Effect of the A/B ratio on the microstructures and electrical properties of (Ba_0.95±xCa_0.05)(Ti_0.82Zr_0.18)O₃ for multilayer ceramic capacitors with nickel electrodes

The microstructures and electrical properties of the perovskite-type (Ba_0.95±xCa_0.05)(Ti_0.82Zr_0.18)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.