Direct observation of charge density and electronic polarization in fluorite ferroelectrics by 4D-STEM
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PUBLIC SUMMARY
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The real-space charge density of the ZrO2 with sub-Ångström resolution is observed.
The electronic contribution to the total spontaneous polarization is non-negligible.
The local polarization suggests a gradual increase in the covalent nature of the Zr-O bond.
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ABSTRACT
The fluorite ferroelectrics is extremely promising for memory applications due to the silicon compatibility and the robust ferroelectricity with decreasing size. However, the direct observation of local electronic polarization remains elusive, thereby hindering the comprehension of the atomic-scale origin of ferroelectricity. Here, we directly map the real-space charge density of the ZrO2 nanocrystal in its polar, nonpolar, as well as interphase regions with sub-Ångström resolution by four-dimensional scanning transmission electron microscopy (4D-STEM). Based on the variation of the electric dipole moments, we analyze the electronic contribution to the total spontaneous polarization, which reaches a maximum of 17.8%. In comparison to the continuous polarization in conventional ferroelectric units, the local polarization profile looks like a maple leaf edge at the tetragonal-orthorhombic phase interface, which suggests a gradual increase in the electronic polarization and the covalent nature of the Zr-O bond. We validate these findings with 4D-STEM simulations and calculations based on density functional theory. These findings provide atomic insights into the bonding nature and phase transition feature in fluorite oxides, and unravel the likely origin of ferroelectricity in ferroelectrics. -
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Wang S., Li X., Jia Y., et al., (2024). Direct observation of charge density and electronic polarization in fluorite ferroelectrics by 4D-STEM. The Innovation Materials 2(2): 100068. https://doi.org/10.59717/j.xinn-mater.2024.100068
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Wang S., Li X., Jia Y., et al., (2024). Direct observation of charge density and electronic polarization in fluorite ferroelectrics by 4D-STEM. The Innovation Materials 2(2): 100068. https://doi.org/10.59717/j.xinn-mater.2024.100068
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Figure 1.
Experimental setup and main principles
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Figure 2.
Real-space charge-density mapping and polar analysis in orthorhombic and tetragonal ZrO2
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Figure 4.
DFT calculation results of ZrO2 in the O-phase
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Figure 3.
Charge-density and polarization in polar-antipolar fixed state and the T-O phase interface
