## 3 Results
### Electrical Properties of the Semiconductive Shielding  
Figure 8 shows that curve of resistivity versus temperature for the semiconductive layer containing different mass fractions of LSC. Figure 9 shows the resistivity curve of semiconductive materials with different LSC contents at 383 K. It can be seen from Figure 9 that at 383 K, the resistivity of semiconducting shielding material without LSC doping is 798 \(\rho\)/\(\Omega\)-cm and when the LSC doping amount is 1 wt%, the resistivity is 128.5 \(\rho\)/\(\Omega\) cm, decreased by 83.9%. Some researchers have added SrFe\({}_{16}\)O\({}_{19}\) to semiconductor shielding materials and tested their resistivity. The resistivity of semiconductive materials with SrFe\({}_{16}\)O\({}_{19}\) doping of 1 wt% and 5 wt% is similar to that without SrFe\({}_{16}\)O\({}_{19}\) doping. When the doping amount of SrFe\({}_{16}\)O\({}_{19}\) is 30 wt%, the resistivity of semiconductive materials is more than 10\({}^{3}\) at 383 K [26]. We can see that the resistivity demonstrates a slow rising tendency with temperature before the temperature is below 343 K. Meanwhile, there is a huge transition in the resistivity value of the semiconductive composites without added LSC after the temperature exceeds 343 K. In other words, the semiconductive layer without added LSC possesses a significant PTC effect. Since the electrical conductivity of the LSC increases with increasing temperature, the semiconductive layer to which LSC is added still has good electrical conductivity at high temperatures. It can be seen from Figure 9 that at 383 K, the resistivity of semiconductive materials with 1 wt% LSC doping is greatly reduced compared with that without LSC. Therefore, the addition of LSC can improve the PTC effect of the semiconductive composites so that it still meets the resistivity requirements of the semiconductive layer at high temperatures. In particular, the semiconductive layer with a 1% LSC presents good electrical conductivity at high temperatures. This might be attributed to the distortion of the crystal structure of Sr-doped LaCoO\({}_{3}\), the lattice spacing becomes larger, and the amount of O vacancies increases, providing more conductive channels for carrier transport.  
Figure 6: SEM of sections of non-semiconducting shielding materials with different LSC contents: (a) 0 wt% LSC; (b) 1 wt% LSC; (c) 5 wt% LSC.  
Figure 7: Transmission electron microscopy (TEM) micrographs of the semiconductive materials with different LSC contents: (a) 0 wt% LSC; (b) 0.5 wt% LSC; (c) 3 wt% LSC.  
The formula for calculating the strength of the polymer's positive temperature coefficient:  
\[\alpha=\lg\frac{\rho_{v(\text{max})}}{\rho_{v(\text{min})}}\]  
The calculated PTC strengths of semiconductive composites with LSC doping contents of 0%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt% and 5 wt% were 1.47, 0.96, 0.91, 0.99, 0.95, 1.02. Compared with the PTC strength of the semiconductive materials without LSC, the PTC strength of the semiconductive materials with 1 wt% LSC content decreased by 38.1%, which indicated that the addition of LSC has a significant weakening effect on the PTC effect of the system, which is related to the increase in the conductivity of the ionic conductor with the increase in temperature. As the temperature increases, the number of carriers in the LSC increases, and the mobility of the carriers increases. Therefore, the PTC effect of the LSC/CB/LDPE/EVA composites is weaker. With the increase in LSC content, the PTC strength of nanocomposites decreases first and then increases. Because of the agglomeration of LSC in semiconductive materials, part of the carbon black conductive network in the composites is disconnected, thus, the PTC strength of semiconductive materials increases when LSC content is high.  
Figure 8: Resistivity of the semiconductive composites with different mass fractions of LSC as a function of temperature.  
Figure 9: Resistivity curves of semiconductive materials with different LSC contents at 383 K.