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With the more serious threats from complex electromagnetic environments, composites composed of conductive or semiconductive fillers and polymeric matrices could exhibit excellent nonlinear I-V characteristics, and have drawn significant attention in the field of overvoltage protection. In this research, graphene nanoplatelets (GNPs) are decorated by ZnO and mixed into an epoxy resin (ER) matrix via solution blending to prepare composites. A characterization analysis and the I-V measurement results of the GNPs/ER composites indicate that ZnO nanoparticles are well bonded with GNPs and exhibit obvious nonlinear I-V behavior under proper applied voltage with high nonlinear coefficients. The switching threshold voltage and nonlinear coefficients could be controlled by adjusting the weight ratio of GNPs and ZnO of the filler. Moreover, compared with the poor recoverability of pure GNP-filled ER in previous research, the GNP-ZnO/ER composites exhibited excellent reversibility of nonlinear I-V behavior under multiple repetitive I-V measurements. And compared with different composites, the sample with a 1:8 weight ratio of GO to Zn(Ac)2 presents the smallest variation of switching threshold voltage at 158 V, with a standard deviation of 1.27% from among 20 measurements, which indicates the best reversibility. Finally, the conducting mechanism of the reversible nonlinear I-V characteristic is investigated and analyzed.

Epoxy resin (ER)/micron-aluminum particles (MP) composites with different filling concentration of spherical particles were fabricated. The nonlinear conductive behavior of ER/MP composites under increasing applied voltage using the improved V-I method was investigated. Under sufficient high intensity applied constant voltage, the obvious conductive switching behavior of samples with volume fraction 12.7%, 16.9% and 18.9% was found. The conductivity of ER/MP composites increase up to 3–4 orders of magnitude when the conductor-insulator transition occurs. The switching threshold voltage decreases with the increase of volume fraction of MP in the composites. The results show that the ER/MP composites with conductive switching properties are of great potential application in electromagnetic protection of electron devices and systems.

Vanadium dioxide (VO₂) is a typical representative of strongly correlated electronic systems, which undergoes a reversible transition from the insulator phase to metal phase, induced by a certain threshold for each of temperature, electric field, illumination and pressure. The crystal structure of VO₂ will undergo a reversible transition from monoclinic structure to tetragonal rutile structure when the phase transition happens, which is considered as the microscopic mechanism of VO₂ metal-insulator transition (MIT). The conductivity of VO₂ can be increased by 2—5 orders of magnitude when the MIT is induced by electric field, which makes VO₂ possess good application prospects in the fields of restructurable slot antenna, terahertz radiation, intelligent electromagnetic protection materials, etc. Therefore, the reversible metal-insulator phase transition in VO₂, induced by electric field, has long been a research hotspot, which however, has been seldom reported. Firstly, in this paper, the changes of the crystal structure and energy band structure of VO₂ during MIT are introduced briefly. The methods of regulating the phase transition are given, including temperature control, bandwidth and band-filling control. Then, the important discovery and research progress of VO₂ MIT induced by electric field based on the research method, response time, critical threshold field and phase transition mechanism are summarized and reviewed comprehensively. The method of studying the VO₂ phase transition relates to its structure, including planar structure, three-terminal gated ?eld effect switch and sandwiched layer structure. The sandwich layer structure is more suitable for investigating the MIT characteristics of VO₂ in experimental stage because of its structural advantage of preparation and test. The response time of VO₂ MIT can be completed in nanoseconds, of which the substantial parameter has been revealed by many reports, also including the excellent reversibility of VO₂ MIT. The MIT critical threshold field of the VO₂ film can be tuned by element doping, coexistence of multivalent vanadium oxides and multiple physical field synergism effectively. The MIT mechanism of VO₂ induced by electric field has been proposed so far, which includes joule heating mechanism and pure electric field mechanism, and the latter is considered to be more likely to give a reasonable explanation. Finally, in the paper the current problems of the VO₂ MIT research and the near-future development direction of the VO₂ MIT materials are also pointed out.