Exploration of the microwave absorption mechanism of rare earth enhanced M-type strontium ferrite: synergistic effect of lattice occupation and impurity phase

How do rare earth (RE) ions affect the microwave absorption performance of M-type hexagonal ferrites? We synthesized Sr_0.9RE_0.1Fe₁₂O₁₉ and SrFe_12−xRE_xO₁₉ (x = 0.05, 0.1, 0.4, 0.8, 1.6, RE = La ~ Gd) series to investigate the similarities and differences in the mechanism of RE ion substitution on the absorption properties of materials. The occupancy tendency and substitution limit of RE ions in the M phase lattice, as well as the formation of impurity phases at grain boundaries, are key factors affecting the microwave absorption performance of materials. The synthesized materials include both pure M phase and coexistence of M phase and heterophases, and the heterophases are mainly FeRE_ySr_1−yO_3−z, CeO₂ and RE₃Fe₅O₁₂. The strontium ferrite substituted with La and Ce has better absorption effect in pure M phase. The RL_min of SrFe_11.9La_0.1O₁₉ can reach − 60.61 dB and the EAB_max is 6.24 GHz with a thickness of 1.96 mm. Strontium ferrite substituted with Pr and Nd can achieve good absorption effects over a large range of substitution amounts, which is not only related to their high substitution limit in the M phase, but also to the perovskite type impurities generated by excessive substitution. The RL_min of the SrFe_10.4Nd_1.6O₁₉ can reach − 75.34 dB, and the EAB_max is 5.16 GHz with a thickness of 1.9 mm. The distribution of strontium ions in the two phases also becomes a key factor affecting the absorption performance. The substitution limit of Eu and Gd in the M phase is small, and excessive addition can form high resistance impurities, resulting in poor absorption efficiency of the system.