The Mechanism of Core/Shell Structure Formation During Sintering of BaTiO ₃ ‐Based Ceramics

The mechanism of core/shell formation during sintering in B a T i O 3 ‐based systems was studied in ( M g, Y )‐doped B a T i O 3 . The effect of ball milling time on core size and shell thickness was first observed. The core size was similar irrespective of ball milling time whereas the shell thickness increased with increasing ball milling time. The measured powder size after ball milling suggested that the cores were from the larger B a T i O 3 particles and the shells formed via dissolution of smaller particles and precipitation of dissolved material, in contrast with the interpretation of the results of a previous investigation. To identify the core/shell formation mechanism, bi‐layer samples with different chemical compositions, 94 B a T i O 3 –2 Y 2 O 3 –2 M g O –2 S i O 2 (mol%) ( BT – YMS ) and 98 B a T i O 3 –2 S i O 2 (mol%) ( BT – S ), and different grain sizes were prepared. The morphology of the newly formed shell layer and the shape of an {111} twin across the interface between a core and a shell confirmed that the formation mechanism of the core/shell structure during sintering is the dissolution and precipitation of material rather than solid‐state diffusion of solutes into B a T i O 3 .