Novel binary cobalt nickel oxide hollowed-out spheres for electromagnetic absorption applications

Novel binary cobalt nickel oxide Co_1.29Ni_1.71O₄ hollowed-out spheres have been successfully synthesized via a facile hydrothermal method with a further calcination process. The phase, crystal structure, morphology, and electromagnetic (EM) and EM wave absorption properties were characterized in detail. We find that as the temperature increases, the ionic mobility in the spinel structure will increase, leading to lattice disorder and an increase in the concentration of oxygen vacancy, which will improve the dielectric loss and EM wave absorption capacity of the material. The minimum reflection loss (RL_min) of the sample calcined at 500 °C reached up to −50.7 dB with a matching thickness (d) of 1.6 mm, and the corresponding effective absorption bandwidth (f_E, RL < −10 dB) was 4.84 GHz. The sample calcined at 550 °C also showed excellent EM wave absorption properties, and the corresponding RL_min, f_E, and d were −44.5 dB, 5.13 GHz, and 2.0 mm, respectively. We are confident that the spinel Co_1.29Ni_1.71O₄ will become an excellent candidate for a new generation of high-efficiency EM wave absorbing material.