Shrinkage Behavior and Diffusion in Ni-based Internal Electrodes with Additional Amount and Particle Size of BaTiO[sub 3] Additive

Abstract

The effect of additional amount and particle size of BaTiOs additive on shrinkage behavior and inter-diffusion in Ni-based internal electrodes has been investigated, in order to reduce the large shrinkage mismatch between the internal electrode and the dielectric layer and to control the thermal and/or residual stresses in multilayer ceramic capacitors (MLCCs). Ni powder of 100-500 nm and two kinds of BaTiOs powders of 100 and 200 nm were used as matrix and additive, respectively. The Ni and BaTiOs powders were mixed with volume ratios of 95:5, 90:10, 85:15, respectively, and then cold-isostatic pressed. The shrinkage of starting materials and each composite was measured in a range of 700-1300°C with 150°C interval in H2/Ar atmosphere, using ASTM standard method. Diffusion phenomena at interface of Ni/BaTiOs composites with 85:15 and 90:10 volume ratios were investigated using SEM, EDX, and TEM. The particle size affects the shrinkage behavior in relatively low temperatures below 1000°C, showing a turning point at that temperature. The final shrinkage of composites is matched with that of bulk BaTiOs of smaller particle size, independent of additional amount of BaTiOs additive. A reaction layer of about 1000 nm wide is observed at the interface between the Ni and BaTiOs powders in the composite of 85:15 volume ratio. The quantitative amount of elemental Ni diffused into the BaTiOs is about 9.7 mass% in the composite of 90:10 volume ratio, without another phase seen in the Ni.