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.
Subscribe to Journal
Get full journal access for 1 year
only $17.42 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Scott, J. F. & Araujo, C. A. P. d. Ferroelectric memories. Science 246, 1400–1405 (1989).
Waser, R. (ed.) Nanoelectronics and Information Technology (Wiley-VCH, 2003).
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).
Streiffer, S. K. et al. Observation of nanoscale 180∘ stripe domains in ferroelectric PbTiO3 thin films. Phys. Rev. Lett. 89, 67601–67604 (2002).
Junquera, J. & Ghosez, P. Critical thickness for ferroelectricity in perovskite ultrathin films. Nature 422, 506–509 (2003).
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).
Fong, D. D. et al. Ferroelectricity in ultrathin perovskite films. Science 304, 1650–1653 (2004).
Lichtensteiger, C., Triscone, J.-M., Junquera, J. & Ghosez, P. Ferroelectricity and tetragonality in ultrathin PbTiO3 films. Phys. Rev. Lett. 94, 047603 (2005).
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).
Kim, Y. S. et al. Critical thickness of ultrathin ferroelectric BaTiO3 films. Appl. Phys. Lett. 86, 102907 (2005).
Cohen, R. E. Origin of ferroelectricity in perovskite oxides. Nature 358, 136–138 (1992).
Fong, D. D. et al. Stabilization of monodomain polarization in ultrathin PbTiO3 films. Phys. Rev. Lett. 96, 127601 (2006).
Kim, D. J. et al. Polarization relaxation induced by a depolarization field in ultrathin ferroelectric BaTiO3 capacitors. Phys. Rev. Lett. 95, 237602 (2005).
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).
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).
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).
Despont, L. et al. Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films. Phys. Rev. B 73, 094110 (2006).
Nagarajan, V. et al. Size effects in ultra-thin epitaxial ferroelectric heterostructures. Appl. Phys. Lett. 84, 5225–5227 (2004).
Nagarajan, V. et al. Scaling of structure and electrical properties in ultra-thin epitaxial ferroelectric heterostructures. J. Appl. Phys. 100, 051609 (2006).
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).
Williams, D. B. & Carter, C. B. Transmission Electron Microscopy (Plenum, New York, 1996).
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).
Jia, C. L., Lentzen, M. & Urban, K. Atomic-resolution imaging of oxygen in perovskite ceramics. Science 299, 870–873 (2003).
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).
O’Keefe, M. A. & Kilaas, R. Advances in high-resolution image simulation. Scan Microsc. Suppl. 2, 225–244 (1988).
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).
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).
Bellaiche, L. & Vanderbilt, D. Intrinsic piezoelectric response in perovskite alloys: PMN-PT versus PZT. Phys. Rev. Lett. 83, 1347–1350 (1999).
Kretschmer, R. & Binder, K. Surface effects on phase transitions in ferroelectrics and dipolar magnets. Phys. Rev. B 20, 1065–1076 (1979).
Sai, N., Kolpak, A. M. & Rappe, A. M. Ferroelectricity in ultrathin perovskite films. Phys. Rev. B 72, 020101 (2005).
Catalan, G. et al. Polar domains in lead titanate films under tensile strain. Phys. Rev. Lett. 96, 127602 (2006).
Munkholm, A. et al. Antiferrodistortive reconstruction of the PbTiO3(001) surface. Phys. Rev. Lett. 88, 016101 (2002).
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).
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).
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.
The authors declare no competing financial interests.
About this article
Cite this article
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
physica status solidi (b) (2020)
Advanced Materials Interfaces (2020)
The interplay of work function and polarization state at the Schottky barriers height for Cu/BaTiO3 interface
Applied Surface Science (2020)
Causal analysis of competing atomistic mechanisms in ferroelectric materials from high-resolution scanning transmission electron microscopy data
npj Computational Materials (2020)
Journal of Alloys and Compounds (2020)