Microstructure Study of BaTiO_3-Ho_2O_3-MgO-SiO_2-Based Ceramics Using Convergent Beam Electron Diffraction Analysis

摘要

The mechanism of Curie temperature (T_c) elevation in BaTiO_3-Ho_2O_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.