Nonlinear optical method for crystallography analysis in lead zirconate titanate

The symmetry and structure of ferroelectric films determines most of its properties. Nonlinear optical technique of second harmonic generation (SHG) is widely accepted for remote and fast qualitative characterization of ferroelectric films. We develop a method for a quantitative characterization of the local symmetry and structure of ferroelectric films. The method is based on the SHG azimuthal dependences measurements following by fitting procedure by analytical equation and gives the ratio of phases as well as the fraction of differently oriented crystallographic faces. Unlike traditional techniques for crystallographic analysis nonlinear-optical technique is non-destructive, non-invasive, and does not require thin lamellae fabrication. SHG is sensitive to symmetry of crystal as well as to relative orientation of incident radiation polarization plane and crystallographic planes, so a technique based on SHG intensity measuring (SHG polarimetry) can be used as a diagnostic technique to determine crystal symmetry and orientation.

This technique is tried out on lead zirconate titanate thin films. Depending on the annealing time of pyrochlore phase two types of structure are obtained: continuous perovskite polycrystalline film consisting of truncated spherulites and isolated spherulites embedded into pyrochlore matrix. The same sample is studied by nonlinear optical technique and by electron diffraction method. These results are compared. It was shown by electron diffraction that PZT samples had (111) orientation in the center of spherulites and that this orientation uniformly rotates to the sides. This behavior was taken into account in analytical model.

The work is supported by the Ministry of Science and Education of RF (Project No.075-15-2022-1131)