Enhanced microwave absorption in Fe/K Co-doped LaNiO₃–Al₂O₃ composites via defect engineering and dielectric polarization

The development of high-performance microwave absorbing materials is critical to enhancing military invisibility and to ensuring the security of the electromagnetic environment in the 5G era. The study synthesized the lanthanum nickelate perovskite ceramic by high temperature solid-state reaction, including undoped LaNiO₃ (LNO), Fe-doped LaNi_0.7Fe_0.3O₃ (LNFO), K-doped La_0.8K_0.2NiO₃ (LKNO) and Fe/K co-doped La_0.8K_0.2Ni_0.7Fe_0.3O₃ (LKNFO), and composited with Al₂O₃ to achieve impedance matching. XRD and refinement indicated lattice expansion and oxygen vacancy formation via Fe/K doping. SEM revealed that the synthesized material exhibited regular cubic particles, and with K₂CO₃ decomposition at high temperatures resulting in grain refinement. XPS and conductivity measurements confirmed that Fe3+ stabilized Ni3+ valence states and K+ introduced additional holes, thereby enhancing carrier density and dielectric polarization. Electromagnetic characterization indicated that dielectric loss dominated the absorption, with A4 (Fe/K co-doped) exhibiting multiple relaxation processes, superior dielectric loss tangent, and enhanced impedance matching. As a result, A4 achieved a broad effective absorption bandwidth of 3.01 GHz (8.36–11.37 GHz) at 1.6 mm thickness. CST simulations further verified that A4 possessed the lowest radar cross-section (−43.28 dBm2), consistent with experimental reflection loss results. This work demonstrates that Fe/K co-doping combined with Al₂O₃ compositing provides an efficient strategy to balance impedance matching and attenuation capability, offering new insights into the design of lightweight, broadband, and high-performance microwave absorbing materials.