Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films


Typically, polarization and strain in ferroelectric materials are coupled, leading to the generally accepted direct relation between polarization and unit-cell tetragonality. Here, by means of high-resolution transmission electron microscopy we map, on the unit-cell scale, the degree of tetragonality and the displacements of cations away from the centrosymmetry positions in an ultrathin epitaxial PbZr0.2Ti0.8O3 film on a SrRuO3 electrode layer deposited on a SrTiO3 substrate. The lattice is highly tetragonal at the centre of the film, whereas it shows reduced tetragonality close to the interfaces. Most strikingly, we find that the maximum off-centre displacements for the central area of the film do not scale with the tetragonality. This challenges the fundamental belief in a strong polarization–tetragonality coupling in PbTiO3-based ferroelectrics, at such thicknesses. Furthermore, a systematic reduction of the atomic displacements is measured at the interfaces, suggesting that interface-induced suppression of the ferroelectric polarization plays a critical role in the size effect of nanoscale ferroelectrics.

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Figure 1: Schematic view of the crystal structures.
Figure 2: HRTEM image of the PZT/SRO thin-film heterostructure.
Figure 3: Comparison of image contrast in experiment and calculation.
Figure 4: Quantitative comparison between experimental and calculated data.
Figure 5: Compilation of the measurements for PZT.
Figure 6: Spontaneous polarization.


  1. 1

    Scott, J. F. & Araujo, C. A. P. d. Ferroelectric memories. Science 246, 1400–1405 (1989).

    CAS  Article  Google Scholar 

  2. 2

    Waser, R. (ed.) Nanoelectronics and Information Technology (Wiley-VCH, 2003).

  3. 3

    Shaw, T. M., McKinstry, S.-T. & McIntyre, P. C. The properties of ferroelectric films at small dimensions. Annu. Rev. Mater. Sci. 30, 263–298 (2000).

    CAS  Article  Google Scholar 

  4. 4

    Streiffer, S. K. et al. Observation of nanoscale 180 stripe domains in ferroelectric PbTiO3 thin films. Phys. Rev. Lett. 89, 67601–67604 (2002).

    CAS  Article  Google Scholar 

  5. 5

    Junquera, J. & Ghosez, P. Critical thickness for ferroelectricity in perovskite ultrathin films. Nature 422, 506–509 (2003).

    CAS  Article  Google Scholar 

  6. 6

    Ahn, C. H., Rabe, K. M. & Triscone, J.-M. Ferroelectricity at the nanoscale: Local polarization in oxide thin films and heterostructures. Science 303, 488–491 (2004).

    CAS  Article  Google Scholar 

  7. 7

    Fong, D. D. et al. Ferroelectricity in ultrathin perovskite films. Science 304, 1650–1653 (2004).

    CAS  Article  Google Scholar 

  8. 8

    Lichtensteiger, C., Triscone, J.-M., Junquera, J. & Ghosez, P. Ferroelectricity and tetragonality in ultrathin PbTiO3 films. Phys. Rev. Lett. 94, 047603 (2005).

    Article  Google Scholar 

  9. 9

    Zembilgotov, A. G., Pertsev, N. A., Kohlstedt, H. & Waser, R. Ultrathin epitaxial ferroelectric films grown on compressive substrates: Competition between the surface and strain effects. J. Appl. Phys. 91, 2247–2254 (2002).

    CAS  Article  Google Scholar 

  10. 10

    Kim, Y. S. et al. Critical thickness of ultrathin ferroelectric BaTiO3 films. Appl. Phys. Lett. 86, 102907 (2005).

    Article  Google Scholar 

  11. 11

    Cohen, R. E. Origin of ferroelectricity in perovskite oxides. Nature 358, 136–138 (1992).

    CAS  Article  Google Scholar 

  12. 12

    Fong, D. D. et al. Stabilization of monodomain polarization in ultrathin PbTiO3 films. Phys. Rev. Lett. 96, 127601 (2006).

    CAS  Article  Google Scholar 

  13. 13

    Kim, D. J. et al. Polarization relaxation induced by a depolarization field in ultrathin ferroelectric BaTiO3 capacitors. Phys. Rev. Lett. 95, 237602 (2005).

    CAS  Article  Google Scholar 

  14. 14

    Gerra, G., Tagantsev, A. K., Setter, N. & Parlinski, K. Ionic polarizability of conductive metal oxides and critical thickness for ferroelectricity in BaTiO3 . Phys. Rev. Lett. 96, 107603 (2006).

    CAS  Article  Google Scholar 

  15. 15

    Sepliarsky, M., Stachiotti, M. G. & Migoni, R. L. Interface effects in ferroelectric PbTiO3 ultrathin films on a paraelectric substrate. Phys. Rev. Lett. 96, 137603 (2006).

    CAS  Article  Google Scholar 

  16. 16

    Duan, C. G., Sabirianov, R. F., Mei, W. N., Jaswal, S. S. & Tsymbal, E. Y. Interface effect on ferroelectricity at the nanoscale. Nano Lett. 6, 483–487 (2006).

    CAS  Article  Google Scholar 

  17. 17

    Despont, L. et al. Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films. Phys. Rev. B 73, 094110 (2006).

    Article  Google Scholar 

  18. 18

    Nagarajan, V. et al. Size effects in ultra-thin epitaxial ferroelectric heterostructures. Appl. Phys. Lett. 84, 5225–5227 (2004).

    CAS  Article  Google Scholar 

  19. 19

    Nagarajan, V. et al. Scaling of structure and electrical properties in ultra-thin epitaxial ferroelectric heterostructures. J. Appl. Phys. 100, 051609 (2006).

    Article  Google Scholar 

  20. 20

    Jiang, B., Peng, J. L., Bursill, L. A. & Zhong, W. L. Size effects on ferroelectricity of ultrafine particles of PbTiO3 . J. Appl. Phys. 87, 3462–3467 (2000).

    CAS  Article  Google Scholar 

  21. 21

    Williams, D. B. & Carter, C. B. Transmission Electron Microscopy (Plenum, New York, 1996).

    Google Scholar 

  22. 22

    Houben, L., Thust, A. & Urban, K. Atomic-precision determination of the reconstruction of a 90 tilt boundary in YBa2CU3O7−δ by aberration corrected HRTEM. Ultramicroscopy 106, 200–214 (2006).

    CAS  Article  Google Scholar 

  23. 23

    Jia, C. L., Lentzen, M. & Urban, K. Atomic-resolution imaging of oxygen in perovskite ceramics. Science 299, 870–873 (2003).

    CAS  Article  Google Scholar 

  24. 24

    Abrahams, S. C., Kurtz, S. K. & Jamieson, P. B. Atomic displacement relationship to curie temperature and spontaneous polarization in displacive ferroelectrics. Phys. Rev. 172, 551–553 (1968).

    CAS  Article  Google Scholar 

  25. 25

    O’Keefe, M. A. & Kilaas, R. Advances in high-resolution image simulation. Scan Microsc. Suppl. 2, 225–244 (1988).

    Google Scholar 

  26. 26

    Glazer, A. M. & Mabud, S. A. Powder profile refinement of lead zirconate titanate at several temperatures II. Pure PbTiO3 . Acta Crystall. B 34, 1065–1070 (1978).

    Article  Google Scholar 

  27. 27

    Fong, D. D. et al. Direct structural determination in ultrathin ferroelectric films by analysis of synchrotron x-ray scattering measurements. Phys. Rev. B 71, 144112 (2005).

    Article  Google Scholar 

  28. 28

    Bellaiche, L. & Vanderbilt, D. Intrinsic piezoelectric response in perovskite alloys: PMN-PT versus PZT. Phys. Rev. Lett. 83, 1347–1350 (1999).

    CAS  Article  Google Scholar 

  29. 29

    Kretschmer, R. & Binder, K. Surface effects on phase transitions in ferroelectrics and dipolar magnets. Phys. Rev. B 20, 1065–1076 (1979).

    CAS  Article  Google Scholar 

  30. 30

    Sai, N., Kolpak, A. M. & Rappe, A. M. Ferroelectricity in ultrathin perovskite films. Phys. Rev. B 72, 020101 (2005).

    Article  Google Scholar 

  31. 31

    Catalan, G. et al. Polar domains in lead titanate films under tensile strain. Phys. Rev. Lett. 96, 127602 (2006).

    CAS  Article  Google Scholar 

  32. 32

    Munkholm, A. et al. Antiferrodistortive reconstruction of the PbTiO3(001) surface. Phys. Rev. Lett. 88, 016101 (2002).

    CAS  Article  Google Scholar 

  33. 33

    van Helvoort, A. T. J., Dahl, O., Soleim, B. G., Holmestad, R. & Tybell, T. Imaging of out-of-plane interfacial strain in epitaxial PbTiO3/SrTiO3 thin films. Appl. Phys. Lett. 86, 092907 (2005).

    Article  Google Scholar 

  34. 34

    Vrejoiu, I. et al. Intrinsic Ferroelectric properties of strained tetragonal PbZr0.2Ti0.8O3 obtained on layer-by-layer grown, defect-free single-crystalline films. Adv. Mater. 18, 1657–1661 (2006).

    CAS  Article  Google Scholar 

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The authors thank A. Thust, J. Barthel and H. Kohlstedt for fruitful discussions. This work was partially supported by the National Science Foundation (NSF) under Grants DMR-0132918, NSF-MRSEC DMR-0080008 and an NSF US–Europe program DMR-0244288. V.N. also acknowledges the support of the Alexander von Humboldt Foundation for his stay in Germany and the financial support of an Australian Research Council Discovery Grant 0666231.

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Correspondence to Chun-Lin Jia.

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Jia, C., Nagarajan, V., He, J. et al. Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films. Nature Mater 6, 64–69 (2007). https://doi.org/10.1038/nmat1808

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