Enhanced dielectric and microwave absorption properties of CaMnO₃ powders by Sr doping in the 8.2–18 GHz band

Ca_1-xSr_xMnO₃ (x = 0; 3%; 5%; 10%) powders were synthesized via a solid-state reaction for microwave absorption applications in the frequency range of 8.2–18 GHz (X and Ku band). The results suggested that the crystal structure of the samples belonged to the orthorhombic system without other phases presented. Sr²⁺ ions were inserted into the crystal lattice of CaMnO₃. The minimum reflection loss (RL) value of a pure CaMnO₃ sample reached −16.3 dB at 11.7 GHz and the effective absorption bandwidth was 2.9 GHz (10.5–13.4 GHz) with a thickness of 2.2 mm. The complex permittivity of the CaMnO₃ was greatly increased by Sr-doping. Because of better impedance matching and higher dielectric loss, the microwave absorption properties of doped samples were effectively enhanced. The optimum microwave absorption properties were obtained when the dopant concentration was 10%. For Ca_0·9Sr_0·1MnO₃, the minimum reflection loss reached −46.1 dB at 17.4 GHz with a thickness of 1.4 mm, and the effective bandwidth was 4.7 GHz which covered from 13.0 GHz to 14.7 GHz with a matching thickness of 1.6 mm. This study demonstrated that CaMnO₃ can be used as a potential microwave absorbing material and its absorbing performance can be effectively tuned by doping Sr²⁺ ions.