Preparation And Microwave Absorption Properties Of PrMnO₃ System

With the advances in electronic technology,microwave radiation pollution is increasingly attracting concerns.In order to solve microwave pollution,the research and development of electromagnetic wave absorbing materials has caused special attention to scholars.This paper prepares REMnO₃（RE=La,Pr,Nd）,three kinds of rare earth manganese oxides by sol-gel method,via a series of characterization and performance testing,and it is determined that PrMnO₃ is an experimental base.The experimental factors affecting the absorbing performance of PrMnO₃,such as calcination temperature and the mass ratio of composite with paraffin wax during pressing test sample,were investigated.Subsequently,the influence of substitution of Pr³⁺with different contents of Sr²⁺,Ba²⁺,La³⁺on the structure,morphology,magnetic properties and microwave absorption properties of PrMnO₃ was explored.Firstly,LaMnO₃,PrMnO₃ and Nd MnO₃ single-phase rare earth manganese oxides were prepared by sol-gel method.XRD,SEM,XPS,BET,VSM,VNA and other equipment were used to characterize the structure and performance of the samples.The morphology of the three rare earth manganese oxides powders is similar and the powders are spherical or ellipsoid.At a thickness of 3.2 mm,PrMnO₃ has the minimum reflection loss reaching(RL_min)-35.72 dB（absorption rate of 99.97%）,and the corresponding effective absorption bandwidth（RL<10 dB）is 5.04 GHz.The influence of mass ratio of PrMnO₃ and paraffin composite on the absorbing performance of the tested sample was researched.The results showed that the sample with mass fraction of 40 wt%achieved the minimum reflection loss value of-30.04 dB at the thickness of d=3.3 mm,and had the best absorbing performance.The particle size of the PrMnO₃compound became bigger with the improvement of the calcination temperature,and the values ofε’andε’’gradually decrease with the improvement of temperature and frequency.When the particle size is d=3.4 mm and the calcination temperature is 800℃,PrMnO₃ has the best wave absorption performance,up to-38.18 dB,and the corresponding frequency is 10.00 GHz,belonging to the X-band.The magnetic curves of Pr_1-xSr_xMnO₃ and Pr_1-xBa_xMnO₃ do not reach saturation at room temperature under the field strength of 2 T,and they are nearly straight,and have low coercivity.When the doping amount of Sr²⁺is x=0.05,the effective bandwidth of the sample Pr_0.95Sr_0.05MnO₃ is increased to 6.96 GHz.When the doping amount is increased to x=0.1,the minimum RL is-50.21 dB,the corresponding matching frequency is obtained at12.08 GHz,and the corresponding absorption layer thickness is only 2.5 mm.Pr_0.9Sr_0.1MnO₃ powder shows excellent microwave absorption capacity even at a lower thickness.When d=5.5 mm,Pr_0.94Ba_0.06MnO₃ achieved the minimum reflection loss of-18.97 dB at 5.04 GHz（C-band）.This indicates that Pr_0.94Ba_0.06MnO₃ also has good microwave absorption ability in low frequency C-band.The X-ray diffraction peak of Pr_1-xLa_xMnO₃ moved to Smaller angle with the improvement of La³⁺doping amount.Pr_0.9La_0.1MnO₃ reached the absorption strength of-53.96 dB at 9.84 GHz,while the corresponding material thickness was 3.4 mm.In terms of broadband effect,the maximum bandwidth of 4.8 GHz is obtained when the doping amount is x=0.1.This indicates that the absorbing material Pr_0.9La_0.1MnO₃ not only has good absorption performance,but also has excellent broadband effect.