Effects of Ni²⁺, Zr⁴⁺, or Ti⁴⁺ doping on the electromagnetic and microwave absorption properties of CaMnO₃ particles

Although CaMnO₃ has been widely studied and used for its thermoelectric properties and giant magnetoresistance effect, little information exists about its application for microwave absorption. In this study, we synthesized CaMnO₃, CaNi_0.05Mn_0.95O₃ CaTi_0.05Mn_0.95O₃ and CaZr_0.05Mn_0.95O₃ with an orthorhombic system using a simple high-temperature solid-phase method. The minimum reflection loss value and effective absorption bandwidth could be efficiently improved due to the enhanced match complex permittivity produced after the Ni, Ti or Zr ions were substituted for Mn ions in CaMnO₃. The minimum reflection loss value increases to −39.7 dB from −14.1 dB and the effective absorption bandwidth increases to 4.9 GHz from 2.7 GHz. The magnetic loss results only in a negligible influence on the microwave absorption. The enhancement of microwave absorption properties was primarily due to the stronger polarization effect. When Ni²⁺, Ti⁴⁺, or Zr⁴⁺ is introduced in the CaMnO₃ lattice, the charge balance is broken, and the crystal lattice distortion increases because of the substitutive ions, interstitial ions, oxygen vacancy and exchange effect of Mn³⁺~Mn⁴⁺. The results indicate that CaMnO₃ with reasonable doping at the Mn-site could achieve excellent microwave properties of wide bandwidth, high-efficiency absorption, and adjustable response frequency.