## 3 Results and Discussion
The use of sintering aids with different rare earth/alkaline earth ratios can achieve phase transformation and densification regulation, thereby controlling the microstructure of Si\({}_{3}\)N\({}_{4}\) ceramics, which is particularly important for improving the mechanical and electrical properties of Si\({}_{3}\)N\({}_{4}\) ceramics [21]. Figure 2: Etched surface, sectional microscopic morphology, and some EDS spectra of Si\({}_{3}\)N\({}_{4}\) ceramics. (**a**,**b**) 1825-5Y-92 SN, (**c**,**d**) 1825-5Y-90 SN, (**e**,**f**,**i**,**j**) 1825-6.25Y-90 SN, (**g**,**h**) 1825-6.8Y-90 SN, and (**k**,**l**) 1825-7.5Y-88 SN. The distribution characteristics of the direct current electric field are closely related to the conductivity characteristics of insulating materials, and the conductivity and temperature characteristics of insulating materials dominate the distribution of the electric field in insulating structures. The volume resistivity change characteristics of Si\({}_{3}\)N\({}_{4}\) ceramic materials under a field strength of 1 kV/mm in the temperature range of 298-353 K were tested using the three-electrode method, as shown in Figure 3. The volume resistivity of Si\({}_{3}\)N\({}_{4}\) ceramic composite materials at room temperature (298 K) and under an electric field of 1 kV/mm was greater than 10\({}^{14}\)\(\Omega\cdot\)m. The room temperature resistivity of sample 1825-5Y-92 SN was the largest, 7.33 \(\times\) 10\({}^{14}\)\(\Omega\cdot\)m, significantly better than the value of 10\({}^{11}\)\(\Omega\cdot\)m obtained by [PERSON], [PERSON] et al. [18]. With the increase in sintering aid content, the resistivity of Si\({}_{3}\)N\({}_{4}\) ceramic composite materials gradually decreased, while the proportion of sintering aid had little effect on resistivity. With the increase in temperature, the decreasing trend of the volume resistivity of Si\({}_{3}\)N\({}_{4}\) ceramics gradually slowed down. Compared with the values at room temperature, the volume resistivity of the five samples was between 35% and 50% at 80 \({}^{\circ}\)C. Sintering aids were beneficial to improving the temperature stability of Si\({}_{3}\)N\({}_{4}\) ceramics. The volume resistivity was the most stable when the aid content was 12%, with a room temperature volume resistivity of 4.40 \(\times\) 10\({}^{14}\)\(\Omega\cdot\)m and an 80 \({}^{\circ}\)C volume resistivity of 2.13 \(\times\) 10\({}^{14}\)\(\Omega\cdot\)m, with a remaining rate of 48.4%. The main reasons are that the doping of functional ions, such as Y\({}^{3+}\), can introduce weakly bound ions and lower the potential barrier conductivity levels in the material and the formation of Y\({}_{2}\)SiAlO\({}_{5}\)N crystalline phase reduces the carrier concentration and reduces the influence of temperature changes on the volume resistivity of the material. When the sintering aid content was 10% and the ratio of Y\({}_{2}\)O\({}_{3}\) to Al\({}_{2}\)O\({}_{3}\) was 5:2.35, the volume resistivity had the best temperature stability at 47.4%, decreasing from 5.59 \(\times\) 10\({}^{14}\)\(\Omega\cdot\)m at room temperature to 2.65 \(\times\) 10\({}^{14}\)\(\Omega\cdot\)m. In addition to the aforementioned reasons, this method also reduces the grain size of silicon nitride ceramics and prolongs the carrier migration path. In contrast, the volume resistivity of epoxy resin/Al\({}_{2}\)O\({}_{3}\) composite materials used in current ultra-high-voltage transmission and transformation equipment decreases from 10\({}^{14}\)\(\Omega\cdot\)m to 10\({}^{12}\)\(\Omega\cdot\)m when the temperature rises from 298 K to 353 K, with a decrease of more than 99%. It is obvious that Si\({}_{3}\)N\({}_{4}\) ceramics have better temperature stability and significant advantages in improving the distribution characteristics of the electric field under temperature gradients in practical applications. Figure 3: Relationship between volume resistivity of Si\({}_{3}\)N\({}_{4}\) ceramic materials and temperature.