Material Design for High Strength NTC Thermistor Ceramics

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.