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

概要

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In response to the demand for multilayer ceramic capacitors (MLCCs) with stable capacitance in a wide temperature range, a material with high Curie temperature $(T_{\text{c}})$ has recently been being developed. In this study, we investigated the effects of microstructure on the $T_{\text{c}}$ 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 °C increased, and the $T_{\text{c}}$ 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 $T_{\text{c}}$ shift: a thin shell with a high concentration of Ho was the most promising microstructure for a high-$T_{\text{c}}$ material in this composition system. We discussed the mechanism of the $T_{\text{c}}$ shift from the viewpoints of both microstructure and crystal structure.
2007-10-30