Study On Lattice Dynamics For Microwave Dielectric Ceramics Of Scheelite And Olivine Structure

In recent years,with the rapid development of microwave communication technology,people's requirements for electronic components are gradually increasing,which puts higher demands on the performance of microwave dielectric ceramics.Microwave technology turns to higher frequencies,that is,the direction of millimeter wave or submillimeter wave.In this work,Ca1+xWO4(-0.04 ? x ?0.04)ceramics,LiNiPO4 and LiMg1-xNixPO4 ceramics formed by Ni2+ions doping were prepared by solid-state reaction method.The effects of small changes in ceramic composition on dielectric properties,sintering process and the effect of element doping on dielectric properties were investigated.X-ray diffraction(XRD),scanning electron microscopy(SEM)and Raman spectroscopy(Raman)and Fourier Far-infrared spectroscopy(FTIR)techniques were used in this paper.The relationship between the structures and properties of ceramics were explored and analyzed deeply.(1)A non-stoichiometric Ca1+xWO4(-0.04 ?x?0.04)ceramic sample was prepared by a conventional solid phase reaction method.The results show that all samples form a single scheelite structure without the second phase.The relationship between the intrinsic dielectric properties and the Raman mode was analyzed in detail.It is found that the half-width value of the Bg(Ca)mode is positively correlated with the dielectric loss value(calculation of the damping formula)and the Raman shift of the v4(Bg)mode.There is a negative correlation between the intrinsic dielectric constants calculated by the C-M formula.The contribution of each mode to dielectric properties was investigated and it was observed that the external mode plays an important role in the dielectric properties of ceramics.At x=-0.01,the as-sintered Ca0.99WO4 ceramic at 1150? has excellent dielectric properties:1.Calculated by C-M and damping equation:?r=10.62,tan??4.62×1 0-4,calculated based on four-parameter model(FPSQ):?r=10.19,tan??2.35×10-4.(2)LiNiPO4 ceramics were prepared from conventional solid phase reaction methods at different temperatures(775-850?).The X-ray pattern confirmed that LiNiPO4 ceramics of single-phase olivine(Pnma,No.62)were formed in all samples above 750?.A dense structure was obtained at 825?,with a high relative density of 95.09%,excellent dielectric properties of ultra-low ?r of 5.18,and Q×f of 24,076 GHz.The real and imaginary parts of ?(?)and the imaginary part of ?-1 are obtained by four-parameter fitting,which proves the reliability of the results after applying FPSQ.The intrinsic dielectric properties of the samples calculated using far infrared reflectance spectra are very consistent with the measured results.(3)After Ni2+doped LiMgPO4 ceramics,solid solution can be formed,and the LiNiPO4 phase gradually increases with the increase of doping amount.It can be seen from the SEM that the ceramic has a good microscopic shape at x=0.1.As the doping amount increases,the dielectric constant and Q×f of the ceramic decrease first and then increase.When x?0.1,the optimal value?r=5.2,Q×f?24076 GHz,?f=-36.5 ppm/?.This is because at x=0.1,the relative density of ceramic materials is higher than others,and the relative density is closely related to the performance of ceramics.