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Abstract
The influence of crystal orientations on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO3 thin films has been investigated using an expanded nonlinear thermodynamic theory. The calculations reveal that crystal orientation has significant influence on the phase stability and phase transitions in the misfit strain-temperature phase diagrams. In particular, the (110) orientation leads to a lower symmetry and more complicated phase transition than the (111) orientation in BaTiO3 films. The increase of compressive strain will dramatically enhance the Curie temperature TC of (110)-oriented BaTiO3 films, which matches well with previous experimental data. The polarization components experience a great change across the boundaries of different phases at room temperature in both (110)- and (111)-oriented films, which leads to the huge dielectric and piezoelectric responses. A good agreement is found between the present thermodynamics calculation and previous first-principles calculations. Our work provides an insight into how to use crystal orientation, epitaxial strain and temperature to tune the structure and properties of ferroelectrics.
Highlights
The polarization components experience a great change across the boundaries of different phases at room temperature in both (110)- and (111)-oriented films, which leads to the huge dielectric and piezoelectric responses
We have investigated the influence of crystal orientations on the phase diagrams, dielectric and piezoelectric properties of epitaxial BTO thin films with general substrate-induced misfit strains using an extended thermodynamic model
The misfit strain-temperature phase diagrams are calculated for (001), (110), and (111)-oriented BTO thin films by minimizing the free energies derived from the Landau Devonshire theory, in which different crystal orientations are considered through the transformation of thermodynamic variables from the local to global coordinate systems
Summary
To comprehend how the crystal orientations of ferroelectric films affect their physical properties, the insights and understandings from theoretical calculations are necessary besides experimental data. The typical theoretical models include the Landau-type phenomenological theory, phase field simulation and first-principles calculation.[31,32,33,34,35] most of the previous theoretical studies have focused on (001)-oriented thin films. The single-domain thermodynamic calculations of (001)-, (101)-, and (111)-oriented BFO films have predicted that the spontaneous polarizations depend on the film orientations and the types of substrate-induced strains.[36]. A comprehensive theoretical model is necessary to systematically study the orientation-dependent physical properties of ferroelectric thin films. Our results are compared to previous experimental and theoretical studies
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