Ferroelectric and Multiferroic Layered Oxides. Mark A. Zurbuchen* and Darrell G. Schlom**. * Aerospace Corp., 2350 E. El Segundo Dr., El Segundo, CA 90405.
Characterization and Tomography of Nanoscale Domain Structures in Ferroelectric and Multiferroic Layered Oxides Mark A. Zurbuchen* and Darrell G. Schlom** * Aerospace Corp., 2350 E. El Segundo Dr., El Segundo, CA 90405 ** Materials Science and Engineering, Penn State University, 106 Materials Research Institute Bldg, University Park, PA 16803 The broad spectrum of electronic and optical properties exhibited by layered oxides with perovskiterelated structures offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired. As the epitaxial growth of an ever-increasing number of layered complex oxides is pursued, it has become clear that the interplay between these highly anisotropic phases and their more simply structured, often cubic, single-crystal substrates leads to specific types of domain and defect structures. Growth twin domains, out-of-phase domains, ferroelectric domains, and magnetic domains exist and interact within these materials in a complex manner.[1] Behavior of these materials is strongly influenced by these interactions, so it is imperative to understand their structure and interplay, ultimately in three dimensions. Three-dimensional reconstruction of domain structures, whether through discrete or traditional tomography methods, requires first that the domain structures be resolved. Several approaches are possible. Bright-field and high-resolution TEM imaging reveal translation boundaries such as outof-phase domain boundaries (OPBs) and stacking faults, due to decreased electron channeling in faulted regions. Geometric phase analysis reveals OPBs and their relative shifts, and other Fourier filtering techniques are used to image ferroelectric domains in zero-strain and other ferroelectrics. Dark-field imaging is used to image the domains of a strain-free ferroelectric material. Careful diffraction analysis and dark-field imaging reveal complicated growth twin domain structures. Shown below are examples of the resolved domain structures used for nanoscale tomographic reconstruction. The ultimate goal is a three-dimensional model usable to gain an understanding of the correlation and interplay of these structures in three dimensions. This necessitates the development of tomographic methods with nanoscale resolution. We will present the details and methods of studies of the domain structures of layered oxides, along with recent progress in extracting threedimensional structures of the domains. Correlations between defects and domains will be described. The impact of the domain structures and their interactions on the behavior of these materials will be discussed. References [1] M. A. Zurbuchen, W. Tian, X. Q. Pan, D. Fong, S. K. Streiffer, M. E. Hawley, J. Lettieri, Y. Jia, G. Asayama, S. J. Fulk, D. J. Comstock, S. Knapp, A. H. Carim, and D. G. Schlom, J. Mater. Res. (in press). [2] M. A. Zurbuchen, G. Asayama, D. G. Schlom, and S. K. Streiffer: Ferroelectric domain structure of SrBi2Nb2O9 epitaxial thin films. Phys. Rev. Lett. 88, 107601 (2002).
Fig. 1. A single frame used for tomographic reconstruction of the out-of-phase domain structure of the layered oxide Sr2RuO4, generated by geometric phase analysis.
Fig. 2. Single frames used for tomographic reconstruction of the OPB and ferroelectric domain structures in srBi2Nb2O9.[2] (a) HRTEM image, with OPBs indicated by arrows. (b) Ferroelectric domain map generated from (a), showing the 90° ferroelectric domain structure. Note that the OPBs correlate to non-ferroelectric or differently polarized regions in (b). Three-dimensional reconstruction resolves the interaction of these two networks of domains.
