Preparation Of (Fe,Co,Ni,M,Zn)O_x(M=Cu,V) High Entropy Ceramics And Its High Temperature Absorbing Mechanism

Stealth technology is currently a hot topic of research in the military.The purpose of“stealth”is usually achieved by using electromagnetic wave-absorbing materials to reduce radar scattering cross-section.The electromagnetic wave-absorbing materials consume electromagnetic waves by absorbing incident electromagnetic wave energy and converting it into thermal energy.With the development of supersonic cruise missiles and high-Mach fighters,there is a growing need for absorbent materials adapted to high-temperature environments.Given the performance failure of traditional wave-absorbing materials at high temperatures,there is an urgent need for the industry to find new wave-absorbing materials.High entropy oxide ceramics have received a lot of attention from the industry because of their good high-temperature stability,simple preparation process and tunable properties.In this work,the biphase structure and elements of high entropy oxide ceramics are designed to achieve effective modulation of high-temperature electromagnetic wave absorption properties,and the mechanism related to the loss of electromagnetic waves by its biphasic dielectric structure and the magnetic system is elucidated.The main research contents are as follows:Two types of biphasic high entropy oxide ceramics,magnetic（Fe,Co,Ni,Cu,Zn）O_xand dielectric（Fe,Co,Ni,V,Zn）O_x were designed.First,（Fe,Co,Ni,Cu,Zn）O_x high-entropy ceramics were prepared by solid-phase reaction method in the temperature range of 1000-1300°C using equimolar ratios of raw materials;To improve the material homogeneity and sintering temperature,（Fe,Co,Ni,V,Zn）O_x high-entropy ceramics were prepared by replacing Cu O with V₂O₅,still using the equimolar ratio of raw materials,in the temperature interval of 850-1000°C.Experimental results:The（Fe,Co,Ni,Cu,Zn）O_x high entropy oxide ceramics have both spinel and rock salt phase structures.At room temperature,the sample sintered at1200°C has good absorbing performance,with a minimum reflection loss of-52.3 d B and an effective absorbing bandwidth of 3.0 GHz.The absorbing performance is mainly dominated by magnetic loss and supplemented by dielectric loss,and the two consume electromagnetic waves together.At 473 K,the minimum reflection loss of the sample sintered at 1200°C is-34.6 d B,and the effective bandwidth is 1.9 GHz.The electromagnetic wave is mainly consumed by dielectric loss.In addition,（Fe,Co,Ni,V,Zn）O_x oxide ceramics have the vanadate phase and spinel phase structure,and the sintering temperature is lower than（Fe,Co,Ni,Cu,Zn）O_x.At room temperature,the minimum reflection loss of the sample sintered at 900°C is-36.5 d B,and the effective absorption bandwidth is 2.8 GHz.The electromagnetic wave is consumed mainly by dielectric loss.At 473 K,the sample sintered at 900°C has a minimum reflection loss of-45.5 d B and an effective absorption bandwidth of 0.6 GHz.Dielectric loss is the main one.The experimental results show that（Fe,Co,Ni,Cu,Zn）O_x high-entropy oxide ceramics containing spinel and rock salt phases have excellent wave absorption performance at room temperature,mainly from the magnetic loss due to their magnetic structure,while the increased in temperature decreases their absorption efficiency.The（Fe,Co,Ni,V,Zn）O_x high-entropy oxide ceramics containing vanadate and spinel phases have good wave absorption properties at room temperature,and the electromagnetic wave absorption efficiency is positively correlated with temperature,which mainly stems from the positive temperature dependence of the dielectric properties of the materials.Therefore,the design of dielectric loss capability of dual-phase high-entropy oxide ceramics is an effective way to achieve high-temperature microwave absorption.