## 3 Results and Discussion
### Effects of Coupling Agent on the Dielectric Properties of PZT-PVDF  
Figure 3 showed the dielectric properties versus volume percent of KH-570 in PZT/PVDF composites. The test frequency was at 1 kHz under the condition of room temperature. As can be seen, as the content of KH-570 increased, the relative dielectric constant \(\varepsilon_{r}\) of PZT-PVDF composites decreased gradually. Without silane coupling agent KH-570, the relative dielectric constant \(\varepsilon_{r}\) of PZT-PVDF composites was 54.75. When the content of the KH-570 was 2.0%, the relative dielectric constant \(\varepsilon_{r}\) was reduced to 36.38, which was reduced by 33.55%. Meanwhile, the dielectric loss tan \(\delta\) of the composites increased with the increased content of KH-570. By analysis, after PZT-PVDF composites were treated by KH-570 coupling agent, the infiltration effect of the ceramic phase in the polymer phase was improved, and the structures of the PZT-PVDF composites became more compact, and the porosity was decreased, all of which enhanced the dielectric constant of the PZT-PVDF composites to some extent. What cannot be overlooked was that a layer of insulation was formed on the surface of the ceramic phase which was caused by PVDF molecular chain and KH-570 wrapped. The greater the KH-570 content was, the greater the insulating layer thickness was. However, the dielectric constant of the insulating layer was smaller than the ceramic phase and polymerization phase. Therefore, the greater the content of KH-570 there was, the smaller the values of the dielectric constant the PZT-PVDF composites had. Simultaneously, multi molecular layers which were caused by KH-570 to improve the ceramic phase interface, declined the uniformity degree of the PZT-PVDF composites interface and increased the relaxation polarization current. Finally, all these lead to an increase of the dielectric loss tan \(\delta\) of PZT-PVDF composites.  
Figure 4 showed the dielectric constant versus volume percent of NDZ-101 in 0.5 PZT/0.5 PVDF composites. The test frequency was at 1 kHz under the condition of room temperature. As can be seen from Figure 4, as the NDZ-101 content was increased, the relative dielectric constant \(\varepsilon_{r}\) of the PZT-PVDF increased slightly. In particular, when the content was 0.5%, the dielectric constant \(\varepsilon_{r}\) was increased from the initial 64.75 to a maximum of 69.29, i.e., it increased only by 7.01%. However, as the NDZ-101 continued to be increased, the relative dielectric constant \(\varepsilon_{r}\) of the PZT-PVDF composites decreased. Simultaneously, with the increase of content, the dielectric loss tan \(\delta\) of the PZT-PVDF  
Figure 3: Effects of KH-570 on the dielectric properties of the PZT-PVDF.  
composites showed an increasing trend. When the content was 0, the dielectric loss tan \(\delta\) was 0.037. When the content was 2%, the dielectric loss reached 0.1175. By analysis, during the preparation of piezoelectric composites, adding a certain amount of NDZ-101 improved the two-phase interface state, but the effect was not obvious. Meanwhile, NDZ-101 can lower the dielectric properties of PZT-PVDF. In contrast, the dielectric loss tan \(\delta\) of the PZT-PVDF composites increased rapidly. This was because NDZ-101 produced an accumulation phenomenon and reduced the interfacial strength greatly.