Role of yttrium and magnesium in the formation of core-shell structure of BaTiO3 grains in MLCC

To understand the contribution of additive elements to 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. The additives inhibited growth of the BT grains, particularly leading to a much reduced sinterability for Y addition. 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, added 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.