Surface domain structures and mesoscopic phase transition in relaxor ferroelectrics
A.L. Kholkin,1 A. N. Morozovska,2 D. A. Kiselev,1 I.K. Bdikin,1 B.J. Rodriguez,3 P. Wu,4 A.A. Bokov,5 Z.-G. Ye,5 B. Dkhil,6 L.-Q. Chen,4 M. Kosec,7 S. V. Kalinin8
1University of Aveiro, Portugal, 2National Academy of Science of Ukraine, 3University College Dublin, Ireland 4Pennsylvania State University, 5Simon Fraser University, Canada, 6Ecole Centrale Paris, 7Jozef Stefan Institute, Slovenia, 8Oak Ridge National Laboratory
PFM depth profiling of mesoscopic domains
Mesoscopic polarization orderings and dynamics have been studied in several families of ferroelectric relaxors. The combination of imaging and spectroscopy data indicates the presence of two effective order parameters with dynamic and static components, respectively. The symmetry breaking in the surfaces results in the formation of non-fractal ordered structures with characteristic ~100 nm length scale. These domain structures are only weakly sensitive to electric field, and gradually disappear with increasing temperature. The dynamic polarization component is (within the experimental error) uniform within the material and can be easily manipulated by the field of a PFM tip. Both static and dynamic polarization components exist well above the temperature of maximum bulk dielectric constant, and their temperature behavior is strongly dependent on the crystallographic plane.
Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameter gives rise to emergence of unusual properties, including non-exponential relaxations, memory effects, polarization rotations, and a broad spectrum of bias- and temperature-induced phase transitions. Despite more than 40 years of extensive research, the most basic aspect of these materials – e.g. the existence and nature of order parameter – has not been understood thoroughly. The present study clearly illustrates the importance of mesoscopic polarization patterns that are until now overlooked by major theories of relaxor states. An obvious and open question is the relation of these observations to recent neutron-based studies illustrating the presence of static and dynamic order parameters in relaxors, as well as reports on local strains and domain-like dynamics and surface layers.
This work was published on the web in Advanced Functional Materials, April 12, 2011, doi: 10.1002/adfm.201002582. A portion of this research (S.V.K) was conducted at the Center for Nanophase Materials Sciences, which is sponsored at ORNL by the Office of Basic Energy Sciences,US Department of Energy (project CNMS2009-090). D.A.K. and A.L.K. are grateful to the Portuguese Foundation for Science and Technology (FCT) for the support within the PhD fellowship grant SFRH/BD/22391/2005 and the FCT project PTDC/FIS/81442/2006. A.A.B. and Z.-G.Y. are grateful to the U.S. Office of Naval Research (N00014-06-1-0166) and the Natural Science & Engineering Research Council of Canada (NSERC) for the support.