Enhanced polarization in strained BaTiO 3 from first principles
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Enhanced polarization in strained BaTiO3 from first principles J. B. Neaton, C.-L. Hsueh, and K. M. Rabe Department of Physics and Astronomy, Rutgers University Piscataway, NJ 08854-8019 ABSTRACT The structure, polarization, and zone-center phonons of bulk tetragonal BaTiO3 under compressive epitaxial stress are calculated using density functional theory within the local density approximation. The polarization, computed using the Berry-phase formalism, increases with increasing tetragonality and is found to be enhanced by nearly 70% for the largest compressive misfit strain considered (-2.28%). The results are expected to be useful for the analysis of coherent epitaxial BaTiO3 thin films and heterostructures grown on perovskite substrates having a smaller lattice constant, such as SrTiO3 . INTRODUCTION With recent advances in oxide epitaxy, coherent growth of nearly perfect ultrathin perovskite films and heterostructures is now possible [1, 2, 3]. In these systems, individual constituent layers are under mixed mechanical boundary conditions: constrained to the substrate lattice constant in-plane, the films are free to relax in the normal direction. The strains achieved in this way can be quite significant, and can be controlled to tune structure, ferroelectric, and dielectric properties of these nanostructured materials [4, 5]. For example, the polarization could be increased over that of known bulk compounds [6, 7], improving the performance of ferroelectric field-effect transistors and nonvolatile memories. When the interfaces in lattice-matched heterostructures are between sufficiently similar materials, even the thinnest layers can be well described by considering the behavior of the bulk under the same boundary conditions. Thus, for example, many properties of BaTiO3 /SrTiO3 superlattices can be understood by considering the effects of large strains on bulk BaTiO3 . This has led to great interest in information about highly strained bulk and film states in the perovskites, for example as presented previously in a phenomenological Landau-Devonshire framework [7, 8, 9]. Here we perform first-principles calculations and obtain information about the structure, spontaneous polarization, and zone-center phonons of bulk tetragonal BaTiO3 with misfit strains down to about -2.3%. While our results correspond to zero temperature, previous work [7] suggests that in this high-strain regime, the tetragonal phase is stable with increasing temperature and thus our analysis is relevant to the study of ultrathin BaTiO3 films and BaTiO3 /SrTiO3 superlattices at room temperature [10]. METHODOLOGY To predict the ground state structure of strained BaTiO3 and compute the associated polarization, we use density functional theory (DFT) [11] within the local density approxima-
D10.26.1 Downloaded from https:/www.cambridge.org/core. University of Arizona, on 14 Mar 2017 at 02:11:18, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-718-D10.26
tion (LDA) [12], as
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