Abstract
To meet recent requirements for high-performance dielectric capacitors, we have attempted to develop new boundary layer (BL) ceramic capacitors consisting of conductor grains epitaxially covered with insulator boundary layers to improve their dielectric breakdown strength. First, we attempted to synthesize conductor-insulator core–shell particles with epitaxial interfaces, because the desired BL capacitors can be prepared by assembling these core–shell particles. One of the conductive perovskite oxides, lanthanum nickel oxide (LaNiO3, LN), was selected as the conductor layer, and bismuth potassium titanate [(Bi1/2K1/2)TiO3, BKT], which has a similar lattice constant to LN, was selected as the insulator layer. LN nanoparticles synthesized by the sol–gel method were mixed with the titanium oxide (TiO2) and bismuth nitrate [Bi(NO3)3] in the KOH aqueous solution, and hydrothermal treatment was performed at 160°C. LN–BKT powders could be obtained in the presence of the Bi and Ti sources without decomposition of LN. This fact suggests that the BKT coating layers formed initially on the surface of the LN nanoparticles and prevented a decomposition reaction of LN in the KOH aqueous solutions. The formation of a core–shell structure in the LN–BKT powders was confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy observation revealed epitaxial growth of a BKT shell layer on the LN core nanoparticles.
