensions ofthis structure offer a more accurate descriptor of characteris-tic size to which trends in the dielectric response should berelated. To examine whether there were limits on coherentcrystal size at a length scale smaller that the grain size, thewidths of the diffraction peaks obtained in the synchrotronx-ray experiments were analyzed in detail. The well-knownWilliamson–Hall method51 can be used to separate the ef-fects of inhomogeneous strain and coherent scattering lengthon peak width. However, in the present experiments, the te-tragonal distortion of the BaTiO3 structure was not unam-biguously resolved, thus limiting the peaks available for theWilliamson–Hall analysis to the nondegenerate 111 and 222reflections. As a result, it was not possible to get accurateestimates of either scattering length or inhomogeneous strainusing this method. However, the data strongly suggest thatthe inhomogeneous strain contribution to peak broadening issimilar in all samples. Furthermore, both the lack of TC

shifts52,53 and observable substrate curvatures suggest thatabsolute strain levels �which could contribute to inhomoge-neous strains via strain redistributions throughout these elas-tically anisotropic samples� are low. Thus, it is reasonable toassume that changes in peak width can be attributed tochanges in the coherent scattering length alone. Conse-quently, the Scherrer method54 was employed using the 111reflections to obtain an estimate of coherent scattering di-mensions. The low diffraction angle of this peak minimizesstrain effects and its nondegeneracy eliminates broadeningdue to crystal structure asymmetry. Figure 6 shows the re-sults of this analysis plotted against processing temperature.Error bars represent the instrument resolution uncertainty. Incomparison to microstructure characterization, the synchro-tron scattering analysis indicates a steeper relationship be-tween coherent scattering length and processing temperatureand suggests a consistently smaller characteristic crystallinedimension. With these data in mind, it is suitable to considerthese, and perhaps many other similar materials, as an as-sembly of polycrystalline grains separated by defective grainboundaries, but with each grain containing several regions of

FIG. 4. Curie point TC as a function of measured grain size.

FIG. 5. FTIR spectra for each firing condition, focusing on the stretchingband of the hydroxyl group in chemical solution derived BaTiO3 thin films.

FIG. 6. �Color online� Average grain and coherent crystal sizes determinedusing AFM and x-ray line broadening measurements for each processingcondition.

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high-crystalline perfection, each slightly misoriented from itsneighbor, or separated by sufficient defect networks, as tointerfere with the x-ray coherent scattering process.

If the trends in dielectric properties are parametrized us-ing coherent scattering length as opposed to grain size, thecomparisons to bulk materials become substantially more fa-vorable. For example, the lowest temperature processed ma-terial in this work exhibited a TC shift of 70 °C. This transi-tion temperature shift occurs in bulk samples when grain sizefalls between 30 and 40 nm,5,7 a dimension very similar tothe 28 nm scattering length observed in the present x-rayanalysis. AFM measurements yield a grain size of 66 nm forthis sample, which does not produce a TC shift in bulk ma-terials. Subgrain defect boundaries may also describe the re-duced tunability and extrinsic contributions to permittivity.As fine-grained barium titanate is established to be singledomain, ferroelectric switching and domain wall motion oc-cur only at fields approaching the coercive value. Increasedintragranular mosaicity will likely reduce domain wall mo-bility and can account for the dielectric tunability and per-mittivity quenching.

A common metric for comparing size dependent ferro-electric properties is the room temperature permittivity. Fig-ure 7 shows data from several representative bulk ceramicand thin film studies of samples with similar grain dimen-sions and includes the present work plotted both as grain sizeand crystal coherence length.1,3,13,19 The permittivity valuesfor the two finest-grained samples in the present study com-pare favorably with permittivities of other thin films havingsimilar grain sizes. This is significant because their process-ing temperatures are comparable to those typically used andshows that similar results can be obtained regardless of depo-sition technique or substrate material. Increasing processingtemperature, however, results in dramatic increases in per-mittivity for a given characteristic dimension. In this com-parison, we see that using coherent scattering length insteadof grain size provides better agreement between bulk andthin film data; however, the values still fall short of bulkceramic reference data. The discrepancy between film and

bulk ceramic may be understood by considering the brick-wall model proposed by Payne and Cross55 and demonstratedby Frey et al.3 In this model, the reduction in permittivitywith grain size was an extrinsic dilution effect attributable tothe finite volume fraction of grain boundaries in a ceramicmonolith and the low permittivity of that defective material.Reduced grain size resulted in larger effective fraction of thatvolume and a lower composite permittivity. This model as-sumes a constant grain boundary thickness. In the presentcase, the lower thermal budgets used during synthesis arelikely to produce a generally more defective polycrystallinematerial that has a thicker grain boundary in addition to finiteporosity levels. Consequently, the dilution effect is stronger,and permittivity values for a similar grain size would belower. The onset of a TC shift, however, occurs at a similardimension for the current data set and those of Frey et al. andMcCauley et al. This is an important observation as a TC

shift is independent of grain boundary thickness. This agree-ment suggests that coherent scattering length is a viablemethod for parametrizing the properties of lower-temperature-processed ferroelectric materials, and that truesize effects occur when crystal sizes fall below the 30 nmrange.

CONCLUSIONS

This work describes the deposition of polycrystallinebarium titanate thin films on copper foils in an embodimentthat allows for uniform thickness and composition for arange of grain sizes from 66 to 114 nm. Investigation of thedielectric properties revealed a strong processing temperaturedependence on the permittivity and a phase transition tem-perature shift for the finest-grained material. The shift occursat a grain size much greater than would be expected frombulk ceramics. Synchrotron x-ray diffraction line broadeningmeasurements were used to show that the coherent crystallitesize is greatly reduced with the effect becoming more pro-nounced as the processing temperature is reduced. This di-minished crystallinity is responsible for the observed trendsand correlates well with bulk data. For processing tempera-tures typical to thin films, the crystal coherence length is ofthe order where size effects can begin to become appreciable.It is a reduction in crystal quality due to limited thermalbudgets that are responsible for the observed minimizedelectromechanical responses in thin film ferroelectrics. Roomtemperature dielectric properties consistent with well-prepared bulk ceramics are possible in thin layers if the crys-tallite size is controlled.

ACKNOWLEDGMENTS

The authors would like to acknowledge the financialsupport of E.I. du Pont de NeMours and Company, ResearchTriangle Park, North Carolina, USA. This work is based onresearch conducted at the Cornell High Energy SynchrotronSource �CHESS�, which is supported by the National Sci-ence Foundation under Award No. DMR-0225180.

1G. Arlt, D. Hennings, and G. de With, J. Appl. Phys. 58, 1619 �1985�.2W. W. Cao and C. A. Randall, J. Phys. Chem. Solids 57, 1499 �1996�.3M. H. Frey, Z. Xu, P. Han, and D. A. Payne, Ferroelectrics 206, 337

FIG. 7. �Color online� Measured values of permittivity at 25 °C as a func-tion of average grain or crystal size for each of the BaTiO3 thin filmsprepared in this study, the thin film works of Waser �Ref. 19� and Parker�Ref. 13�, and the bulk ceramics prepared by Arlt et al. �Ref. 1� and Frey etal. �Ref. 3�.

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�1998�.4K. Kinoshita and A. Yamaji, J. Appl. Phys. 47, 371 �1976�.5D. McCauley, R. E. Newnham, and C. A. Randall, J. Am. Ceram. Soc. 81,979 �1998�.

6Z. Zhao, V. Buscaglia, M. Viviani, M. T. Buscaglia, L. Mitoseriu, A.Testino, M. Nygren, M. Johnsson, and P. Nanni, Phys. Rev. B 70, 024107�2004�.

7M. Tanaka and Y. Makino, Ferroelectr., Lett. Sect. 24, 13 �1998�.8S. Wada, H. Yasuno, T. Hoshina, S. M. Nam, H. Kakemoto, and T. Tsu-rumi, Jpn. J. Appl. Phys., Part 1 42, 6188 �2003�.

9C. Basceri, S. K. Streiffer, A. I. Kingon, and R. Waser, J. Appl. Phys. 82,2497 �1997�.

10D. D. Fong, A. M. Kolpak, J. A. Eastman, S. K. Streiffer, P. H. Fuoss, G.B. Stephenson, C. Thompson, D. M. Kim, K. J. Choi, C. B. Eom, I.Grinberg, and A. M. Rappe, Phys. Rev. Lett. 96, 127601 �2006�.

11D. D. Fong, G. B. Stephenson, S. K. Streiffer, J. A. Eastman, O. Auciello,P. H. Fuoss, and C. Thompson, Science 304, 1650 �2004�.

12A. Lookman, R. M. Bowman, J. M. Gregg, J. Kut, S. Rios, M. Dawber, A.Ruediger, and J. F. Scott, J. Appl. Phys. 96, 555 �2004�.

13C. B. Parker, J. P. Maria, and A. I. Kingon, Appl. Phys. Lett. 81, 340�2002�.

14M. M. Saad, P. Baxter, R. M. Bowman, J. M. Gregg, F. D. Morrison, andJ. F. Scott, J. Phys.: Condens. Matter 16, L451 �2004�.

15S. Schmidt, J. W. Lu, S. P. Keane, L. D. Bregante, D. O. Klenov, and S.Stemmer, J. Am. Ceram. Soc. 88, 789 �2005�.

16S. K. Streiffer, C. Basceri, C. B. Parker, S. E. Lash, and A. I. Kingon, J.Appl. Phys. 86, 4565 �1999�.

17B. A. Strukov, S. T. Davitadze, S. G. Shulman, B. V. Goltzman, and V. V.Lemanov, Ferroelectrics 301, 157 �2004�.

18T. Tybell, C. H. Ahn, and J. M. Triscone, Appl. Phys. Lett. 75, 856 �1999�.19R. Waser, Integr. Ferroelectr. 15, 39 �1997�.20J. J. Xu, A. S. Shaikh, and R. W. Vest, IEEE Trans. Ultrason. Ferroelectr.

Freq. Control 36, 307 �1989�.21P. K. Larsen, G. J. M. Dormans, D. J. Taylor, and P. J. Vanveldhoven, J.

Appl. Phys. 76, 2405 �1994�.22L. J. Sinnamon, R. M. Bowman, and J. M. Gregg, Appl. Phys. Lett. 78,

1724 �2001�.23K. Binder, Ferroelectrics 73, 43 �1987�.24H. Y. Ku and F. G. Ullman, J. Appl. Phys. 35, 265 �1964�.25C. T. Black and J. J. Welser, IEEE Trans. Electron Devices 46, 776 �1999�.26T. M. Shaw, Z. Suo, M. Huang, E. Liniger, R. B. Laibowitz, and J. D.

Baniecki, Appl. Phys. Lett. 75, 2129 �1999�.27T. R. Taylor, P. J. Hansen, B. Acikel, N. Pervez, R. A. York, S. K. Stre-

iffer, and J. S. Speck, Appl. Phys. Lett. 80, 1978 �2002�.28M. T. Buscaglia, M. Viviani, V. Buscaglia, L. Mitoseriu, A. Testino, P.

Nanni, Z. Zhao, M. Nygren, C. Harnagea, D. Piazza, and C. Galassi, Phys.

Rev. B 73, 064114 �2006�.29A. V. Polotai, A. V. Ragulya, and C. A. Randall, Ferroelectrics 288, 93

�2003�.30R. E. Newnham, K. R. Udayakumar, and S. Trolier-McKinstry, in Chemi-

cal Processing of Advanced Materials, edited by L. L. Hench and J. K.West �Wiley, New York, 1992�, pp. 379–393.

31J. T. Dawley and P. G. Clem, Appl. Phys. Lett. 81, 3028 �2002�.32J. T. Dawley, R. J. Ong, and P. G. Clem, J. Mater. Res. 17, 1678 �2002�.33J. Ihlefeld, B. Laughlin, A. Hunt-Lowery, W. Borland, A. Kingon, and

J.-P. Maria, J. Electroceram. 14, 95 �2005�.34J. F. Ihlefeld, W. Borland, and J.-P. Maria, J. Mater. Res. 20, 2838 �2005�.35B. Laughlin, J. Ihlefeld, and J. P. Maria, J. Am. Ceram. Soc. 88, 2652–

2654 �2005�.36S. Hoffmann and R. Waser, J. Eur. Ceram. Soc. 19, 1339–1343 �1999�.37R. W. Schwartz, P. G. Clem, J. A. Voigt, E. R. Byhoff, M. Van Stry, T. J.

Headley, and N. A. Missert, J. Am. Ceram. Soc. 82, 2359 �1999�.38I. Barin, Thermochemical Data of Pure Substances, 3rd ed. �VCH, Wein-

heim, 1995�.39D. E. Nowak, D. R. Blasini, A. M. Vodnick, B. Blank, M. W. Tate, A.

Deyhim, D. M. Smilgies, H. Abruna, S. M. Gruner, and S. P. Baker, Rev.Sci. Instrum. 77, 113301 �2006�.

40ASTM E 112-96, Standard Test Methods for Determining Average GrainSize, Vol. 03.01 �ASTM International, 2003�.

41R. Thomas, V. K. Varadan, S. Komarneni, and D. C. Dube, J. Appl. Phys.90, 1480 �2001�.

42W. J. Merz, Phys. Rev. 76, 1221 �1949�.43A. von Hippel, R. G. Breckenridge, F. G. Chesley, and L. Tisza, Ind. Eng.

Chem. Res. 38, 1097 �1946�.44M. H. Frey, thesis, University of Illinois, 1996.45M. H. Frey and D. A. Payne, Phys. Rev. B 54, 3158 �1996�.46D. Hennings and S. Schreinemacher, J. Eur. Ceram. Soc. 9, 41 �1992�.47S. Wada, T. Suzuki, and T. Noma, J. Ceram. Soc. Jpn. 104, 383 �1996�.48S. Wada, T. Suzuki, and T. Noma, J. Ceram. Soc. Jpn. 103, 1220 �1995�.49S. Kapphan and G. Weber, Ferroelectrics 37, 673 �1981�.50The authors have performed unpublished in situ mass spectroscopy analy-

sis which reveals that 700 °C processed samples retain very small quan-tities of residual carbon-containing species.

51G. K. Williamson and W. H. Hall, Acta Metall. 1, 22 �1953�.52P. W. Forsbergh, Phys. Rev. 93, 686 �1954�.53N. A. Pertsev, A. G. Zembilgotov, and A. K. Tagantsev, Phys. Rev. Lett.

80, 1988 �1998�.54P. Scherrer, Nachr. Ges. Wiss. Goettingen, Math.-Phys. Kl. 2, 96 �1918�.55D. A. Payne and L. E. Cross, in Microstructure and Properties of Ceramic

Materials, edited by T. S. Yen and J. A. Pask �Science, Beijing, 1984�, pp.380–390.

074112-6 Ihlefeld et al. J. Appl. Phys. 103, 074112 �2008�

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