Solubility of La–Mg and La–Al in BaTiO 3

Abstract

For the design of the multilayer ceramic capacitors (MLCs) with core-shell structure, the solubility modes of La–Mg and La–Al into BaTiO 3 were clarified as a function of composition based on the lattice parameters' change. The lattice parameter was determined based on a cubic system at a higher temperature than the Curie temperature in order to avoid the crystal structure change. On the BaTiO 3–La 2O 3–MgO system, there were three substitution modes. In the region where x was small on the (Ba 1− x La x )(Ti 1− x/2 Mg x/2 )O 3, Mg ions preferentially dissolved into B site of BaTiO 3, but in the region where x was large, both La and Mg ions dissolved into A and B site, respectively. On the other hand, on the BaTiO 3–La 2O 3–Al 2O 3 system, La and Al ions partially replaced Ba and Ti ions, respectively, according to pre-determined replacement formula (Ba 1− x La x )(Ti 1− x Al x )O 3. The solubility range of La into BaTiO 3 was wider than that of Dy or Ho which make the core-shell structure. So, the dielectric materials composed of BaTiO 3 containing La are not fitted to form the core-shell structure. Therefore, considering ionic radius of rare earth element, BaTiO 3 containing rare earth elements whose ionic radii are much smaller than that of Ba is fitted to form the core-shell structure.