Study On Lattice Dynamics Of A(Mg_0.5B_0.5)O₃ Microwave Dielectric Ceramics

In recent years,communication technology has developed rapidly,and the performance requirements of electronic components have become higher and higher.This has also set higher requirements for the performance of microwave dielectric ceramics,microwave technology is developing towards higher frequency,i.e.mllimeter wave or submillimeter wave.In this thesis,the solid-phase reaction method was used to prepare the Nd(1+x)(Mg1/2Sn1/2)O3(-0.04≤x≤0.04)ceramics,Sr(Mg1/2W1/2)O3 ceramics and A(Mg1/2W1/2)O3(A=Ca,Ba,Sr)ceramics formed by the change of A-site atom.The effects of minor composition changes of ceramics,sintering process and element changes on dielectric properties were explored.In this paper,X-ray diffraction(XRD),scanning electron microscopy(SEM),Raman spectroscopy(Raman),and Fourier far-infrared spectroscopy(FTIR)techniques are used to deeply analyze and explore the relationships between the structures and properties of ceramics.(1)Non-stoichiometric Nd(1+x)(Mg1/2Sn1/2)O3(-0.04≤x≤0.04)ceramic samples were prepared by conventional solid-state reaction methods.The results showed that all samples formed monoclinic perovskite structure with space group P21/n(JCPDS#16-1439).The relationship between the crystal structure and the dielectric properties is analyzed in detail using the Raman model as the medium.The dielectric constant has a negative correlation with the Raman shift of the F2g(A)mode,the average bond length has a positive correlation with the dielectric constant,and the dielectric loss has a positive correlation with the Raman shift and FWHM value of the Aig(O)mode.The contribution of each mode to the dielectric properties is also investigated,and it is observed that the external mode has the greatest influence on the dielectric properties of ceramics.After performance testing and analysis,the best performance can be obtained for ceramic samples of Nd(1+x)(Mg1/2Sn1/2)O3(-0.04 ≤x≤0.04)when x=0.01,and the dielectric properties obtained through C-M and damping equations(εr=19.94,tanδ=3.18×10-4)are basically consistent with the calculated values of the four-parameter semi-quantum(FPSQ)model(εr=20.41,tanδ=2.98 × 10-4).(2)Sr(Mg1/2W1/2)O3 ceramics were prepared at different sintering temperatures(1450-1525℃)using conventional solid-phase reaction methods.The X-ray diffraction patterns showed that when the sintering temperature exceeded 1450℃,all samples formed Sr(Mg1/2W1/2)O3 ceramics with face-centered cubic composite perovskite structure(Fm-3m).The ceramics obtained the dense structure at 1475℃ with a high relative density of 95.09%,and excellent dielectric properties(εr=15.18,Q×f=24076 GHz,f=11.04GHz).The FPSQ model was used to calculate the intrinsic properties of the samples,and the results were in good agreement with the measured values.(3)Sr(Mg1/2W1/2)O3,Ba(Mg1/2W1/2)O3,Ca(Mg1/2W1/2)O3 ceramics were prepared by solid-state reaction method at 1475℃.Using X-ray diffraction,infrared and Raman spectroscopy to study the relationships between the crystal structures and dielectric properties of the A(Mg1/2W1/2)O3(A=Ba,Sr,Ca)microwave dielectric ceramics system.