Silica Additions and the Performance of PTC Thermistors
A series of PTC thermistors, based on BaTiO3, doped with Ca, Mn and Y, were prepared with additions of SiO2 at levels of 0, 1, 2 and 3 at. %. The effect of the SiO2 additions and cooling rate on microstructural development and bulk performance were characterised using a combination of SEM, EBSD, and R-T experiments. It was found that the addition of SiO2 increased grain size marginally, and decreased sample density by reducing the amount of grain-grain contact. The addition of SiO2 also modified the distribution of grain boundary types by systematically decreasing the proportion of low-Σ grain boundaries within the microstructure. Electrical behaviour was modified by adding SiO2 or increasing the sample cooling rates; in both cases there was an increase in ρ25 and a decrease in ρmax, with ρmax also being displaced to higher temperatures.
C. Leach et al., "Silica Additions and the Performance of PTC Thermistors", Advances in Science and Technology, Vol. 45, pp. 2362-2370, 2006