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 BaTiO3-Ho2O3-MgO-SiO2 system with various Ho and Si contents. As the Ho/Si ratio increased, the secondary phase (Pyrochlore) increased; further, the tetragonality of the BaTiO3 phase at 125 degrees 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.