Study On The Structure And Properties Of Barium Strontium Titanate Modified By Spinel Structure Microwave Dielectric Materials

Barium strontium titanate(Ba_1-xSr_xTi O₃,BST)is preferred for tunable high frequency devices due to its strong nonlinear dielectric properties.However,due to the high dielectric permittivity,it is difficult to meet the requirements of impedance matching and high power.Ferroelectric-dielectric composite is considered as an effective method to modify BST-based ceramic materials.However,the reduction of dielectric permittivity usually worsens the tunability or Q value.In this work,Ba_1-xSr_xTi O₃ microwave dielectric ceramic composite with spinel structure was used to break the limitation of this contradiction on dielectric properties,and BST matrix composite ceramic material with excellent dielectric properties was developed.The main research contents and conclusions are as follows:BST ceramics were modified by Zn Mn₂O₄ and Co Al₂O₄ microwavable spinel dielectric ceramics.The relationship between ion diffusion,defect structure,recombination effect and dielectric properties was studied.The res ults show that the Curie peak of the material is inhibited and widened with the increase of microwave medium addition,and the phase transition dispersion phenomenon occurs and the relaxation and dispersion degree are enhanced.The gradual decrease of dielectric permittivity and the increase of Q value are attributed to the recombination effect of the two phases.Tunability remains stable at higher ranges due to a combination of Curie temperature variation and connectivity.By infrared and Raman spectroscopy,it is found that lattice vibration is the intrinsic cause of tunability,dielectric permittivity and Q value of composite ceramics.The dielectric permittivity of（1-x）Ba_0.6Sr_0.4Ti O₃-x Zn Mn₂O₄ composites decreases from 5423 to 595 when the composite amount of Zn Mn₂O₄ increases from 0 wt.%to 40 wt.%,and the serialized control of dielectric permittivity of（1-x）Ba_0.6sr_0.4Ti O₃-x Zn Mn₂O₄ ceramics is realized.The dielectric adjustable rate is kept above 26.5%@30k V/cm.When x=40 wt.%,microwave dielectric properties is good:?’=595,Q=381@1501 MHz and T=26.8%@30 k V/cm.BST ceramics were modified by spinel microwave dielectric Co₂Ti O₄ and Mg Ga₂O₄.When x=10 wt.%,the agglomeration effect of microwave dielectric material limited the grain growth of BST,thus reducing the sintering density and Q value.According to the fitting result of Curie-Weiss law,the ion diffusion concentration reaches saturation.With the further increase of x value,due to the recombination effect,the relative dielectric permittivity gradually decreases and the Q value gradually increases.The effect of microwave dielectric composite modification on the tunability of BST is reduced,and the tunability is kept relatively high.The optical dielectric properties before and after ion substitution are calculated.The results show that the real part of the optical dielectric permittivity is effectively reduced and the imaginary part is increased after ion substitution.The finite element simulation verifies that the connectivity of ceramic phase has a decisive effect on the dielectric properties of ferroelectric-dielectric composites.With the decrease of BST connectivity,the dielectric properties of composite ceramics are effectively reduced.When the Mg Ga ₂O₄recombination is 50 wt.%,the relative dielectric permittivity of the ceramic is208（at resonant frequency）,the Q value is 632（3.312 GHz）,and the tunability is10.6%（30 k V/cm,room temperature and 10 k Hz）,which may be an ideal candidate for tunable component applications.