Effect of the A/B ratio on the microstructures and electrical properties of (Ba0.95±xCa0.05)(Ti0.82Zr0.18)O3 for multilayer ceramic capacitors with nickel electrodes

The microstructures and electrical properties of the perovskite-type (Ba0.95±xCa0.05)(Ti0.82Zr0.18)O3 oxides with various A/B ratios were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) with an energy-dispersive X-ray spectrometer (EDS). XRD results reveal that a second phase of Ba6Ti17O40 was formed when the A/B ratio was lower than 0.9956. TEM results show that liquid eutectic BaTiO3–Ba6Ti17O40 affects the sintering behavior and enhances grain growth; the grain size was significantly influenced when the A/B ratio changed from 0.9936 to 0.9976. The oxides’ electrical performances in multilayer ceramic capacitors (MLCCs) with nickel electrodes were closely related to the A/B ratio of the powder. It was found that with decreasing A/B ratio, the maximum permittivity was increased due to a larger grain size, and the Curie point shifted to a higher temperature, which resulted in higher permittivity at room temperature. The highly accelerated life test (HALT) shows that the reliability performance became worse with a decreasing A/B ratio due to the formation of the second phase Ba6Ti17O40 at the grain boundary.