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内容記述 |
Lead-based ferroelectrics such as Pb(Zr,Ti)O₃ (PZT) exhibit excellent dielectric properties. However, due to environmental concerns, development of high-performance lead-free alternatives is increasingly desired, despite their typically lower dielectric response. The superior performance of PZT arises from polarization rotation near the morphotropic phase boundary (MPB). A mechanism that has been emulated using structure gradient regions (SGRs) induced by lattice mismatch in artificial superlattices. In BaTiO₃/SrTiO₃ film systems, such SGRs have been shown to enhance dielectric properties. In this study, we extend this concept to ceramic particles by fabricating BaTiO₃–KNbO₃ (BT–KN) core–shell nanoparticles and investigating the effect of core size on SGR formation [1, 2]. Using 80 nm BaTiO₃ (BT80) cores, epitaxial KNbO₃ shells were grown via solvothermal synthesis. BT nanoparticles are known to exhibit size-dependent dielectric enhancement, and according to Hoshina’s model, internal structural gradients significantly affect their dielectric response [3]. To visualize the BT80–KN structure, Bragg coherent diffraction imaging (Bragg-CDI) was employed. Furthermore, synchrotron radiation X-ray diffraction (SXRD) combined with multi-component Rietveld analysis was used to quantify SGR volume fractions over a temperature range of 300–800 K. The analysis revealed that SGRs consistently occupied more than 50% of the total volume, significantly exceeding those observed in systems with a 300 nm core [4, 5]. These findings demonstrate that downsizing the BT core substantially expands the SGR, leading to improved dielectric performance in lead-free ferroelectric nanocomposites. |
