Virtual piezoforce microscopy of polycrystalline ferroelectric films

An innovative methodology is presented that utilizes the experimental results of electron backscattered diffraction to map the crystallographic orientation of each grain, the finite element method to simulate the local grain-grain interactions, and finally piezoforce microscopy to infer the local properties of polycrystalline ferroelectric materials by comparing the output of the numerical calculation(s) with the experimental results. The proposed combined method resolves the local hysteretic and electromechanical interactions in polycrystalline ferroelectric films, thus quantifying the effects of grain corners and boundaries on the polycrystal's macroscopic response. For a polycrystalline lead zirconate titanate sample, a finite range of crystallographic orientations and epitaxial strains is found to enhance the out-of-plane electrical response of the film with respect to its single-crystal, stress-free counterpart. Results show that {111} oriented grains parallel to the normal of the surface of the film yield the largest polarization magnitude enhancement, compressive stresses, and built-in electric fields, as well as an asymmetry in the quasistatic coercive field. In the absence of epitaxial strains, {001} oriented grains will be enhanced in their out-of-plane hysteretic response through the in-plane compressive stresses provided by the local neighboring grains. For the studied sample, grain corners and boundaries become favorable sites for pinning or nucleation of ferroelectric domains, depending on the local state of stress and polarization. (c) 2006 American Institute of Physics.