Strain gradient across the heteroepitaxial interface in a BaTiO₃/KNbO₃ core-shell nanocomposite particle revealed by synchrotron radiation X-ray diffraction

Abstract We synthesized BaTiO₃–KNbO₃ (BT–KN) core–shell nanocomposite particles, in which a KN shell epitaxially grows on a BT nanoparticle to form a shell around the BT core. To investigate the relationship between interfacial lattice strain and dielectric properties, we prepared BT nanoparticles with a reduced grain size of 80 nm and analyzed their structural features using synchrotron radiation X-ray diffraction over a wide temperature range (300 –800 K). Multi-component Rietveld refinement revealed that more than half of the particle volume exhibited lattice distortion, forming an extended structure gradient region (SGR) induced by the heteroepitaxial interface. The SGR volume fraction was largest at 300 K, where the tetragonal BT core was in contact with the orthorhombic KN shell. These results demonstrate that reducing the core size significantly increases the spatial extent of the SGRs, providing a promising strategy to tailor dielectric properties through nanoscale interface engineering.