Study On The Intrinsic Properties And Structure-Property Relationships Of Borate Microwave Dielectric Ceramics With Low Dielectric Constant For 5G Communication

With the development of science and technology,wireless communication has made tremendous progress.A shortage of traditional frequencies has,however,resulted in an expansion of the available frequency range to millimeter waves.Microwave dielectric ceramics with a low dielectric constant to effectively reduce signal delay are required for use in UHF millimeter wave and substrate applications.The present research systematically investigates the Sr Sn（BO₃）₂ ceramics,the Sr Sn（BO₃）₂–x wt.%Li F（x=0.5～3）ceramics and the（1-x）Sr Sn（BO₃）₂-x Ti O₂ ceramics with low dielectric constant.The crystal structure parameters were obtained through the XRD refinement.The vibration modes were obtained by referring to the group theory analysis results,and the Raman and FTIR spectra were identified.By combining the above theoretical analysis with microscopic morphology and bulk density,the intrinsic characteristics that influence the dielectric properties of microwave dielectric ceramics are discussed in depth.The relationship between the intrinsic properties of microwave dielectric ceramics obtained by FTIR spectra and the theoretical calculation values and the measured values are also studied.From the perspective of lattice dynamics,Raman and FTIR spectroscopy were used to investigate the crystal structures,dielectric properties and lattice vibration characteristics of microwave dielectric ceramics,and the structure-property relationship was established.The following are the main findings of the above research:（1）Sr Sn（BO₃）₂ ceramics were successfully prepared by the traditional solid-state sintering method at different sintering temperatures.As a results of an XRD analysis and a comparison with the ICSD#74-2213 card,no other impurity peaks were identified,indicating the formation of pure Sr Sn（BO₃）₂ ceramics.The Raman scattering spectrum shows seven Raman active vibration modes,located at 183 cm^-1,236 cm^-1,381 cm^-1,428 cm^-1,639 cm^-1,748 cm^-1,1216 cm^-1 respectively.As a result of fitting the infrared reflection spectrum with the FPSQ model,the calculated intrinsic dielectric properties and theoretical values do not differ significantly from those measured values,indicating that the dielectric properties of Sr Sn（BO₃）₂ ceramics in the microwave frequency band are primarily a result of internal ion displacement polarization.Using a Raman scattering spectra,a relationship is established between the structure and performance of Sr Sn（BO₃）₂ ceramics.When the A_g mode moves to a higher wave number,the B-O bond length decreases,causing the polarizability to decrease,which in turn decreases the dielectric constant.The FWHM value of v₂ mode is related to the order degree of crystal structure,and the order degree is positively correlated with the value of Q×f.Upon sintering at 1150°C,Sr Sn（BO₃）₂ ceramics exhibit excellent microwave dielectric properties（ε_r=5.42,Q×f=32,618 GHz,f=15.68 GHz,τ_f=-48.28 ppm/°C）.（2）Sr Sn（BO₃）₂–x wt.%Li F ceramics with 950°C sintering temperature were successfully prepared by traditional solid-state sintering method.By analyzing XRD and SEM,it was concluded that there was no second phase including Li F was found detected,and that Li F existed in an amorphous state,and that they did not react together.Each vibration mode parameter and its respective dielectric response contribution obtained by fitting infrared reflection spectrum with FPSQ model（ε_j,tan（δ_j）/ω）,Among them,mode 1 and mode 2 have the greatest impact on the dielectric properties,and mode 2 has the largest contribution to the dielectric constantΔε_j=44.25%,the maximum contribution of mode 2 to dielectric loss isΔtan（δ_j）/ω=53.84%.Using Raman scattering spectroscopy,the relationship between the structure and properties of Sr Sn（BO₃）₂–x wt.%Li F ceramics was constructed by.With the increase of Li F content,when the A_g mode moves to a higher wave number,the decrease of the B-O bond length leads to the decrease of the polarizability,so the dielectric constant decreases.The FWHM value of v₂ mode is related to the order degree of crystal structure,and the order degree is positive correlated with the value of Q×f.The microwave dielectric properties of Sr Sn（BO₃）₂–3 wt.%Li F ceramics are exceptional（ε_r=5.17,Q×f=42,211 GHz,τ_f=-42.31 ppm/°C）.（3）Using the traditional solid state sintering method,（1-x）Sr Sn（BO₃）₂-x Ti O₂ceramics with sintering temperature of 1150°C have been successfully prepared.According to XRD analysis,the（004）diffraction peak of the added phase Ti O₂ was detected,indicating that a multiphase ceramic was formed from the Ti O₂ phase and Sr Sn（BO₃）₂ phase.SEM analysis reveals that with the increase of Ti O₂ addition,the pore of the sample grew and the grain boundary becomes blurred.According to the Raman scattering spectrum,there is a Raman peak around 348 cm^-1,and its intensity increases over time.The vibration mode of Ti O₂ is represented by this.Meanwhile,the v₁ vibration mode gradually increases as Ti O₂ content increases.Each vibration mode parameter and its respective dielectric response contribution obtained by fitting infrared reflection spectrum with FPSQ model（ε_j,tan（δ_j）/ω）,the contribution of mode1 to the dielectric constant is the largestΔε_j=23.31%,the maximum contribution of mode 2 to dielectric loss isΔtan（δ_j）/ω=45.75%.Through Raman scattering spectroscopy,the relationship between the structure and properties of（1-x）Sr Sn（BO₃）₂-x Ti O₂ ceramics was constructed.As Ti O₂ content increases,when the A_g mode moves to low wave numbers,the B-O bond length increases,increasing the polarizability,thus enhancing the dielectric constant.The FWHM value of v₂ mode is related to the order degree of crystal structure,and the order degree is related to the value of Q×f which is a positive correlation.With the increase of Ti O₂ addition,x increases from 0 to 0.25,The value ofτ_f increased from-53.37 ppm/°C to-8.68 ppm/°C,ε_r grew from 5.42 to7.18,and when x=0.25,the ceramic obtained a near zero temperature coefficient:ε_r=7.18,Q×f=29,386 GHz,τ_f=-8.68 ppm/°C.