研究目的
Investigating the presence and characteristics of monoclinic nanodomains in PMN-31%PT using scanning convergent beam electron diffraction (SCBED) to understand the high piezoelectric performance at the morphotropic phase boundary (MPB).
研究成果
The study successfully demonstrated the presence of monoclinic 60° ± α nanodomains in PMN-31%PT using SCBED, providing direct evidence of Cm-like symmetry at the nanoscale. This method enables the study of ferroelectric crystals of lower symmetry and challenges previous suggestions that observed monoclinic symmetry resulted from averaging between rhombohedral (R) or tetragonal (T) type nanodomains. The findings attribute local symmetry and polarization fluctuations to local chemical fluctuations resulting from random occupation of B-site cations.
研究不足
The technique's applicability is limited to thin samples due to the penetrating probe requirement. The study also acknowledges local fluctuations in symmetry and polarization, which could be attributed to local inhomogeneities, suggesting areas for further optimization and study.
1：Experimental Design and Method Selection:
The study utilized scanning convergent beam electron diffraction (SCBED) for symmetry mapping to identify local structure and polarization at the nanoscale.
2：Sample Selection and Data Sources:
A PMN-31%PT single crystal was selected, prepared by mechanical polishing and Ar ion-milling for electron transparency, followed by annealing to remove artificial domain structures.
3：List of Experimental Equipment and Materials:
A JEOL 2100 LaB6 transmission electron microscope (TEM) was used for the electron diffraction experiments.
4：Experimental Procedures and Operational Workflow:
SCBED was performed by positioning the focused electron probe on a rectangular grid across a selected area and recording the CBED patterns at each position. The recorded patterns were quantified using the normalized-cross correlation coefficient (c) and represented as a map.
5：Data Analysis Methods:
The symmetry of recorded patterns was quantified for the mirror element using the cross-correlation (CC) coefficient c by applying the mirror operation to the pairs of 1st and 2nd order reflections. Dynamic diffraction simulations using the Bloch wave method were carried out based on the approximation of an ionic model for atomic scattering of the crystal potential.
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