Papers by Author: Hideaki Niimi

Abstract: Electric potential mapping of degraded dielectric layers of multilayer ceramic capacitors (MLCCs) was carried out using Kelvin probe force microscopy in order to clarify their degradation mechanism under conditions of an accelerated lifetime test condition. In the cross sections of the degraded and as-prepared dielectric layers, a significant electric field concentration was found in the vicinity of the anode of the degraded dielectric layer, in contrast to a homogeneous concentration found throughout layers of the samples before the accelerated lifetime test.

Abstract: Various factors were investigated to decide the mechanical properties of (Mn1–xNix)3O4 ceramics, that are typical composition systems of NTC (negative temperature coefficient) thermistors. The strength of NTC thermistor ceramics can be improved by designing the material so that the compressive stress may remain at the surface of the ceramics. At high temperature, the thermal expansion coefficient of a rock salt phase segregated internally ceramic increases over that of the spinel phase, further, on the surface of the ceramics, this compressive stress remains below room temperature. Moreover, it was confirmed that the stress analysis result by the FEM corresponded well with the stress measurement result on the surface of the ceramics measured by μ -XRD.