Effects of Microstructure on the Curie Temperature in BaTiO3–Ho2O3–MgO–SiO2 System

In response to the demand for multilayer ceramic capacitors (MLCCs) with stable capacitance in a wide temperature range, a material with high Curie temperature ( T c ) has recently been being developed. In this study, we investigated the effects of microstructure on the T c for the BaTiO 3 –Ho 2 O 3 –MgO–SiO 2 system with various Ho and Si contents. As the Ho/Si ratio increased, the secondary phase (Pyrochlore) increased; further, the tetragonality of the BaTiO 3 phase at 125 °C increased, and the T c shifted toward higher temperatures. A transmission electron microscope equipped with energy dispersive X-ray spectrometer (TEM–EDS) analysis revealed that the core-shell structure is the key to understand this T c shift: a thin shell with a high concentration of Ho was the most promising microstructure for a high- T c material in this composition system. We discussed the mechanism of the T c shift from the viewpoints of both microstructure and crystal structure.