Preparation And Microwave Properties Of Double Perovskite Sr₂FeMoO₆ And Perovskite La_0.6Sr_0.4 MnO₃ Particles

Recently with the rapid development of information technology and military, stealth technology seriously electromagnetic inference pollution has triggered great interest in finding effective electromagnetic wave absorption materials with properties of wide and strong absorption frequency range, low density and high resistivity. Up to now several systems were investigated, such as nanoparticles of 3d-transition metals and improved microwave absorption properties of their core/shell structures due to the enhanced dielectric loss and the reduced eddy current loss by forming insulating shells. However, the process to obtain the core/shell structure is usually complicated. For application, it is essential to develop a material with good microwave absorption performance by a simple method.Half metallic perovskite oxides and the derivatives of A2BB'O6 double perovskite are the materials which spin polarization reaches 100%. The materials have a good application in transport and low-field magnetoresistance. This paper researches microwave absorption properties of perovskites as functional materials using the defects formed during process. For this, a series of double perovskite Sr2FeMoO6 samples which contain antisite defects and anti-phase domain were prepared by sol-gel method, and the Lao6Sr0.4MnO3 samples which exist Mn3+-Mn3+, Mn4 +-Mn4+ anti-ferromagnetic coupling of particle surface were prepared.In the study of Sr2FeMoO6 samples, the different antiphase boundary samples were prepared by changing the sintering time, the different antisite defects and grain size of samples were prepared by changing the sintering temperature. XRD patterns of samples were measured by X-ray diffraction, use the Scherrer's formula to calculate the average grain size of samples, the antisite defects of the samples were acquired by Rietevld refinement, the static magnetic properties of samples were measured by vibrating sample magnetometer (VSM) at room temperature. The dynamic magnetic properties of the mixture with sample and dielectric material are measured by vector network analysis, the reflection loss is calculated by the transmission line theory. The main conclusion shows as fellow:(1) The reflection loss was measured with the mixture of samples and the same dielectric materials. The reflection loss is related to anti-phase boundary of the sample, the reflection loss increases relevantly with the anti-phase boundary.(2) The samples was mixed with different dielectric material. The conclusion is that reflection loss is related to dielectric material, reflection loss is better when the prepared sample mixes with epoxy resin samples.(3) The dynamic magnetic properties were measured with the mixture which are made up with samples of different sinter temperature and the same dielectric material epoxy resin. And it is obtained that the reflection is the maximum when the sintering temperature is 900℃, the reflection loss reaches-49.5dB at 8.5GHz with the matching thickness of 2.15mm. When the sintering temperature is 950℃, the reflection loss is less than-1OdB in the frequency range of 5.3GHz-14.0GHz when the sample thickness is in the range of 3.0mm-1.5mm. While the reflection loss is less than-20dB in the frequency range of 5.7GHz-13.2GHz when the thickness is 3.0mm-1.5 mm. The conclusion is that double-perovskite materials have much potential in high frequency application as microwave absorber.Using the same method, nanoparticles Lao.6Sr0.4Mn03 were prepared and the good microwave absorption properties were also observed as the exist of the Mn3+-Mn3+, Mn4+-Mn4+ anti-ferromagnetic coupling.