Microwave absorbing materials have attracted much attention
in
solving electromagnetic interference and pollution problems. Hierarchical
cobalt selenides have been obtained through a facile selenization
annealing process. The as-prepared samples exhibit distinct reflection
losses (RL) and frequency responses via
tailoring their crystalline configurations, with excellent absorption
in Ku, X, or C band. All of the samples show RL greater than or near −50 dB with effective bandwidths
more than 4 GHz, indicating that they may serve as high-efficient
and frequency-tunable microwave absorbers. Especially, the sample
annealed at 400 °C shows a competitive RL of −62.04 dB at 9.92 GHz with a thickness of 2.25
mm; meanwhile, its effective absorption bandwidth reaches 5.36 GHz
with a thickness as small as 1.56 mm. The cobalt selenides as microwave
absorbers exhibit a promising prospect applied in complex electromagnetic
environments.