Formation of Core-Shell Structure of BaTiO3 Grains in MLCC

To understand the formation of core-shell structure in BaTiO3 (BT) grains in multilayer ceramic capacitors, specimens were prepared with BT powders mixed with Y and Mg, and their microstructures were investigated in terms of scanning electron microscopy, x-ray diffractometry, and transmission electron microscopy. Compared to BT without Y and Mg, the addition of additives inhibited growth of the BT grains. Microstructural investigation showed that Y dissolved easily in BT lattice to a certain depth inside of the grain whereas Mg tended to stay at grain boundaries rather than to be incorporated into BT. It was considered that in case of Y and Mg addition in a proper ratio, Y could play a dominant role in the formation of shell leading to a slight dissolution of Mg in the shell. Next, the effects of ball-milling condition on the core-shell formation were studied. As the ball-milling period increased, the milled powders did not show a significant change in size distribution but an increase of residual strain which was attributed to the milling damage. The increase in milling damage facilitated the shell formation leading to the increased shell portion in the core-shell grain and, in turn, the deteriorating dielectric property.