Morphology-controlled synthesis and excellent microwave absorption performance of ZnCo2O4 nanostructures via a self-assembly process of flake units

Abstract

Pure dielectric microwave absorbers with strong attenuation capability and wide-band response become a challenge for efficient electromagnetic wave energy absorption. Herein, a series of ZnCo₂O₄ hierarchical structures with superior absorption performance have been achieved by tuning their surface architectures from ball-, hydrangea- to cabbage-, and pineapple-like morphologies. A facile one-step synthesis strategy using a self-assembly process with ZnCo₂O₄ crystalline flakes as structural units was proposed. The deionized water solution and urea addition were found to critically determine the formation of our unique cabbage-like ZnCo₂O₄ self-assembled morphology. The wide band and distinct absorption was dominantly contributed from dielectric ZnCo₂O₄ flakes, which could be furthermore adjusted by the above-mentioned morphologies. Due to its abundant void volume stacked by flakes, the cabbage-like ZnCo₂O₄ demonstrated the best absorption performance where the RL_max reached −36.33 dB at 9.5 GHz with an efficient bandwidth of 5.11 GHz (RL < −10 dB, 11.17–16.28 GHz). Adjusting the simulating thickness from 1 to 5 mm, the bandwidths range from 5.8 to 18 GHz. This unique structure has the polarization, conduction loss and strong dissipation capability resulting from the high density of accumulated charges trapped by the flake gap, confirmed by the analysis of electromagnetic parameters and electronic holography. It is expected that the self-assembled ZnCo₂O₄ microsphere might shed new light on the design of novel microwave absorption materials.