Strain-driven phase transitions and associated dielectric/piezoelectric anomalies in BiFeO3 thin films
ABSTRACT Strain-driven phase transitions and related intrinsic polarization, dielectric, and piezoelectric properties for single-domain films were studied for BiFeO 3 using phenomenological Landau–Devonshire theory. A stable and mixed structure between tetragonal and rhombohedral-like (monoclinic) phases is predicted at a compressive misfit strain of um=-0.0382 without an energy barrier. For a tensile misfit strain of um=0.0272 , another phase transition between the monoclinic and orthorhombic phases was predicted with sharply high dielectric and piezoelectric responses.
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ABSTRACT: Dielectric response of the BiFeO3 films in a parallel-plate capacitor configuration is studied in the frequency range 1 MHz–30 GHz and under dc electric field up to 45 V/μm in view of their application in tunable film bulk acoustic wave resonators. The observed relatively high permittivity 130 without remarkable frequency dispersion is explained by contribution of the domain wall vibrations. It is shown that the substrate induced strain and Maxwell-Wagner contributions are negligible. The measured dielectric response allows estimation of the BiFeO3 sound velocity and acoustic impedance as 3100 m/s and 26 · 10 kg/ms, respectively.Integrated Ferroelectrics 01/2012; 134(1):111-117. · 0.38 Impact Factor
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ABSTRACT: A phenomenological thermodynamic Landau–Devonshire theory is developed to investigate phase diagrams of epitaxial ferroelectric films with out-of-plane misfit strain induced by vertical nanocomposites. The thermodynamic potential of ferroelectric films is obtained based on the boundary conditions of three-dimensional clamping induced by the vertical nanocomposites. Our calculated results indicate that the out-of-plane misfit strain modulates the transition temperature and spontaneous polarization of ferroelectric films in a wide range even the substrate does not provide an effective in-plane misfit strain control. An enhanced critical transition temperature up to 803 °C in BaTiO3 films under a tensile out-of-plane misfit strain is predicted, which is consistent with the experimental result very well. The polarization properties of BaTiO3 films can also be effectively modulated by the out-of-plane misfit strain which is controlled by the volume fraction of nanopillars in the vertical nanocomposites. Our method provides a theoretical guide for the out-of-plane strain engineering of ferroelectric films.Applied Physics A 01/2013; · 1.69 Impact Factor