High-entropy enhanced microwave absorption in MAX phases

The application of microwave absorption materials, which can effectively convert electromagnetic energy into thermal energy and/or other forms of energy, can effectively solve the increasingly serious electromagnetic pollution. As a type of promising microwave absorption material, ternary transition metal carbides/nitrides MAX phases possess layered structure and superior conduction loss capability. However, poor impedance matching and single polarization loss type seriously hinder their improvement of microwave absorption performance. High-entropy engineering is expected to be an effective strategy to address the above problems simultaneously. Herein, a series of low-, medium-, and high-entropy MAX phases with Ti2AlC structure were successfully synthesized and their structure, composition, and morphology were comprehensively characterized. High-entropy MAX phase (Ti1/5Zr1/5V1/5Nb1/5Ta1/5)2AlC presents excellent microwave absorption performance with the optimal minimum reflection loss (RLmin) of −47 dB at 11.92 GHz (a thickness of 2.4 mm) and optimal effective absorption bandwidth of 3.92 GHz between 8.48 and 12.4 GHz (a thickness of 2.78 mm), which are better than those of our prepared low-/medium-entropy MAX phases as well as most of the other previously reported MAX phases. Such excellent microwave absorption performance of (Ti1/5Zr1/5V1/5Nb1/5Ta1/5)2AlC is attributed to high-entropy engineering, which not only optimizes the impedance matching through regulating permittivity but also introduces more polarization loss type and amount. This work reveals that high-entropy engineering is not only a workable method to enhance the microwave absorption performance in MAX phases, but also an effective strategy to tailor the balance between impedance matching and loss capability through compositional design in single-phase systems.