Molten salt assisted synthesis and electromagnetic wave absorption properties of (V1−x−yTixCry)2AlC solid solutions

Abstract

MAX phase solid solutions have attracted considerable attention owing to their unique structure and properties. However, the synthesis of MAX phase solid solutions doped with multi-elements at M-sites still remains a challenge. Herein, a series of (V_1−x−yTi_xCr_y)₂AlC solid solution powders are prepared through the reactions of V, Ti, Cr, and Al metals and graphite in molten NaCl/KCl salts, and their electromagnetic (EM) wave absorption properties are systematically investigated. In comparison with Ti₂AlC, V₂AlC and Cr₂AlC, (V_1−x−yTi_xCr_y)₂AlC solid solutions exhibit prominent EM absorption performance. Specifically, the minimum reflection loss (R_L) value of (V_0.6Ti_0.2Cr_0.2)₂AlC is −56.2 dB at 12.07 GHz with a sample thickness of 1.75 mm, and the optimized effective absorption bandwidth (E_AB, R_L < −10 dB) covers the whole X band with 4.16 GHz at 2.00 mm. Furthermore, the strong dielectric resonance is presented in the range of 7–13 GHz for all (V_1−x−yTi_xCr_y)₂AlC, indicating that both dipole polarization and conduction loss contribute to the excellent dielectric loss of doped MAX phases. Theoretical analysis demonstrates that the polarization loss is attributed to the anisotropic conductivity of MAX phases and M-site doping, which further weakens the electric conductivity. As a result, plenty of dipoles are involved and polarization relaxation occurred when the (V_1−x−yTi_xCr_y)₂AlC solutions are radiated by EM. Considering the numerous kinds of MAX phase solid solutions, this work paves the way to study the EM absorption performance of high-entropy or other MAX phase solid solutions.