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 0.9 RE 0.1 Fe 12 O 19 and SrFe 12− x RE x O 19 ( 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 y Sr 1− y O 3− z , CeO 2 and RE 3 Fe 5 O 12 . The strontium ferrite substituted with La and Ce has better absorption effect in pure M phase. The RL min of SrFe 11.9 La 0.1 O 19 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 10.4 Nd 1.6 O 19 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.