Atsuyuki Nakano

Microwave Sintering Study of NiCuZn Ferrite Ceramics and Devices

Studies on the sintering behavior, including densification and grain growth of NiCuZn ferrite ceramics were carried out in a microwave field of 2.45 GHz. Compared to conventional sintering, the shrinkage curves of a NiCuZn ferrite system processed by microwave sintering were observed to have shifted towards approximately 100°C lower temperatures. From the analysis of shrinkage data, it was found that the effective activation energy for diffusion under the microwave sintering was lower than those controlled under conventional sintering. In addition, pressed toroidal inductors and multilayer chip inductors (MLCI) have also been sintered by the microwave processing. Although heating rate of the microwave sintering was faster than that of the conventional sintering, the microwave sintered samples were found to be without any visible cracks. The total sintering time was reduced significantly in comparison with the conventional sintering. In both the sintered toroidals and MLCI samples, comparable magnetic properties were obtained.

High Dielectric Constant Negative-Positive-Zero Dielectric Materials Based on (100-x)(La0.1Bi0.9)Ti2O7-xSrTiO3

Dielectric materials based on the solid solution system (100-x)( La0.1Bi0.9) Ti2O7–xSrTiO3 have been studied in order to obtain high performance capacitor materials. Compositions with temperature coefficient of capacitance as low as τ c<20 ppm and dielectric constant as high as 250 make them suitable for negative-positive-zero (NPO) capacitor designated applications. Using X-ray diffraction, a three-phase mixture of the two end members, SrTiO3, ( La0.1Bi0.9) Ti2O7, and a Bismuth-layer structure phase with only a limited amount of solid solution was observed. The low-temperature coefficient of capacitance was believed to be the result of the balancing of the positive and negative temperature coefficients characteristic of the three constituent phases.