Stabilized ZnTiO4 was prepared by doping magnesium oxide through traditional solid state reaction. The experimental results indicate that zinc titanate crystals doped with magnesium oxide grow well and the decompositi...Stabilized ZnTiO4 was prepared by doping magnesium oxide through traditional solid state reaction. The experimental results indicate that zinc titanate crystals doped with magnesium oxide grow well and the decomposition into Zn2TiO4 and TiO2 is restrained through traditional solid state reaction, By adjusting molar ratio of MgO, better properties can be obtained The dielectric properties of the ceramics doped with 30% MgO（ molar percentage） sintered at 1060℃ are as follows：the value of quality factor is greater than 20000（6.5 GHz ）, the temperature coefficient of resonance frequency is about 2 ± 10^-6 /℃,the dielectric constant ranges from 180 to 22.Besides,it is proved that heat treatment can optimize microstructure and the value of quality factor, which increases from 23833.93 to 47584.00 after 2h of heat treatment at 1040℃.展开更多
The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this wor...The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.展开更多
This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent c...This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent comprehensive performance.The ceramics exhibit a predominant face-centered cubic disordered phase(Fd-3 m)sintered at 1200-1280°C,alongside an increased presence of the second phase MgTiO3 at higher temperatures.Remarkably,these ceramics demonstrate excellent microwave dielectric properties(ε_(r)=16.69,Q×f=88,230 GHz,andτ_(f)=−36.5 ppm/°C).Additionally,we have explored the addition of x wt%LiF(1≤x≤5)to the Li2 Mg_(6)ZnTi_(6)O_(20)ceramics to enhance their applicability.The ceramics feature a spinel structure for LiF contents up to 3 wt%,while higher LiF concentrations induce the formation of a secondary phase,LiTiO2,characterized by a rock salt structure.Notably,the lattice distortion induced by LiF leads to a constant decrease in ε_(r).A moderate degree of lattice distortion serves to enhance the lattice stability of ceramics,which is reflected in increased lattice energy.Excellent microwave dielectric properties(ε_(r)=16.23,Q×f=89,728 GHz,τ_(f)=−43.5 ppm/°C)were obtained for x=3 ceramic sintered at 1140°C.Even at x=5,the ceramic retains excellent microwave dielectric properties(ε_(r)=16.02,Q×f=63,079 GHz,τ_(f)=−26 ppm/°C)at a low sintering temperature of 900°C.This work realizes the multiple effects of LiF and confirms good chemical compatibility with silver for LTCC(low-temperature co-fired ceramics)applications.展开更多
The practical application of CaSmAlO_(4)microwave dielectric ceramics is limited by its low quality factor(Q×f)value and non-zero temperature coefficient resonant frequency(τ_(f))value.In this study,we introduce...The practical application of CaSmAlO_(4)microwave dielectric ceramics is limited by its low quality factor(Q×f)value and non-zero temperature coefficient resonant frequency(τ_(f))value.In this study,we introduced Mg^(2+)-Ti^(4+)ionic pairs into CaSmAlO_(4),along with an excess of 9%Sm_(2)O_(3).The Mg^(2+)-Ti^(4+)ionic pairs substituted Al^(3+),and two phases simultaneously coexisted in the ceramics:CaSmAlO_(4) and Sm_(2)O_(3).As the doping concentration of Mg^(2+)-Ti^(4+)ionic pairs increased,the relative permittivity exhibited an upward trend,while the quality factor and resonant frequency temperature coefficient first rose and then descended.Remarkably,0.09Sm_(2)O_(3)-0.91CaSmAl_(0.7)Mg_(0.15)-Ti_(0.15)O_(4) sintered at 1450℃ yielded excellent dielectric properties:ε_(r)=19.72,Q×f=72,936 GHz,and τ_(f)=-0.044 ppm·℃^(-1).The factors influencing the microwave dielectric properties of 0.09Sm_(2)O_(3)-0.91CaSmAlO_(4)ceramics were further examined by considering the crystal structure,grain size,Lichtenecker logarithmic rule,tolerance factor and packing fraction.展开更多
ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(...ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.展开更多
The effects of Li2O-MgO-B2O3 （LMB） glass additive on the sintering characteristics, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 ceramics were investigated. The experimental result...The effects of Li2O-MgO-B2O3 （LMB） glass additive on the sintering characteristics, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 ceramics were investigated. The experimental results demonstrate that the addition of LMB glass effectively lowers the sintering temperature of Li2MgTi3O8 ceramic from 1025 ℃ to 875 ℃ and induces no obvious degradation of the microwave dielectric properties. Typically, the 1.5%LMB glass-added Li2MgTi3O8 ceramic sintered at 875 ℃ for 4 h shows excellent microwave dielectric properties of Q×f=45403 GHz, εr=25.9 and τf≈0 ℃-1. The dielectric ceramic exhibits stability against the reaction with the Ag electrode, which indicates that the ceramics could be applied in multilayer microwave devices requiring low firing temperatures.展开更多
0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.With...0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = ＋8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.展开更多
The sintering behavior,microstructure and microwave dielectric properties of （1–x）CaTiO3–xLaAlO3 （x=0.1,0.3,0.5,0.7,0.9,respectively） ceramics were investigated systematically by thermogravimetry-differential th...The sintering behavior,microstructure and microwave dielectric properties of （1–x）CaTiO3–xLaAlO3 （x=0.1,0.3,0.5,0.7,0.9,respectively） ceramics were investigated systematically by thermogravimetry-differential thermal analysis （TG-DSC）,X-ray diffraction （XRD）,scanning electron microscopy （SEM） and a network analyzer.The result showed that forming temperature of the perovskite type crystal increased with increasing of x value.0.9CaTiO3-0.1LaAlO3 ceramics were sintered well from 1 400 to 1 550 oC,its bulk density increased with sintering temperature,and microwave dielectric properties of the ceramics at 1 400 oC was shown as follows： relative dielectric constant εr= 45.1,Q×f= 46 087 GHz and τf=–14.1×10–6/oC,respectively.But 0.7CaTiO3-0.3LaAlO3 ceramics were sintered well only when sintering temperature rose to 1 500 oC.（1–x）CaTiO3–xLaAlO3 （x=0.5,0.7 and 0.9,respectively） were not sintered well up to 1 550 oC and the sintered samples exhibited porous characteristic and with low bulk density.展开更多
La2O3 and SrO-doped CaO-MgO-Nb2O3-TiO2 system ceramics were prepared by solid-state ceramic technique.The microstructure and microwave dielectric properties of CaO-MgO-Nb2O5-TiO2-La2O3 cermics can be adjusted by varyi...La2O3 and SrO-doped CaO-MgO-Nb2O3-TiO2 system ceramics were prepared by solid-state ceramic technique.The microstructure and microwave dielectric properties of CaO-MgO-Nb2O5-TiO2-La2O3 cermics can be adjusted by varying the amount of La^3＋ or Sr^2＋ ions respectively.The replacement of Ca^2＋ by La^3＋ at A-site of the ceramics increases the quality factor Q value（ at 7.6GHz）as well as the temperature coefficient of resonant frequency τf and decreases the dielectric constant εr and the substitution of Sr^2＋ at A-site in this ceramics system exhibits opposite characteristics.The microwave properties of La^3＋,Sr^2＋-doped CaO-MgO-Nb2O5-TiO2 system ceramics depend on the degree of octahedral distortion inside materials.展开更多
A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,micros...A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.展开更多
Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2xTi18O54(x=2/3) ceramics.A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0<z<...Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2xTi18O54(x=2/3) ceramics.A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0<z<0.2 in Ba6-3xLa8+2x(Ti1-zZrz)18O54 ceramics.As Zr content exceeded this range,a secondary phase of Ba2ZrO4 was detected.This is correlated with the decrease of tolerance factor.As Zr content increased,there was an expansion of the b-axis and c-axis,and increase in the cell volume.Incorporation ...展开更多
La_2O_3-doped CaO-MgO-Nb_2O_5-TiO_2 system ceramics were prepared by solid-state ceramic technique. The microstructure and microwave dielectric properties of CaO-MgO-Nb_2O_5-TiO_2-La_2O_3 ceramics can be adjusted by v...La_2O_3-doped CaO-MgO-Nb_2O_5-TiO_2 system ceramics were prepared by solid-state ceramic technique. The microstructure and microwave dielectric properties of CaO-MgO-Nb_2O_5-TiO_2-La_2O_3 ceramics can be adjusted by varying the amount of La^(3+) ions. The results show that the replacement of Ca^(2+) by La^(3+) at A-site of the ceramics can increase the quality factor Q·f value as well as the temperature coefficient of resonant frequency τ_f and decrease the dielectric constant ε_r. With increase of La^(3+) contents, the dielectric constant decreases from 57 to 35 and Q·f value increases from 33400 GHz to 35000 GHz (at 7.6 GHz). Meanwhile, the temperature coefficient of resonant frequency is improved towards near zero. The dielectric properties of these compounds are related to octahedra tilting due to deficient vacancies at A-site.展开更多
The effect of La^3 ＋ , Sr^2＋ on the microstructure and microwave properties of CaO-MgO-Nb2O5-TiO2 system ceramics was investigated. The result shows that a single complex perovskite structure formed within investiga...The effect of La^3 ＋ , Sr^2＋ on the microstructure and microwave properties of CaO-MgO-Nb2O5-TiO2 system ceramics was investigated. The result shows that a single complex perovskite structure formed within investigated composition range in La^3＋ , Sr2-doped CaO-MgO-Nb2O5-TiO2 system ceramics. With increasing of La^3＋ , Sr^2＋ content, the structure of La^3＋ , Sr2-doped CaO-MgO-Nb2O5-TiO2 system ceramic respectively maintain orthorhombic type.展开更多
CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant freque...CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant frequency τf,making this system promising for microwave devices.However,its high synthesis temperature and sintering temperature limit its industrial applications.In our work,single phase0.7 CaTiO_(3)-0.3 Sm_(0.9)Nd_(0.1)AlO_(3)(7 CT-3 SNA) was synthesized via the sol-gel auto combustion method using citric acid as fuel at a relatively low temperature.After being calcined at 600℃ for 2 h,wellcrystallized 7 CT-3 SNA powders with 30-50 nm average particle size were achieved,suggesting good sintering activity.The new and narrow order band at about 800 cm^(-1) in the Raman spectra indicates a high ordering degree in the B site of 7 CT-3 SNA solid solution.Compared with the solid-state reaction method and co-precipitation method,the 0.7 CT-0.3 SNA ceramics fabricated by the current method possess a much lower calcination temperature,a similar εr value,and an improved Q × f value.The optimum microwave dielectric properties of εr=43.54,Q×f=54375 GHz,and τf=-6.3 ×10^(-6)/℃ are obtained for the CTSA ceramics derived from the sol-gel auto combustion process.Therefore,the 7 CT-3 SNA ceramics prepared in this study are potential dielectric materials for microwave applications,indicating that the sol-gel auto combustion method is a good alternative strategy for the fabrication of CaTiO_(3)-LnAlO_(3) ceramics.展开更多
The synthesis, structure and properties of a new A5B4O15-type cation-deficient perovskite Ba3La2Ti2Ta2O15 were discribed. The compound was prepared by the conventional solid-state reaction route. The phase and structu...The synthesis, structure and properties of a new A5B4O15-type cation-deficient perovskite Ba3La2Ti2Ta2O15 were discribed. The compound was prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）. The results reveal that the compound is successfully synthesized. The compound crystallizes in the trigonal system with unit cell parameter a=5.6730（2） A, c=11.6511（2） A, V=324.93（1） A^3 and Z=1. The microwave dielectric properties of the ceramic are studied using a network analyzer, and it shows a high dielectric constant of 45.1, a high quality factors with Q×fof21 029 GHz, and a positive τf of 5.3 ppm℃^-1.展开更多
In the present work,the structure and microwave dielectric properties of(Ba,Sr,Ca)HfO_(3)ceramics were systematically investigated to understand the general mechanism of tuning the temperature coefficient of resonant ...In the present work,the structure and microwave dielectric properties of(Ba,Sr,Ca)HfO_(3)ceramics were systematically investigated to understand the general mechanism of tuning the temperature coefficient of resonant frequency,tf in perovskite ceramics.Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)and Sr_(1-y)Ca_(y)HfO_(3)could form continuous solid solutions while the solid solubility of Ca in Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)was about 20%(in mole).tf changed nonlinearly with increasing tolerance factor as the result of competition between the increase in the restoring force on the ions and the increase in polarizability.Under the guidance of three microscopic mechanisms affecting tf,a preliminary attempt was made to explore the suitable parameters to predict the variation trend of tf.Normalized ionic radii and the tf values of the end members were selected as independent variables,and tf was calculated by using multiple linear regression method.For Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)and Sr_(1-y)Ca_(y)HfO_(3)with orthorhombic structures,the root mean square error between the calculated and measured tf was only 6.8×10℃^(-1).The good agreement between the calculated tf values and the measured ones in Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)ceramics confirmed its validity where three elements jointly occupy A-site,but it only works when there is no structural phase transition.Progresses in this researchfield would not only deepen our understanding of mechanism of regulating properties in multi-ion solid solutions,but also boost the developments of closely relatedfields such as machine learning-assisted design and high-entropy ceramics.Finally,a good combination of microwave dielectric properties was achieved in Sr_(0.15)Ca_(0.85)Hf_(0.96)Ti_(0.040)O_(3):εr=27.8,Qf=36,470 GHz,τf=+5×10^(-6)℃^(-1).展开更多
Dense microwave dielectric ceramics of Sr_(1-x)Ca_(x)Tm_(2)O_(4)(x=0.025-0.300)were fabricated via the conventional solid-state reaction method.Systematical investigations on the impact of Ca^(2+)on their microstructu...Dense microwave dielectric ceramics of Sr_(1-x)Ca_(x)Tm_(2)O_(4)(x=0.025-0.300)were fabricated via the conventional solid-state reaction method.Systematical investigations on the impact of Ca^(2+)on their microstructures,sintering behaviors,and microwave dielectric properties were detailly conducted.The combined XRD data and subsequent refinement demonstrated that all samples exhibited structural conformity with SrTm_(2)O_(4) and belonged to Pnam space group.Calculations were executed to illustrate the evolution of performance-related chemical bonding parameters associated with Ca^(2+)on the basis of the PVL theory.High density,lattice energy and narrow full width at half maximum of Raman modes contribute to a performance boost of around 14%.Excellent dielectric properties of Sr_(0.95)Ca_(0.05)Tm_(2)O_(4),including relative permittivity of 15.97,quality factor of 47,142 GHz,and temperature coefficient of resonant frequency of−24.65×10^(−6)℃^(−1).Furthermore,Sr_(0.95)Ca_(0.05)Tm_(2)O_(4) ceramics were designed as rectangular dielectric resonator antennas with 388 MHz bandwidth at the center frequency of 6.525 GHz,along with high simulated radiation efficiency(≥90%)and realized gain(5.80-6.47 dBi),which suggests their considerable potential in 5G communication applications.展开更多
Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range.In high-density packages,dielectric substrates ceramics must possess high thermal conductivity to...Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range.In high-density packages,dielectric substrates ceramics must possess high thermal conductivity to efficiently dissipate heat.However,achieving adequate thermal conductivity(k)in ceramics sintered at low temperatures is challenging.In this study,we employed the cold sintering process(CSP)to fabricate Li_(2)MoO_(4)-x%Al_(2)O_(3)(0≤x≤80,in volume)ceramics under 200 MPa pressure at 150℃.The Li_(2)MoO_(4)-40%Al_(2)O_(3)composite exhibited significantly enhanced k of 5.4 W·m^(-1)·K^(-1),an 80%increase compared to pure Li_(2)MoO_(4)ceramic with k of 3 W·m^(-1)·K^(-1).At 40%Al_(2)O_(3)content,the Li_(2)MoO_(4)eAl_(2)O_(3)ceramic demonstrated notable microwave properties(ε~6.67,Q×f~17,846 GHz,tf~^(-1)05×10^(-6)℃^(-1)).Additionally,simulation of a microstrip patch antenna for 5 GHz applications using Li_(2)MoO_(4)-20%Al_(2)O_(3)ceramic as dielectric substrate via Finite Element Simulation software showed excellent performance,with radiation efficiency exceeding 99%and low return loss(S_(11)<-30 dB)at both 4.9 GHz and 28.0 GHz center frequencies.These findings underscore the suitability of Li_(2)MoO_(4)eAl_(2)O_(3)ceramics for microwave dielectric substrate.展开更多
Microwave dielectric ceramics(MWDCs)with a high Q×f value can improve the performance of radio frequency components like resonators,filters,antennas and so on.However,the quantitative structureproperty relationsh...Microwave dielectric ceramics(MWDCs)with a high Q×f value can improve the performance of radio frequency components like resonators,filters,antennas and so on.However,the quantitative structureproperty relationship(QSPR)for the Q×f value is complicated and unclear.In this study,machine learning methods were used to explore the QSPR and build up Q×f value prediction model based on a dataset of 164 ABO_(4)-type MWDCs.We employed five commonly-used algorithms for modeling,and 35 structural features having correlations with Q×f value were used as input.In order to describe structure from both global and local perspectives,three different feature construction methods were compared.The optimal model based on support vector regression with radial basis function kernel shows good performances and generalization capability.The features contained in the optimal model are primitive cell volume,molecular dielectric polarizability and electronegativity with A-and B-site mean method.The relationships between property and structure were discussed.The model used for the Q×f value prediction of tetragonal scheelite shows excellent performances(R^(2)=0.8115 and RMSE=8362.73 GHz),but it needs auxiliary features of average bond length,theoretical density and polarizability per unit volume for monoclinic wolframite ceramics to improve model prediction ability.展开更多
With the rapid deployment of 5G and the emergence of 6G technologies,the demand for high-performance microwave dielectric ceramics(MWDCs)has increased.This study developed Y_(3)MgAl_(3)GeO_(12)(YMAG)garnet ceramics to...With the rapid deployment of 5G and the emergence of 6G technologies,the demand for high-performance microwave dielectric ceramics(MWDCs)has increased.This study developed Y_(3)MgAl_(3)GeO_(12)(YMAG)garnet ceramics to meet 5G/6G requirements for low signal delay,low loss,and high-temperature stability.YMAG ceramics synthesized via a solid-state reaction were characterized for phase composition,crystal structure,microstructure,and microwave dielectric properties.The results revealed that YMAG ceramics exhibited excellent microwave performance:a permittivity(εr)of 9.86,a quality factor(Q×f)of 89,000 GHz,and a temperature coefficient of resonant frequency(τf)of−40 ppm/°C.Far-infrared and terahertz(THz)spectroscopic analyses verified the low intrinsic dielectric loss and frequency-stable dielectric characteristics of the material in high-frequency ranges.Temperature-dependent dielectric measurements coupled with thermal expansion studies revealed outstanding stability in this material,as evidenced by its low coefficient of thermal expansion(αL=9.13 ppm/°C).To attain near-zeroτf,we added TiO_(2)as a positiveτf compensation agent.This strategy effectively tuned theτf value to within|τf|<10 ppm/°C while preserving excellent microwave dielectric performance(Q×f≈43,000 GHz).Furthermore,a rectangular dielectric resonator antenna(DRA)designed with the optimized YMAG–TiO_(2)composite demonstrated excellent impedance matching(VSWR=1.02)and high radiation efficiency(>90%)in the X-band(10.21 GHz),validating its potential for 5G/6G applications.This work provides a novel approach for developing high-performance MWDCs for next-generation communication technologies and emphasizes the critical role of material design and optimization in achieving superior microwave properties.展开更多
基金SUPPORTED BY NATIONAL NATURAL SCIENCE FOUNDATION OF CHINA( NO. 50172035).
文摘Stabilized ZnTiO4 was prepared by doping magnesium oxide through traditional solid state reaction. The experimental results indicate that zinc titanate crystals doped with magnesium oxide grow well and the decomposition into Zn2TiO4 and TiO2 is restrained through traditional solid state reaction, By adjusting molar ratio of MgO, better properties can be obtained The dielectric properties of the ceramics doped with 30% MgO（ molar percentage） sintered at 1060℃ are as follows：the value of quality factor is greater than 20000（6.5 GHz ）, the temperature coefficient of resonance frequency is about 2 ± 10^-6 /℃,the dielectric constant ranges from 180 to 22.Besides,it is proved that heat treatment can optimize microstructure and the value of quality factor, which increases from 23833.93 to 47584.00 after 2h of heat treatment at 1040℃.
基金National Natural Science Foundation of China (52302140)Major Scientific and Technological Innovation Project of Wenzhou (ZG2023040, ZG2023042)Joint Funds of the National Natural Science Foundation of China Key Program (U21B2068)。
文摘The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.
基金supported by the National Natural Science Foundation of China(No.52102129)the Hunan Provincial Natural Science Foundation of China(No.2023JJ30138)the Science and Technology Innovation Program of Hunan Province(No.2023RC3094).
文摘This study designs and synthesizes highly dense Li2 Mg_(6)ZnTi_(6)O_(20)microwave dielectric ceramics based on a high-entropy strategy,focusing on achieving stable structures,low sintering temperatures,and excellent comprehensive performance.The ceramics exhibit a predominant face-centered cubic disordered phase(Fd-3 m)sintered at 1200-1280°C,alongside an increased presence of the second phase MgTiO3 at higher temperatures.Remarkably,these ceramics demonstrate excellent microwave dielectric properties(ε_(r)=16.69,Q×f=88,230 GHz,andτ_(f)=−36.5 ppm/°C).Additionally,we have explored the addition of x wt%LiF(1≤x≤5)to the Li2 Mg_(6)ZnTi_(6)O_(20)ceramics to enhance their applicability.The ceramics feature a spinel structure for LiF contents up to 3 wt%,while higher LiF concentrations induce the formation of a secondary phase,LiTiO2,characterized by a rock salt structure.Notably,the lattice distortion induced by LiF leads to a constant decrease in ε_(r).A moderate degree of lattice distortion serves to enhance the lattice stability of ceramics,which is reflected in increased lattice energy.Excellent microwave dielectric properties(ε_(r)=16.23,Q×f=89,728 GHz,τ_(f)=−43.5 ppm/°C)were obtained for x=3 ceramic sintered at 1140°C.Even at x=5,the ceramic retains excellent microwave dielectric properties(ε_(r)=16.02,Q×f=63,079 GHz,τ_(f)=−26 ppm/°C)at a low sintering temperature of 900°C.This work realizes the multiple effects of LiF and confirms good chemical compatibility with silver for LTCC(low-temperature co-fired ceramics)applications.
基金financially supported by the National Key Research Program of China (No.2021YFB3800601)the Basic Science Center Project of the National Natural Science Foundation of China (No.52388201)the Fellowship of China Postdoctoral Science Foundation (No.2022M710073)。
文摘The practical application of CaSmAlO_(4)microwave dielectric ceramics is limited by its low quality factor(Q×f)value and non-zero temperature coefficient resonant frequency(τ_(f))value.In this study,we introduced Mg^(2+)-Ti^(4+)ionic pairs into CaSmAlO_(4),along with an excess of 9%Sm_(2)O_(3).The Mg^(2+)-Ti^(4+)ionic pairs substituted Al^(3+),and two phases simultaneously coexisted in the ceramics:CaSmAlO_(4) and Sm_(2)O_(3).As the doping concentration of Mg^(2+)-Ti^(4+)ionic pairs increased,the relative permittivity exhibited an upward trend,while the quality factor and resonant frequency temperature coefficient first rose and then descended.Remarkably,0.09Sm_(2)O_(3)-0.91CaSmAl_(0.7)Mg_(0.15)-Ti_(0.15)O_(4) sintered at 1450℃ yielded excellent dielectric properties:ε_(r)=19.72,Q×f=72,936 GHz,and τ_(f)=-0.044 ppm·℃^(-1).The factors influencing the microwave dielectric properties of 0.09Sm_(2)O_(3)-0.91CaSmAlO_(4)ceramics were further examined by considering the crystal structure,grain size,Lichtenecker logarithmic rule,tolerance factor and packing fraction.
基金National Natural Science Foundation of China (U24A2052)Shanghai Eastern Talent Plan。
文摘ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.
基金Project(2010GXNSFA013029)supported by National Undergraduates Innovating Experimentation Project of ChinaProject(101059529)supported by Natural Science Foundation of Guangxi,China
文摘The effects of Li2O-MgO-B2O3 （LMB） glass additive on the sintering characteristics, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 ceramics were investigated. The experimental results demonstrate that the addition of LMB glass effectively lowers the sintering temperature of Li2MgTi3O8 ceramic from 1025 ℃ to 875 ℃ and induces no obvious degradation of the microwave dielectric properties. Typically, the 1.5%LMB glass-added Li2MgTi3O8 ceramic sintered at 875 ℃ for 4 h shows excellent microwave dielectric properties of Q×f=45403 GHz, εr=25.9 and τf≈0 ℃-1. The dielectric ceramic exhibits stability against the reaction with the Ag electrode, which indicates that the ceramics could be applied in multilayer microwave devices requiring low firing temperatures.
基金Project supported by Anhui Provincial Natural Science Foundation(1608085ME92)
文摘0.5 Ca（0.6La0.267TiO3-0.5 Ca（Mg1/3Nb2/3）O3（5 CLT-5 CMN） ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = ＋8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.
基金Project supported by the Sci-Tech Development Support Program of Jiangsu Province (BE2008653)Major Basic Research Project of Natural Science Foundation of Jiangsu Provincial Education Department (08KJA430005)
文摘The sintering behavior,microstructure and microwave dielectric properties of （1–x）CaTiO3–xLaAlO3 （x=0.1,0.3,0.5,0.7,0.9,respectively） ceramics were investigated systematically by thermogravimetry-differential thermal analysis （TG-DSC）,X-ray diffraction （XRD）,scanning electron microscopy （SEM） and a network analyzer.The result showed that forming temperature of the perovskite type crystal increased with increasing of x value.0.9CaTiO3-0.1LaAlO3 ceramics were sintered well from 1 400 to 1 550 oC,its bulk density increased with sintering temperature,and microwave dielectric properties of the ceramics at 1 400 oC was shown as follows： relative dielectric constant εr= 45.1,Q×f= 46 087 GHz and τf=–14.1×10–6/oC,respectively.But 0.7CaTiO3-0.3LaAlO3 ceramics were sintered well only when sintering temperature rose to 1 500 oC.（1–x）CaTiO3–xLaAlO3 （x=0.5,0.7 and 0.9,respectively） were not sintered well up to 1 550 oC and the sintered samples exhibited porous characteristic and with low bulk density.
文摘La2O3 and SrO-doped CaO-MgO-Nb2O3-TiO2 system ceramics were prepared by solid-state ceramic technique.The microstructure and microwave dielectric properties of CaO-MgO-Nb2O5-TiO2-La2O3 cermics can be adjusted by varying the amount of La^3＋ or Sr^2＋ ions respectively.The replacement of Ca^2＋ by La^3＋ at A-site of the ceramics increases the quality factor Q value（ at 7.6GHz）as well as the temperature coefficient of resonant frequency τf and decreases the dielectric constant εr and the substitution of Sr^2＋ at A-site in this ceramics system exhibits opposite characteristics.The microwave properties of La^3＋,Sr^2＋-doped CaO-MgO-Nb2O5-TiO2 system ceramics depend on the degree of octahedral distortion inside materials.
基金the Chengdu University of Technology(Grant No.KYQD201907728)。
文摘A series of nominal compositions MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)(x=0,0.04,0.08,0.12,0.16,and 0.20)ceramics were successfully prepared via the conventional solid-state reaction route.The phase compositions,microstructures,and microwave dielectric properties were investigated.The results of x-ray diffraction(XRD)and scanning electron microscopy(SEM)showed that a single phase of MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with a spinel structure was obtained at x≤0.12,whereas the second phase of MgTi_(2)O_(5)appeared when x>0.12.The cell parameters were obtained by XRD refinement.As the x values increased,the unit cell volume kept expanding.This phenomenon could be attributed to the partial substitution of(Li_(1/3)Ti_(2/3))^(3+)for Al^(3+).Results showed that(Li_(1/3)Ti_(2/3))^(3+)doping into MgAl_(2)O_(4)spinel ceramics effectively reduced the sintering temperature and improved the quality factor(Q_f)values.Good microwave dielectric properties were achieved for a sample at x=0.20 sintering at 1500℃in air for 4 h:dielectric constantε_(r)=8.78,temperature coefficient of resonant frequencyτ_(f)=-85 ppm/℃,and Q_(f)=62300 GHz.The Q_(f)value of the x=0.20 sample was about 2 times higher than that of pure MgAl_(2)O_(4)ceramics(31600 GHz).Thus,MgAl_(2-x)(Li_(1/3)Ti_(2/3))_(x)O_(4)ceramics with excellent microwave dielectric properties can be applied to 5G communications.
文摘Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2xTi18O54(x=2/3) ceramics.A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0<z<0.2 in Ba6-3xLa8+2x(Ti1-zZrz)18O54 ceramics.As Zr content exceeded this range,a secondary phase of Ba2ZrO4 was detected.This is correlated with the decrease of tolerance factor.As Zr content increased,there was an expansion of the b-axis and c-axis,and increase in the cell volume.Incorporation ...
基金Project supported by the National Science Foundation (50272044) of China
文摘La_2O_3-doped CaO-MgO-Nb_2O_5-TiO_2 system ceramics were prepared by solid-state ceramic technique. The microstructure and microwave dielectric properties of CaO-MgO-Nb_2O_5-TiO_2-La_2O_3 ceramics can be adjusted by varying the amount of La^(3+) ions. The results show that the replacement of Ca^(2+) by La^(3+) at A-site of the ceramics can increase the quality factor Q·f value as well as the temperature coefficient of resonant frequency τ_f and decrease the dielectric constant ε_r. With increase of La^(3+) contents, the dielectric constant decreases from 57 to 35 and Q·f value increases from 33400 GHz to 35000 GHz (at 7.6 GHz). Meanwhile, the temperature coefficient of resonant frequency is improved towards near zero. The dielectric properties of these compounds are related to octahedra tilting due to deficient vacancies at A-site.
文摘The effect of La^3 ＋ , Sr^2＋ on the microstructure and microwave properties of CaO-MgO-Nb2O5-TiO2 system ceramics was investigated. The result shows that a single complex perovskite structure formed within investigated composition range in La^3＋ , Sr2-doped CaO-MgO-Nb2O5-TiO2 system ceramics. With increasing of La^3＋ , Sr^2＋ content, the structure of La^3＋ , Sr2-doped CaO-MgO-Nb2O5-TiO2 system ceramic respectively maintain orthorhombic type.
基金Project supported by the Natural Science Foundation of Anhui Provincial Education Department (KJ2019A0054)the Student Research and Training Program of Anhui University of Technology (2020008)。
文摘CaTiO_(3)-LnAlO_(3)(Ln=La,Nd,Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr,a high quality factor Q×f,and a small temperature coefficient of resonant frequency τf,making this system promising for microwave devices.However,its high synthesis temperature and sintering temperature limit its industrial applications.In our work,single phase0.7 CaTiO_(3)-0.3 Sm_(0.9)Nd_(0.1)AlO_(3)(7 CT-3 SNA) was synthesized via the sol-gel auto combustion method using citric acid as fuel at a relatively low temperature.After being calcined at 600℃ for 2 h,wellcrystallized 7 CT-3 SNA powders with 30-50 nm average particle size were achieved,suggesting good sintering activity.The new and narrow order band at about 800 cm^(-1) in the Raman spectra indicates a high ordering degree in the B site of 7 CT-3 SNA solid solution.Compared with the solid-state reaction method and co-precipitation method,the 0.7 CT-0.3 SNA ceramics fabricated by the current method possess a much lower calcination temperature,a similar εr value,and an improved Q × f value.The optimum microwave dielectric properties of εr=43.54,Q×f=54375 GHz,and τf=-6.3 ×10^(-6)/℃ are obtained for the CTSA ceramics derived from the sol-gel auto combustion process.Therefore,the 7 CT-3 SNA ceramics prepared in this study are potential dielectric materials for microwave applications,indicating that the sol-gel auto combustion method is a good alternative strategy for the fabrication of CaTiO_(3)-LnAlO_(3) ceramics.
基金Funded by the National Natural Science Foundation of China(No.20571059 and No.50572078)Opening Foundation of Key Laboratory of New Processing Technology for Nonferrous Metals and Materials,Ministry of Education
文摘The synthesis, structure and properties of a new A5B4O15-type cation-deficient perovskite Ba3La2Ti2Ta2O15 were discribed. The compound was prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）. The results reveal that the compound is successfully synthesized. The compound crystallizes in the trigonal system with unit cell parameter a=5.6730（2） A, c=11.6511（2） A, V=324.93（1） A^3 and Z=1. The microwave dielectric properties of the ceramic are studied using a network analyzer, and it shows a high dielectric constant of 45.1, a high quality factors with Q×fof21 029 GHz, and a positive τf of 5.3 ppm℃^-1.
基金by National Natural Foundation of China under grant Nos.U20A2024352372127.
文摘In the present work,the structure and microwave dielectric properties of(Ba,Sr,Ca)HfO_(3)ceramics were systematically investigated to understand the general mechanism of tuning the temperature coefficient of resonant frequency,tf in perovskite ceramics.Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)and Sr_(1-y)Ca_(y)HfO_(3)could form continuous solid solutions while the solid solubility of Ca in Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)was about 20%(in mole).tf changed nonlinearly with increasing tolerance factor as the result of competition between the increase in the restoring force on the ions and the increase in polarizability.Under the guidance of three microscopic mechanisms affecting tf,a preliminary attempt was made to explore the suitable parameters to predict the variation trend of tf.Normalized ionic radii and the tf values of the end members were selected as independent variables,and tf was calculated by using multiple linear regression method.For Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)and Sr_(1-y)Ca_(y)HfO_(3)with orthorhombic structures,the root mean square error between the calculated and measured tf was only 6.8×10℃^(-1).The good agreement between the calculated tf values and the measured ones in Ba1_(-x-y)Sr_(x)Ca_(y)HfO_(3)ceramics confirmed its validity where three elements jointly occupy A-site,but it only works when there is no structural phase transition.Progresses in this researchfield would not only deepen our understanding of mechanism of regulating properties in multi-ion solid solutions,but also boost the developments of closely relatedfields such as machine learning-assisted design and high-entropy ceramics.Finally,a good combination of microwave dielectric properties was achieved in Sr_(0.15)Ca_(0.85)Hf_(0.96)Ti_(0.040)O_(3):εr=27.8,Qf=36,470 GHz,τf=+5×10^(-6)℃^(-1).
基金supported by National Natural Science Foundation of China(No.61761015)Guangxi Natural Science Foundation(No.2024GXNSFDA010060)Guilin Science Research and Technology Development Plan Project(20230120-8).
文摘Dense microwave dielectric ceramics of Sr_(1-x)Ca_(x)Tm_(2)O_(4)(x=0.025-0.300)were fabricated via the conventional solid-state reaction method.Systematical investigations on the impact of Ca^(2+)on their microstructures,sintering behaviors,and microwave dielectric properties were detailly conducted.The combined XRD data and subsequent refinement demonstrated that all samples exhibited structural conformity with SrTm_(2)O_(4) and belonged to Pnam space group.Calculations were executed to illustrate the evolution of performance-related chemical bonding parameters associated with Ca^(2+)on the basis of the PVL theory.High density,lattice energy and narrow full width at half maximum of Raman modes contribute to a performance boost of around 14%.Excellent dielectric properties of Sr_(0.95)Ca_(0.05)Tm_(2)O_(4),including relative permittivity of 15.97,quality factor of 47,142 GHz,and temperature coefficient of resonant frequency of−24.65×10^(−6)℃^(−1).Furthermore,Sr_(0.95)Ca_(0.05)Tm_(2)O_(4) ceramics were designed as rectangular dielectric resonator antennas with 388 MHz bandwidth at the center frequency of 6.525 GHz,along with high simulated radiation efficiency(≥90%)and realized gain(5.80-6.47 dBi),which suggests their considerable potential in 5G communication applications.
基金supported by National Natural Science Foundation of China(No.52361165625)Shenzhen Science and Technology Program,Guangdong Province,China(Nos.KQTD20180411143514543,JCYJ20220818100613029,and JSGGZD20220822095603006)We acknowledge the support of Project 2019CX01C079 of Guangdong Province。
文摘Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range.In high-density packages,dielectric substrates ceramics must possess high thermal conductivity to efficiently dissipate heat.However,achieving adequate thermal conductivity(k)in ceramics sintered at low temperatures is challenging.In this study,we employed the cold sintering process(CSP)to fabricate Li_(2)MoO_(4)-x%Al_(2)O_(3)(0≤x≤80,in volume)ceramics under 200 MPa pressure at 150℃.The Li_(2)MoO_(4)-40%Al_(2)O_(3)composite exhibited significantly enhanced k of 5.4 W·m^(-1)·K^(-1),an 80%increase compared to pure Li_(2)MoO_(4)ceramic with k of 3 W·m^(-1)·K^(-1).At 40%Al_(2)O_(3)content,the Li_(2)MoO_(4)eAl_(2)O_(3)ceramic demonstrated notable microwave properties(ε~6.67,Q×f~17,846 GHz,tf~^(-1)05×10^(-6)℃^(-1)).Additionally,simulation of a microstrip patch antenna for 5 GHz applications using Li_(2)MoO_(4)-20%Al_(2)O_(3)ceramic as dielectric substrate via Finite Element Simulation software showed excellent performance,with radiation efficiency exceeding 99%and low return loss(S_(11)<-30 dB)at both 4.9 GHz and 28.0 GHz center frequencies.These findings underscore the suitability of Li_(2)MoO_(4)eAl_(2)O_(3)ceramics for microwave dielectric substrate.
基金the Postdoctoral Fellowship Program of China Postdoctoral Science Fund(GZC20232825)the Outstanding Academic/Technical Leader Project in Shanghai Plan of Action on Science and Technology Innovation(23XD1404600).
文摘Microwave dielectric ceramics(MWDCs)with a high Q×f value can improve the performance of radio frequency components like resonators,filters,antennas and so on.However,the quantitative structureproperty relationship(QSPR)for the Q×f value is complicated and unclear.In this study,machine learning methods were used to explore the QSPR and build up Q×f value prediction model based on a dataset of 164 ABO_(4)-type MWDCs.We employed five commonly-used algorithms for modeling,and 35 structural features having correlations with Q×f value were used as input.In order to describe structure from both global and local perspectives,three different feature construction methods were compared.The optimal model based on support vector regression with radial basis function kernel shows good performances and generalization capability.The features contained in the optimal model are primitive cell volume,molecular dielectric polarizability and electronegativity with A-and B-site mean method.The relationships between property and structure were discussed.The model used for the Q×f value prediction of tetragonal scheelite shows excellent performances(R^(2)=0.8115 and RMSE=8362.73 GHz),but it needs auxiliary features of average bond length,theoretical density and polarizability per unit volume for monoclinic wolframite ceramics to improve model prediction ability.
基金supported by the Guangxi Science and Technology Plan Project(No.GuikeAD25069100)the Guangxi Natural Science Foundation Project(No.2024GXNSFDA010060).
文摘With the rapid deployment of 5G and the emergence of 6G technologies,the demand for high-performance microwave dielectric ceramics(MWDCs)has increased.This study developed Y_(3)MgAl_(3)GeO_(12)(YMAG)garnet ceramics to meet 5G/6G requirements for low signal delay,low loss,and high-temperature stability.YMAG ceramics synthesized via a solid-state reaction were characterized for phase composition,crystal structure,microstructure,and microwave dielectric properties.The results revealed that YMAG ceramics exhibited excellent microwave performance:a permittivity(εr)of 9.86,a quality factor(Q×f)of 89,000 GHz,and a temperature coefficient of resonant frequency(τf)of−40 ppm/°C.Far-infrared and terahertz(THz)spectroscopic analyses verified the low intrinsic dielectric loss and frequency-stable dielectric characteristics of the material in high-frequency ranges.Temperature-dependent dielectric measurements coupled with thermal expansion studies revealed outstanding stability in this material,as evidenced by its low coefficient of thermal expansion(αL=9.13 ppm/°C).To attain near-zeroτf,we added TiO_(2)as a positiveτf compensation agent.This strategy effectively tuned theτf value to within|τf|<10 ppm/°C while preserving excellent microwave dielectric performance(Q×f≈43,000 GHz).Furthermore,a rectangular dielectric resonator antenna(DRA)designed with the optimized YMAG–TiO_(2)composite demonstrated excellent impedance matching(VSWR=1.02)and high radiation efficiency(>90%)in the X-band(10.21 GHz),validating its potential for 5G/6G applications.This work provides a novel approach for developing high-performance MWDCs for next-generation communication technologies and emphasizes the critical role of material design and optimization in achieving superior microwave properties.
