Effects of Temperature-Induced Lattice Distortion and Phase Evolution on Electromagnetic wave absorption in High-Entropy Powders

Abstract

High entropy transition metal diborides (HEB) have garnered significant attentions in various fields due to their excellent thermal stability, oxidation resistance, and electromagnetic wave absorption (EMA) properties. Nevertheless, the mechanism underlying their EMA enhancement remains incompletely understood. In this study, (Ti, Zr, Hf, Nb, Ta)B2 powder, a baseline material for HEB, was synthesized through a sol-gel method using inorganic salts as metal sources. By systematically varying the synthesis temperature (1400℃, 1650℃, and 1800℃, designated as MB14, MB16, and MB18, respectively), HEB powders with varied degrees of solid solution were successfully prepared. Compared to ZrB2, the impedance matching and reflection loss (RL) of MB14 had slightly improved due to the element solid solution and the presence of the byproduct hexagonal BN which encapsulated diboride powders. MB18 achieved the minimum RL value of -34.79 dB at 17.84 GHz and 3.8 mm, and an effective absorption bandwidth (EAB) 1.12 GHz. As the synthesis temperature increased, the lattice distortion caused by multi-principal elements became more pronounced, which not only regulated impedance matching by reducing the dielectric constant but also induced various dielectric loss mechanisms. Therefore, for HEB, processing parameters should be optimized to suppress phase separation, thereby enhancing their EMA performance.