Two-step solid-state synthesis of high-purity 413 high-entropy MAX phases based on the structural genetic mechanism and investigation of their microwave absorption performance

Abstract Difficult synthesis and low purity of 413 high-entropy MAX phase powder have severely constrained its development in the field of electromagnetic wave absorption. To address this, the present study optimized a two-step solid-phase synthesis process. By examining how different raw-material pretreatment methods affect the structural evolution of carbide precursors, we proposed a "structural genetic mechanism" that systematically explains the synthesis pathway of the 413 high-entropy MAX phase. The results show that cubic-phase carbide precursors are essential for producing high-purity 413 high-entropy MAX. Using the optimized method, we synthesized pure-phase 413 high-entropy MAX and, for the first time, successfully prepared (Mo0.2Ta0.2Nb0.2Ti0.2V0.2)4AlC3 via a conventional pressureless solid-state reaction route. Wave absorption tests indicate that the synthesized 413 high-entropy MAX phases all exhibit good absorption performance. In particular, (Mo0.2Cr0.2Nb0.2Ti0.2V0.2)4AlC3 achieved a maximum effective absorption bandwidth (EABmax) of 4.24 GHz at a thickness of 1.57 mm and a minimum reflection loss (RLmin) of -52.88 dB at 1.87 mm. (Mo0.2Ta0.2Nb0.2Ti0.2V0.2)4AlC3 showed a clear advantage at thin thicknesses, with a EABmax of 3.44 GHz at 0.93 mm and a RLmin of -51.5 dB at 0.89 mm. This study fully demonstrated the effective regulation of wave absorption performance by high-entropy engineering and provided an effective approach to expand the types of 413 high-entropy MAX phase powders, offering a useful reference for exploring this material in the field of wave absorption.