**4. Summary**

samples have a smaller grain size, resulting in a decrease in the time between electron scattering events of charge carriers and thus increasing the resistivity [36]. In conclusion to this, SPS has potential superiority on synthesis high temperature NTC ceramic materials.

**Figure 8.** SEM images of the SPS-sintered *x*MgAl2O4-(1-*x*)YCr0.5Mn0.5O3 composite ceramics: (a) *x*=0.1; (b) *x*=0.4; (c)

**Figure 9.** Temperature dependence of electrical resistivity *ρ* of the samples 0.4MgAl2O4-0.6YCr0.5Mn0.5O3 sintered by

*x*=0.6 [12].

32 Sintering Techniques of Materials

conventional sintering (CS) and SPS [12].

The fundamentals, applications of spark plasma sintering to thermistor ceramics are reviewed in this chapter. For thermistor ceramics, the advantages of spark plasma sintering against traditional sintering are as follows: (1) Faster heating rate decreases the sintering time by using spark plasma sintering, and thus saving energy than traditional sintering; (2) Spark plasma sintering can ensure ceramics with high density and small grain at a low sintering temperature and a short sintering period. What's more, spark plasma sintering has shown significant advantages in the fabrication of YCrO3 perovskite-based thermistor ceramics and provides an efficient mean for the study of the conduction mechanism of NTC thermistors.

In the past years, there have had a significant developments and advances regarding to the spark plasma sintering of ceramics. However, the fundamental theory of spark plasma sintering is not fully understood, and also needs massive fundamental research and practical innovation to perfect. It can be forecasted that there is a great future for the successful commercialization of spark plasma sintering in ceramic preparation.
