Microstructure Study of BaTiO 3 –Ho 2 O 3 –MgO–SiO 2 -Based Ceramics Using Convergent Beam Electron Diffraction Analysis

The mechanism of Curie temperature ( T C ) elevation in BaTiO 3 –Ho 2 O 3 –MgO–SiO 2 -based X8R ceramics was investigated in terms of the variations in the lattice parameters of individual grains using convergent beam electron diffraction analysis. Three sintered samples with different values of T C depending on Ho and Si concentrations were observed to have a lattice parameter gradient even in the grain core of almost pure BaTiO 3 as well as in the grain shell with a chemical gradient. Interestingly, the sample with a higher T C exhibited a flatter gradient of the lattice parameter in the grain core, implying less prominent development of compressive stress. It is suggested that the incorporation of a high Ho concentration into the grain shell has significant effects on the relaxation of the compressive stress mainly arising from ferroelectric phase transition. This results in the shifting of T C toward a higher value.