The advancement of millimeter-wave communication desires the ceramic substrate with low permittivity(ԑ_(r))to meet the requirements of high transmission rates,low latency and wide bandwidth.However,the thermal conduct...The advancement of millimeter-wave communication desires the ceramic substrate with low permittivity(ԑ_(r))to meet the requirements of high transmission rates,low latency and wide bandwidth.However,the thermal conductivity of most low-ԑ_(r)ceramics is too low to deal with heat dissipation in millimeter-wave applications.In this paper,we reported novel dielectric ceramics LiMSiO_(4)(M=Ga,Sc and Y)with excellent performances of low ԑ_(r)(<10)and high thermal conductivity(>6 W mK^(−1)).Their dielectric properties in both microwave and THz were investigated,where the LiGaSiO_(4)ceramic achieved the lowest ԑ_(r)of∼5.2,the LiScSiO_(4)ceramic presented extremely low loss(Q×f∼96,700 GHz,Q=1/dielectric loss,f is resonant frequency),and the LiYSiO_(4)ceramic showed a positive temperature coefficient of f(TCF∼+32 ppm℃^(−1)).The distinct dielectric behavior was subsequently studied by structure-performance relationship in terms of M-site cations and bond parameters using bond valence theory,Phillips-Van Vechten-Levine chemical bond theory and so on.Moreover,a 36 GHz microstrip array antenna was designed and simulated using the LiGaSiO_(4) ceramic substrate,obtaining high realized gain,high radiation efficiency and low sidelobe.The result demonstrated the great potential of LiMSiO_(4)-type dielectric ceramics in millimeter-wave communications.展开更多
In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal struc...In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.展开更多
The development of dielectric materials with low permittivity and low loss is a great challenge in wireless communication.In this study,LiLn(PO_(3))_(4)(Ln=La,Sm,Eu)ceramic systems were successfully prepared using the...The development of dielectric materials with low permittivity and low loss is a great challenge in wireless communication.In this study,LiLn(PO_(3))_(4)(Ln=La,Sm,Eu)ceramic systems were successfully prepared using the traditional solid-state method.X-ray diffraction analysis indicated that the LiLn(PO_(3))_(4)ceramics crystallized in a monoclinic structure when sintered at 850–940℃.The characteristic peak shifted to higher angles with variations in the Ln element,which was ascribed to a reduction in the cell volume.Further analysis by structure refinement revealed that the reduction in the cell volume resulted from the decrease in chemical bond lengths and the compression of[LiO_(4)]and[PO_(4)]tetrahedra.Remarkably,the LiLn(PO_(3))_(4)ceramic system displayed exceptional performance at low sintering temperatures(910–925℃),including a high quality factor(Q·f)of 41,607–75,968 GHz,low temperature coefficient of resonant frequency(τ_(f))ranging from−19.64 to−47.49 ppm/℃,low permittivity(ε_(r))between 5.04 and 5.26,and low density(3.04–3.26 g/cm^(3)).The application of Phillips–van Vechten–Levine(P–V–L)theory revealed that the increased Q·f value of the LiLn(PO_(3))_(4)systems can be attributed to the enhanced packing fraction,bond covalency,and lattice energy,and the stability of τ_(f) was associated with the increase in the bond energy.Furthermore,a prototype microstrip patch antenna using LiEu(PO_(3))_(4) ceramics was fabricated.The measurement results demonstrated excellent antenna performance with a bandwidth of 360 MHz and a peak gain of 5.11 dB at a central frequency of 5.08 GHz.Therefore,low-εr LiLn(PO_(3))_(4)ceramic systems are promising candidates for microwave/millimeter-wave communication.展开更多
In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass wa...In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi2O6 as the main phase. The second phases were CaSiO3 always existing and Li2SiO3 occurring at substitution content x > 0.05. Li+ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (εr) were investigated. The quality factor (Q × f) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τf) was influenced by MgO6 octahedral distortion and bond valence. Excellent dielectric properties of the CaMg1−xLi2xSi2O6 ceramic was exhibited at x = 0.05 with εr = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τf = −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.展开更多
Low permittivity microwave dielectric ceramics(MWDCs)are attracting great interest because of their promising applications in the new era of 5G and IoT.Although theoretical rules and computational methods are of pract...Low permittivity microwave dielectric ceramics(MWDCs)are attracting great interest because of their promising applications in the new era of 5G and IoT.Although theoretical rules and computational methods are of practical use for permittivity prediction,unsatisfactory predictability and universality impede rational design of new high-performance materials.In this work,based on a dataset of 254 single-phase microwave dielectric ceramics(MWDCs),machine learning(ML)methods established a high accuracy model for permittivity prediction and gave insights of quantitative chemistry/structureproperty relationships.We employed five commonly-used algorithms,and introduced 32 intrinsic chemical,structural and thermodynamic features which have correlations with permittivity for modeling.Machine learning results help identify the permittivity decisive factors,including polarizability per unit volume,average bond length,and average cell volume per atom.The feature-property relationships were discussed.The optimal model constructed by support vector regression with radial basis function kernel was validated its superior predictability and generalization by verification dataset.Low permittivity material systems were screened from a dataset of~3300 materials without reported microwave permittivity by high-throughput prediction using optimal model.Several predicted low permittivity ceramics were synthesized,and the experimental results agree well with ML prediction,which confirmed the reliability of the prediction model.展开更多
The rapid development of fifth-/sixth-generation telecommunication technologies has increased the demand for silicate ceramic materials with low permittivity and low dielectric loss.However,few silicate ceramics with ...The rapid development of fifth-/sixth-generation telecommunication technologies has increased the demand for silicate ceramic materials with low permittivity and low dielectric loss.However,few silicate ceramics with ultrahigh Q×f values(≥200,000 GHz)have been developed to date.In this study,a slight substitution of Ge^(4+)ions in MgSi_(1−x)Ge_(x)O_(3)(MSGx,x=0 to 0.6)ceramics caused a phase transition from clinoenstatite(x=0)to orthoenstatite(x=0.2),and the Q×f value increased from 70,600 GHz to 148,800 GHz.Following the phase transition,the cations change from a“compressed”state to a“rattle”state,and the lattice distortion continues to rise with x,resulting in the optimal microwave dielectric properties(ε_(r)=7.21,Q×f=259,300 GHz)of the MgSi0.5Ge0.5O3 ceramics.Significant discrepancies in the dielectric properties are found in the microwave and terahertz bands.There is an anomalous increase inεr and a decrease in the Q×f value in the terahertz band,which is due to the change in polar phonon modes revealed by the terahertz time-domain spectra.Consequently,MgSi_(0.7)Ge_(0.3)O_(3) ceramics display superior dielectric properties,withεr=7.02,Q×f=191,300 GHz in the terahertz band.These novel materials have the potential to serve as promising dielectric materials for future microwave or terahertz mobile communication systems.展开更多
This paper describes the solid-state production of a unique yellowish-grey microwave dielectric ceramic,Ca_(3)Fe_(2)Ge_(3)O_(12)(CFG).Rietveld refinement demonstrated that CFG corresponds to a cubic system(space group...This paper describes the solid-state production of a unique yellowish-grey microwave dielectric ceramic,Ca_(3)Fe_(2)Ge_(3)O_(12)(CFG).Rietveld refinement demonstrated that CFG corresponds to a cubic system(space group 230:Ia 3 d).The relative density of the ceramic initially increased and then decreased with the sintering temperature,reaching a maximum of 96.92%at 1330℃.According to scanning electron mi-croscopy and energy-dispersive spectroscopy results,the CFG ceramic grains are spherical and consistent in size;furthermore,they have distinct grain boundaries and a uniform distribution of the four con-stituent elements.The CFG ceramic has a superior crystal structure and a high crystallinity,according to transmission electron microscopy.Raman spectroscopy revealed that the Q×f value of the ceramic and the full width at half maximum of the Raman peak are negatively correlated.The ceramic possesses the best overall dielectric characteristics after sintering at 1330℃for 4 h:ε_(r)=10.31,Q×f=82636 GHz,andτ_(f)=-45.66×10^(-6)℃^(-1),showing that it is a promising candidate for use in mobile devices.展开更多
基金financially supported by the National Key Research and Development Program of China(No.2024YFE0103900)the National Natural Science Foundation of China(Nos.52202146 and 62271067)+1 种基金the Shaanxi Province University Joint Project(No.2023GXLH-019)the Fundamental Research Funds for the Central University.
文摘The advancement of millimeter-wave communication desires the ceramic substrate with low permittivity(ԑ_(r))to meet the requirements of high transmission rates,low latency and wide bandwidth.However,the thermal conductivity of most low-ԑ_(r)ceramics is too low to deal with heat dissipation in millimeter-wave applications.In this paper,we reported novel dielectric ceramics LiMSiO_(4)(M=Ga,Sc and Y)with excellent performances of low ԑ_(r)(<10)and high thermal conductivity(>6 W mK^(−1)).Their dielectric properties in both microwave and THz were investigated,where the LiGaSiO_(4)ceramic achieved the lowest ԑ_(r)of∼5.2,the LiScSiO_(4)ceramic presented extremely low loss(Q×f∼96,700 GHz,Q=1/dielectric loss,f is resonant frequency),and the LiYSiO_(4)ceramic showed a positive temperature coefficient of f(TCF∼+32 ppm℃^(−1)).The distinct dielectric behavior was subsequently studied by structure-performance relationship in terms of M-site cations and bond parameters using bond valence theory,Phillips-Van Vechten-Levine chemical bond theory and so on.Moreover,a 36 GHz microstrip array antenna was designed and simulated using the LiGaSiO_(4) ceramic substrate,obtaining high realized gain,high radiation efficiency and low sidelobe.The result demonstrated the great potential of LiMSiO_(4)-type dielectric ceramics in millimeter-wave communications.
基金Porject supported by National Natural Science Foundation of China (61761015, 11664008)Guangxi Natural Science Foundation(2018GXNSFFA050001, 2024GXNSFDA010060)High-Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes。
文摘In this paper,a novel SrEr_(2)O_(4)ceramic with relative densities exceeding 96% was synthesized by a conve ntional solid-state reaction method.Furthermo re,investigations of the correlations between its crystal structure,microstructure,and microwave dielectric properties were carried out.Rietveld refinements show that the SrEr_(2)O_(4)ceramics crystallize in the orthorhombic with the space group Pnam.The SrEr_(2)O_(4)ceramic sintered at 1575℃ exhibits the good performance of permittivity(ε_(r))=14.44,quality factor(Q × f)=23271 GHz,and resonant temperature frequency coefficient(τ_(f))=-21.5 ppm/℃,which is attributed to its high lattice energy,packing fraction,and relative density.In addition,to satisfy the requirement of temperature stability for communication devices,near-zero τ_(f) value is obtained by adding CaTiO_(3) at the cost of a small quality factor loss.The SrEr_(2)O_(4)+1.25 wt% CaTiO_(3) composite exhibits decent properties with ε_(r)=18.57,Q×f=19940 GHz,and T_(f)=+3.99 ppm/℃,making it an ideal candidate for microwave band applications.
基金National Natural Science Foundation of China(Nos.52272117 and 52171141)the National Key R&D Program of China(Nos.2022YFB3505104 and 2022YFB3706604)The authors are thankful to Professors Zeming Qi and Chuansheng Hu in IR beamline workstation of National Synchrotron Radiation Laboratory(NSRL)for the IR measurement.The authors thank Professor Lanling Zhao and Shiyanjia Lab(www.shiyanjia.com)for the support of first-principles calculations.
文摘The development of dielectric materials with low permittivity and low loss is a great challenge in wireless communication.In this study,LiLn(PO_(3))_(4)(Ln=La,Sm,Eu)ceramic systems were successfully prepared using the traditional solid-state method.X-ray diffraction analysis indicated that the LiLn(PO_(3))_(4)ceramics crystallized in a monoclinic structure when sintered at 850–940℃.The characteristic peak shifted to higher angles with variations in the Ln element,which was ascribed to a reduction in the cell volume.Further analysis by structure refinement revealed that the reduction in the cell volume resulted from the decrease in chemical bond lengths and the compression of[LiO_(4)]and[PO_(4)]tetrahedra.Remarkably,the LiLn(PO_(3))_(4)ceramic system displayed exceptional performance at low sintering temperatures(910–925℃),including a high quality factor(Q·f)of 41,607–75,968 GHz,low temperature coefficient of resonant frequency(τ_(f))ranging from−19.64 to−47.49 ppm/℃,low permittivity(ε_(r))between 5.04 and 5.26,and low density(3.04–3.26 g/cm^(3)).The application of Phillips–van Vechten–Levine(P–V–L)theory revealed that the increased Q·f value of the LiLn(PO_(3))_(4)systems can be attributed to the enhanced packing fraction,bond covalency,and lattice energy,and the stability of τ_(f) was associated with the increase in the bond energy.Furthermore,a prototype microstrip patch antenna using LiEu(PO_(3))_(4) ceramics was fabricated.The measurement results demonstrated excellent antenna performance with a bandwidth of 360 MHz and a peak gain of 5.11 dB at a central frequency of 5.08 GHz.Therefore,low-εr LiLn(PO_(3))_(4)ceramic systems are promising candidates for microwave/millimeter-wave communication.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.61771104 and U1809215).
文摘In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi2O6 as the main phase. The second phases were CaSiO3 always existing and Li2SiO3 occurring at substitution content x > 0.05. Li+ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (εr) were investigated. The quality factor (Q × f) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τf) was influenced by MgO6 octahedral distortion and bond valence. Excellent dielectric properties of the CaMg1−xLi2xSi2O6 ceramic was exhibited at x = 0.05 with εr = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τf = −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.
基金The authors would like to acknowledge the supports from the Key-Area Research and Development Program of Guangdong Province(2020B010176001)the National Natural Science Foundation of China(61871369)M.S.Ma acknowledges the Youth Innovation Promotion Association of CAS and Shanghai Rising-Star Program(20QA1410200).
文摘Low permittivity microwave dielectric ceramics(MWDCs)are attracting great interest because of their promising applications in the new era of 5G and IoT.Although theoretical rules and computational methods are of practical use for permittivity prediction,unsatisfactory predictability and universality impede rational design of new high-performance materials.In this work,based on a dataset of 254 single-phase microwave dielectric ceramics(MWDCs),machine learning(ML)methods established a high accuracy model for permittivity prediction and gave insights of quantitative chemistry/structureproperty relationships.We employed five commonly-used algorithms,and introduced 32 intrinsic chemical,structural and thermodynamic features which have correlations with permittivity for modeling.Machine learning results help identify the permittivity decisive factors,including polarizability per unit volume,average bond length,and average cell volume per atom.The feature-property relationships were discussed.The optimal model constructed by support vector regression with radial basis function kernel was validated its superior predictability and generalization by verification dataset.Low permittivity material systems were screened from a dataset of~3300 materials without reported microwave permittivity by high-throughput prediction using optimal model.Several predicted low permittivity ceramics were synthesized,and the experimental results agree well with ML prediction,which confirmed the reliability of the prediction model.
基金supported by the National Natural Science Foundation of China(Nos.51872160 and U23A6014)the Shuimu Tsinghua Scholar Program of Tsinghua University(No.2023SM245)the Postdoctoral Fellowship Program of the China Postdoctoral Science Fund(No.GZC20240782).
文摘The rapid development of fifth-/sixth-generation telecommunication technologies has increased the demand for silicate ceramic materials with low permittivity and low dielectric loss.However,few silicate ceramics with ultrahigh Q×f values(≥200,000 GHz)have been developed to date.In this study,a slight substitution of Ge^(4+)ions in MgSi_(1−x)Ge_(x)O_(3)(MSGx,x=0 to 0.6)ceramics caused a phase transition from clinoenstatite(x=0)to orthoenstatite(x=0.2),and the Q×f value increased from 70,600 GHz to 148,800 GHz.Following the phase transition,the cations change from a“compressed”state to a“rattle”state,and the lattice distortion continues to rise with x,resulting in the optimal microwave dielectric properties(ε_(r)=7.21,Q×f=259,300 GHz)of the MgSi0.5Ge0.5O3 ceramics.Significant discrepancies in the dielectric properties are found in the microwave and terahertz bands.There is an anomalous increase inεr and a decrease in the Q×f value in the terahertz band,which is due to the change in polar phonon modes revealed by the terahertz time-domain spectra.Consequently,MgSi_(0.7)Ge_(0.3)O_(3) ceramics display superior dielectric properties,withεr=7.02,Q×f=191,300 GHz in the terahertz band.These novel materials have the potential to serve as promising dielectric materials for future microwave or terahertz mobile communication systems.
基金supported by Natural Science Foundation of China(Grant Nos.61761015,11664008)Natural Science Foundation of Guangxi(Grant No 2018GXNSFFA050001)the High Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes.
文摘This paper describes the solid-state production of a unique yellowish-grey microwave dielectric ceramic,Ca_(3)Fe_(2)Ge_(3)O_(12)(CFG).Rietveld refinement demonstrated that CFG corresponds to a cubic system(space group 230:Ia 3 d).The relative density of the ceramic initially increased and then decreased with the sintering temperature,reaching a maximum of 96.92%at 1330℃.According to scanning electron mi-croscopy and energy-dispersive spectroscopy results,the CFG ceramic grains are spherical and consistent in size;furthermore,they have distinct grain boundaries and a uniform distribution of the four con-stituent elements.The CFG ceramic has a superior crystal structure and a high crystallinity,according to transmission electron microscopy.Raman spectroscopy revealed that the Q×f value of the ceramic and the full width at half maximum of the Raman peak are negatively correlated.The ceramic possesses the best overall dielectric characteristics after sintering at 1330℃for 4 h:ε_(r)=10.31,Q×f=82636 GHz,andτ_(f)=-45.66×10^(-6)℃^(-1),showing that it is a promising candidate for use in mobile devices.
