Nitrogen content dependent microwave absorption property of nitrogen-doped SiC materials annealed in N2: Opposing trends for microparticles and nanowires

Nitrogen-doped SiC microparticles (SiCp) and SiC nanowries (SiCNWs) with different nitrogen contents were successfully synthesized by a simple and effective method, in which SiCp and SiCNWs were directly annealed in N2 at 1500 °C with different holding times to adjust the contents of nitrogen for the first time. The nitrogen content of N-doped SiCp and SiCNWs increased with holding time, from 2.91 at.% and 3.05 at.% for 1 h to 5.05 at.% and 5.25 at.% for 4 h. The size of N-doped SiCp and SiCNWs was larger than that of pristine SiCp and SiCNWs, while the size tended to increase firstly and then decrease. The results of dielectric parameters showed that both real part ε′ and imaginary part ε″ of permittivity of the samples increased greatly with increasing N contents in most frequency range, while two opposing trends for nitrogen content dependent microwave absorption property of N-doped SiCp and SiCNWs were observed. The electromagnetic (EM) wave absorption capability of N-doped SiCp was significantly improved with increasing nitrogen content compared with fully permeable wave pristine SiCp, and the minimum reflection loss (RLm) and maximum effective absorption bandwidth (EAB) could be up to −33.5 dB and 4.4 GHz, respectively. The EM wave absorption performance of N-doped SiCNWs exhibited a decreasing tendency with increasing nitrogen content, and the RLm was decreased from −57 dB for pristine SiCNWs, to −51.2 dB for SiCNWs with 3.05 at.% N, and to −29.3 dB for SiCNWs with 5.25 at.% N. Moreover, if the experimental process in present study was decomposed into heat-treatment and N-doping, the heat-treatment played extremely negative effect on the EM wave absorption performance of samples, while N-doping still had positive impact on the EM wave absorption performance. It is believed that the current work will provide a new insight into the fabrication of SiC materials with fascinating properties by doping.