Enhanced microwave absorption and electromagnetic shielding property of (1-x)K_0.5Na_0.5NbO₃ ~ xAl₂O₃ nano-ceramics

(1-x) K_0.5Na_0.5NbO₃ ~ xAl₂O₃ (x = 0, 0.2, 0.4, 0.6) ceramics were prepared via a traditional solid-state reaction method. The phase structure, micro-morphology, dielectric properties and electromagnetic properties of ceramic samples were studied and analyzed. Results indicate that all the samples are similar to K_0.5Na_0.5NbO₃ (KNN) in perovskite structure. With the increase of Al₂O₃ content, the X-ray diffraction peaks move to a large angle region, suggesting the substitution of niobium ions by aluminium ions and the distortion of the KNN lattice with a new phase arising. With the increase of Al₂O₃ content the grain size reduces and the dielectric constant decrease, yielding to the decrease of the electromagnetic shielding performance of ceramic. When the x is 0.4, the minimum value of reflectivity of sample is −28 dB at the frequency of 11.6 GHz. It can be concluded that both the grain size and Al₂O₃ content can obviously affect the electromagnetic properties of ceramics, which can be easily turned through a multi-layer SiO₂ heterojunction structure.