Dielectric Properties And Microwave Absorption Of Dielectric Materials At Elevated Temperature

High efficiency and light weight are two key factors which can significantly influence the practical application of electromagnetic(EM) wave absorption materials, which have been widely applied in civil, commercial, military and aerospace vehicles in service in extreme environments. Therefore, the development of multiple polarization and improvement of the conductivity is very important to enhance the dielectric properties and microwave absorption and thereby broaden the practical applications. In this paper, we investigate the dielectric properties of SiC, nano Ni/SiC composite material, nanorings NiO/SiC composite material, multiferroic BiFeO3 nanoparticles and Co-doping Bi FeO3 nanoparticles. We analyze their dielectric response behavior and the related factors. We study their microwave absorption and their energy loss mechanism.(1) The dielectric properties of SiC are investigated in the temperature range of 373-773 K at gigahertz range(8.2-12.4GHz). The complex permittivity ε and the loss tangent tgδ exhibit frequency-dependent characteristics, and they also show temperature-dependent characteristic. From the Cole–Cole plots, it can be seen both the relaxation and electrical conductance affect the dielectric properties at high temperature. First principle calculations are employed to analyze the electronic structure of SiC, which infer the influence of relaxation and conductance on dielectric behaviors. The reflection loss RL peak is below-10 dB in temperatures of 373–773K with the sample in thickness 2.1mm. More importantly, the microwave absorption coupled with widening effective absorption bandwidth demonstrates positive temperature effects on the absorption with the increasing temperature.(2) The dielectric properties and microwave absorption of Ni-decorated SiC powders are investigated in the temperature range of 373–673 K at frequencies of 8.2–12.4 GHz(X-band). Ni-decorated SiC powders are fabricated by using an improved solution chemical method. Compared to the naked SiC, the complex permittivity and loss tangent of Ni-decorated SiC are significantly improved in the investigated frequency and temperature ranges. Strong temperature-dependent loss tangent associated with the hopping conductance between Ni nanoparticles in the modified layers is observed in the Ni-decorated SiC. Calculation of the microwave absorption shows that much enhanced absorption performance can be observed in the Ni-decorated SiC. Increased microwave absorption coupled with widened effective absorption bandwidth demonstrates positive temperature effects on the absorption performance.(3) The dielectric properties and microwave absorption are investigated in the range from 373 to 773 K and X band. NiO nanorings on SiC, a novel hierarchical architecture, were fabricated by a facile two-step method. The imaginary part and loss tangent increase more than four times and three times with increasing temperature, respectively. The architecture demonstrates multi relaxation and possesses high-efficient absorption. The reflection loss exceeds-40 dB and the bandwidth covers 85% of X band(approximately-20 dB). The synergistic effect between multi relaxation and conductance is beneficial to the microwave absorption.(4) The dielectric properties and microwave absorption of BiFeO3 and Co doped BiFeO3 are investigated in the frequency range from 2 to 18 GHz. The dielectric properties and the magnetic properties have three relaxations in the investigated frequency range. The microwave absorption exhibits characteristic of multi-band absorption with strong absorption peaks at S band, X band and Ku band. The minimum reflection loss of Co doped BiFeO3 can reach to-35.8dB. The microwave absorption of Co doped BiFeO3 is multi-band and efficient.