Preparation and dielectric properties of polyimide-based composites with Al-Nb co-doped SiO 2

Polyimide (PI) film have been synthesized and used extensively in energy transmission, wind power generation, new energy vehicles, lidar, and high-power weapons, et al. Nevertheless, it is still challenge to further improve the breakdown strength and dielectric constant of PI film. After the powders of Al_0.5xNb_0.5xSi_1-xO₂ (NASO (x mol%)) have been fabricated, it was analyzed that the effect of doping elements Al³⁺ and Nb⁵⁺ on the surface chemistry and microstructure of the NASO powder. And then a small amount of NASO powder was polymerized in situ with PI matrix material, and the effects of NASO on dielectric properties and breakdown strength of the NASO/PI composites were analyzed. The results showed that the introduction of the doping elements Al³⁺ and Nb⁵⁺ favors could be conductive to the formation of oxygen vacancies on the surface of the NASO particle, which improved the surface activity and chemical reactivity of the NASO particle. The PI matrix can efficiently capture additional charges and enhance the insulating characteristics of the NASO/PI composite by properly doping NASO fillers with specific defect concentrations. In the results the breakdown strength of 1 vol% NASO (1 mol%)/PI composites reaches 334.38 kV/mm, which is a 19.6% higher than that of PI. Because the traps in the fillers capture and suppress the carrier transport to enhance the insulating properties of the composites. This work offers a novel synthesis method to simultaneously produce polymer dielectrics with high insulation and high polarization.