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Determining polarity in ferroelectric materials using precession electron diffraction and cepstral analysis
Brown, Colton Mis, Allison Holtz, Megan
Brown, Colton
Mis, Allison
Holtz, Megan
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2024-04
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Understanding local crystallography is necessary for understanding ferroelectric behavior in materials. Key properties to know include lattice parameters, interatomic spacings, and polarity. One tool to learn these properties is scanning transmission electron microscopy (STEM), which can measure a diffraction pattern (kx, ky) at every scan position (x, y). This allows crystallographic properties to be investigated at the nanometer scale. However, diffraction signals can contain artifacts from sample thickness and mistilt. These artifacts may be suppressed with precession electron diffraction (PED), which has the additional benefit of increasing the number of reflections in the diffraction pattern. In this work, we perform analytical calculations to assess the efficacy of using PED combined with cepstral analysis to measure polarity in lead magnesium niobate-lead titanate (PMN-PT). Taking the Fourier transform of the logarithmically scaled diffraction pattern yields the exit-wave power cepstrum (EWPC) which yields interatomic spacings in the crystal. To extract polarity, we use the imaginary component of the transform which contains the antisymmetric information, which is called the exit-wave imaginary cepstrum (EWIC). The EWIC transform is improved by having more higher-order diffraction disks, which is possible through PED. It was found that PED improves the EWIC signal: as precession angle was increased from 0° to 0.5° to 1°, signal noise decreased and dipole moments were better resolved in scenarios with and without mistilt. These results indicate that cepstral analysis of real samples may benefit from PED.
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