Evaluation and Failure Mechanism of High‐Temperature Microwave Absorption for Heterogeneous Phase Enhanced High‐Entropy Transition Metal Oxides

Abstract Herein, magnetic and conductive heterogeneous nickel‐matrix alloy is in situ constructed in the high‐entropy transition metal oxide matrix using a reductive circumstance, to form the high‐temperature resistant microwave absorbers. The ohmic, dielectric polarization and magnetic loss are enhanced synergistically, prompting the improvement of loss capacity and optimization of the impedance matching feature. The composites achieve over 90% absorption in the whole Ku band with a thickness of just 1.55 mm at room temperature. Moreover, the in situ high temperature measured microwave absorption keeps stable till 500 °C. In situ characterizations are employed to investigate the evolution processes and failure mechanisms. As the temperature elevates, there are three distinct stages. The absorber goes through minor chemical reactions, consequent elimination of magnetic loss, and a rapid increase in electroconductivity. These behaviors culminate in impedance mismatch, finally worsening its absorption performance at elevated temperatures. The proposed evaluation process reveals how the above irreversible and reversible behaviors affect high‐temperature microwave absorption, providing an effective theoretical basis for the design of high‐temperature microwave absorbers.