Electromagnetic wave absorption and dielectric-modulation of metallic perovskite lanthanum nickel oxide

Electromagnetic (EM) wave absorption properties of metallic perovskite lanthanum nickel oxide (LNO) powder and dielectric-modulated LNO-FeCo/C composites were investigated. Reflection loss (RL) of the LNO-paraffin composites depends on the mass ratio of LNO powder dispersion in the paraffin matrix, in which the optimal RL of -24.7 dB at 17.6 GHz with the absorbent layer thickness of 1.6 mm is obtained at the 10 wt% LNO-paraffin composite, just below the percolation threshold (PC) of the LNO dispersion in the paraffin matrix. Three absorption peaks in the frequency dependence of RL of the 10 wt% LNO-paraffin composite are ascribed to the dielectric relaxations which occurred at frequencies of about 3.3, 9.2 and 15.1 GHz. Dielectric-modulation by metal-conductive LNO powder significantly increases the relative complex permittivity of the (x) LNO-(y) FeCo/C-paraffin composites and a good impedance match coming from the dielectric-modulation by the LNO powder would be obtained just below the PC of the LNO powder dispersion in the paraffin matrix. The (8 wt%) LNO-(32 wt%) FeCo/C-paraffin composite exhibited an enhanced EM wave absorption performance, in which RL values less than -20 dB can be obtained in the 2-18 GHz range by choosing an appropriate thickness from 1.3 mm to 8 mm and the minimum RL is 50.6 dB at 9 GHz with the absorbent layer thickness of 2.4 mm.