The Effect of MgO and Rare-Earth Oxide on Formation Behavior of Core-Shell Structure in BaTiO₃

The formation mechanism of the core-shell structure of a BaTiO 3 (BT)–MgO–Ho 2 O 3 -based system was studied. Mg reacted with BT at low temperatures and showed poor diffusivity compared with Ho. The core-shell structure was considered to be formed by the suppression of the diffusion of Ho into the core region by Mg. Also, replacement modes of Mg and Ho in perovskite were investigated. Lattice parameters were determined at temperatures higher than the Curie temperature in order to avoid crystal structure change. It was confirmed that Mg dissolved in Ti site, and Ho dissolved in both Ba and Ti sites. This indicates that Mg ions act as acceptors and Ho ions act as both donors and acceptors in the shell phase.