| AB2Si2O7island silicates with low dielectric constant have been used in important fields such as 5G communication,Internet of Things,and remote sensing.In this work,BaCu2Si2O7ceramics,which are AB2Si2O7island silicates,were firstly investigated systematically for their synthesis conditions,crystal structure,chemical bonding vibration information and dielectric properties.Subsequently,BaCu2-xMnxSi2O7（0≤x≤0.04）and Ba1-ySryCu2Si2O7（0≤y≤0.08）ceramics were constructed by using Mn ions and Sr ions to substitute the B/A site,respectively.The effect of ion doping on the dielectric properties was discussed by analyzing the phase composition,microstructure and sintering characteristics.And the intrinsic correlation between crystal structure and dielectric properties is constructed based on the chemical bonding theory（P-V-L theory）.The details and conclusions of this work are as follows:（1）A series of BaCu2Si2O7ceramics were prepared by solid-phase reaction method and the dielectric properties sintered at different conditions were investigated.When the calcination temperature was 1000℃,the raw materials completely reacted to form BaCu2Si2O7phase with orthogonal structure.With the sintering temperature in range of 1030～1070℃,the relative density first increased and then decreased.Besides,the dielectric constant and quality factor also showed a trend of increasing and then decreasing with the increase of sintering temperature.The best dielectric properties of BaCu2Si2O7ceramics were obtained when the calcination temperature was 1000℃and the sintering temperature was 1050℃,and the dielectric constantεrwas 7.85,the quality factor Qfwas 48660 GHz,and the temperature coefficientτfwas-26.3 ppm/℃.（2）In order to further improve the dielectric properties of BaCu2Si2O7system,Mn ions with similar radius to Cu ions in B-site were selected for substitution and BaCu2-xMnxSi2O7（0≤x≤0.04）ceramics were synthesized in the sintering temperature range of 1000～1040℃.In all samples,Mn ions successfully entered the lattice and occupied the position of Cu ions to form BaCu2Si2O7solid solution.The dielectric constant became larger and then smaller with the increase of the introduced content of Mn ions,which was attributed to the combined effect of porosity and ion polarization rate.The changes in lattice energy and relative density lead to a trend of increasing and then decreasing appeared in quality factor.The temperature coefficient decreased with the increase of x under the effect of gradually decreasing Cu/Mn-O bonding energy.Besides,Raman shifts that resulted from stretching vibration of Cu-O bond exhibited an opposite trend compared withεr.FWHM of Raman peak for Si-O bond varied inversely with the Qfof BaCu2-xMnxSi2O7ceramics.When the Mn ion doping content was 0.02 mol and the sintering temperature was 1020℃,the BaCu1.98Mn0.02Si2O7ceramic had the best dielectric properties with dielectric constantεrof 8.12,quality factor Qfof 54692 GHz,and temperature coefficientτfof-29.5ppm/℃.（3）Ba1-ySryCu2Si2O7（0≤y≤0.08）ceramics were prepared using the solid-phase method at 990～1030℃ sintering temperature by using Sr ions to replace the A-site Baions in BaCu2Si2O7ceramics.In the range of 0≤y≤0.08,the XRD patterns of Ba1-ySryCu2Si2O7（0≤y≤0.08）ceramics were all matched to the BaCu2Si2O7phase.The dielectric constant became smaller gradually under the effect of the smaller ion polarization rate of Sr ions.The quality factor exhibited a trend of increasing and then decreasing by the combined effect of lattice energy and relative density.The decrease bond energy of Ba/Sr-O bond caused the decreasing of temperature coefficient.The best dielectric properties of Ba0.96Sr0.04Cu2Si2O7ceramics withεrdielectric constant of 7.65,quality factor Qfof 55986 GHz and temperature coefficientτfof-28.9ppm/℃ were obtained when the doping content of Sr ions was 0.04 mol and the sintering temperature was 1010℃. |
