Na_0.78CoO₂ as a novel microwave absorbing material

A novel microwave absorbing material, sodium cobaltates (Na_0.78CoO₂) was synthesized by solid-state reaction, which shows a good electromagnetic attenuate property. Because of preferential growth along the C axis, the Na_0.78CoO₂ powder reveals a typical lamellar structure. Theoretical calculations suggest that there is a minimum reflection loss (RL) around −51.7 dB at a frequency of 8.2 GHz in the composite with 50 wt% Na_0.78CoO₂ and 50 wt% paraffin when the thickness of the composite is about 2.41 mm. Moreover, its effective absorbing bandwidths (RL < −10 dB) are in a range from 12.5 to 15.6 GHz in the case of the sample thickness of around 1.5 mm. The electromagnetic attenuation mechanisms of the composite are relevant to conductive loss, multiple reflection loss, and dipole or interfacial polarization loss.