Defect Dipole-Induced HfO₂‑Coated Ti₃C₂T_x MXene/Nickel Ferrite Nanocomposites for Enhanced Microwave Absorption

This work reports for the first time the synthesis of a HfO₂-coated Ti₃C₂T_x MXene sandwich-like nanostructure (MXHf) using a simple hydrothermal method and their excellent microwave absorption property in combination with nickel ferrite and epoxy matrix. The nanocomposites of 2, 3, and 4 mm thick samples were tested for microwave absorption in the X-band, and a minimum reflection loss (RL_min) of −20.9 dB with EAB (effective absorption bandwidth) of 2.32 GHz was achieved for the 3 mm thick sample. Its superior performance results from the strong dielectric polarization of defect dipole in the MXene structure, the high number of oxygen vacancies brought about by HfO₂ nanoparticles, rich micro-interfaces in the sandwich-like HfO₂-Ti₃C₂T_x-HfO₂ structure, and impedance matching by NiFe₂O₄. A probable mechanism of absorption is proposed. Hence, HfO₂/Ti₃C₂T_x/NiFe₂O₄ nanocomposites possess essential properties for real-time application in the defense and telecommunication industries.