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
Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suita...Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.展开更多
The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and mi...The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.展开更多
The effects of low-κ and high-κ spacer were investigated on the novel tunnel dielectric based tunnel field-effect transistor(TD-FET) mainly based upon ultra-thin dielectric direct tunneling mechanism. Drive currents...The effects of low-κ and high-κ spacer were investigated on the novel tunnel dielectric based tunnel field-effect transistor(TD-FET) mainly based upon ultra-thin dielectric direct tunneling mechanism. Drive currents consist of direct tunneling current and band-to-band tunneling(BTBT) current. Meanwhile, tunneling position of the TD-FET differs from conventional tunnel-FET in which the electron and hole tunneling occur at intermediate rather than surface in channel(or source-channel junction under gate dielectric). The 2-D nature of TD-FET current flow is also discussed that the on-current is degraded with an increase in the spacer width. BTBT current will not begin to play part in tunneling current until gate voltage is 0.2 V. We clearly identify the influence of the tunneling dielectric layer and spacer electrostatic field on the device characteristics by numerical simulations. The inserted Si_3N_4 tunnel layer between P+ region and N+ region can significantly shorten the direct and band-to-band tunneling path, so a reduced subthreshold slope(Ss) and a high on-current can be achieved. Above all the ambipolar current is effectively suppressed, thus reducing off-current. TD-FET demonstrates excellent performance for low-power applications.展开更多
The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diff...The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of B203 causes the increase of the contents of [BO3], [BO4] and [SiO4], which deduces the increase of CaB204 and a-SiO2 and the decrease of CaSiO3 correspondingly. No new phase is observed throughout the entire experiments. A bulk density of 2.54 g/cm3, a thermal expansion coefficient value of 11.95× 10-6 ℃-1 （20-500℃）, a dielectric constant er value of 6.42 and a dielectric loss tanδ value of 0.000 9 （measured at 9.7 GHz） are obtained for CBS glass ceramics containing 35%-B203 （mass fraction） sintered at 850 ℃ for 15 min.展开更多
The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-...The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-doped TiO2-based varistor ceramics were fabricated by sintering at 1 250 ℃ for 0.5-5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cma decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 1l5 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0-3.0 h considering both nonlinear electrical behavior and dielectric properties.展开更多
The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential ther...The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.展开更多
Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The result...Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.展开更多
Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based o...Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green＇s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green＇s function can be divided into two parts： primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.展开更多
CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning ...CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.展开更多
Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small vol...Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.展开更多
The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was sign...The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was significantly reduced under nano-gap conditions and the optimal discharge voltage was 2 kV.Then,the anodic bonding and dielectric barrier discharge activated bonding were performed in comparison experiments,and the bonding strength was characterized by tensile failure test.The results showed that the bonding strength was higher under the nano-gap dielectric barrier discharge.This process completed 110°C ultra-low temperature anodic bonding and the bonding strength reached 2 MPa.Finally,the mechanism of promoting bonding after activation is also discussed.展开更多
The effects of alkali oxides （Na2O and K2O addition on both the sintering behavior and dielectric properties of Ca-AI-B-Si-O glass/Al2O3 composites were investigated by Fourier transform infrared spectroscopy （FTIR...The effects of alkali oxides （Na2O and K2O addition on both the sintering behavior and dielectric properties of Ca-AI-B-Si-O glass/Al2O3 composites were investigated by Fourier transform infrared spectroscopy （FTIR）, differential scanning calorimeter （DSC）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of alkali oxides in the glass causes the decrease of [SiO4], which results in the decrease of the continuity of glass network, and leads to the decrease of the softening temperature Tf of the samples and the increasing trend of crystallization. And that deduces corresponding rise of densification, dielectric constant, dielectric loss of the low temperature co-fired ceramic （LTCC） materials and the decrease of its thermal conductivity. By contrast, the borosilicate glass/A1203 composites with 1.5% （mass fraction） alkali oxides sintered at 875 ℃ for 30 rain exhibit better properties of a bulk density of 2.79 g/cm3, a porosity of 0.48%, a 2 value of 2.28 W/（m.K）, a er value of 7.82 and a tand value of 9.1 × 10-4 （measured at 10 MHz）.展开更多
The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approach...The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.展开更多
A new and upcoming application is the use of 60 GHz antennas for high date rate point-to-point connections to serve Gigabit(Gi-Fi)w ireless communications.The design of M illimeter w ave(M m W)antennas has to cope w i...A new and upcoming application is the use of 60 GHz antennas for high date rate point-to-point connections to serve Gigabit(Gi-Fi)w ireless communications.The design of M illimeter w ave(M m W)antennas has to cope w ith the unadorned influences of manufacturing tolerances and losses at 60 GHz.In this paper,the concept of Substrate Integrated Waveguide(SIW)and Exponentially Tapered Slot(ETS)antenna w ere used together to design a high gain,efficient planar dielectric loaded antenna for M m W Gi-Fi w ireless communications at 60 GHz.The SIW is used to feed the antenna and a dielectric is utilized in front of the antenna to increase the gain.The dielectric loaded ETS antenna and compact SIW feed w ere fabricated on a single substrate,resulting in low cost and easy fabrication.The antenna w ith elliptical shaped dielectric loaded w as fabricated using printed circuit board process.The measured gain of the single element antenna is 10.2 dB,w hile the radiation efficiency of 96.84%is obtained at 60 GHz.The Y-junction SIW pow er divider is used to form a 1×4 array structure.M easured gain of the 1×4 array antenna is 13.3 dB,w hile the measured radiation pattern and gain are almost constant w ithin the w ide bandw idth of the antenna.展开更多
Schematic illustration of the PEO of the carbon steel in 8 g·L^-1 NaAlO2+2 g·L^-1 NaH 2PO4:(a)the sample before the application of anodic current,(b)the moment after the application of anodic current,(c)the ...Schematic illustration of the PEO of the carbon steel in 8 g·L^-1 NaAlO2+2 g·L^-1 NaH 2PO4:(a)the sample before the application of anodic current,(b)the moment after the application of anodic current,(c)the deposition of an aluminum phosphates or AAP layer on the steel surface,(d)the initiation of plasma discharges through the breakdown of the dielectric layer,(e)stable discharges at later stage of PEO.展开更多
The purpose of this paper is to reduce the error when measuring high dielectric constant materials.In this paper,the reason why the error introduced is analyzed firstly.Then,with HFSS,the method of choosing the size o...The purpose of this paper is to reduce the error when measuring high dielectric constant materials.In this paper,the reason why the error introduced is analyzed firstly.Then,with HFSS,the method of choosing the size of cavity and the dimension of dielectric materials is proposed.And several error correction curves are provided for measuring high dielectric constant materials.Finally,the experiment is conducted to validate the feasibility of our analysis.展开更多
The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show...The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show that the thermodynamic stability of Crdoped Fe_3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe_3C, Fe_(11)CrC_4(g), and Fe_(11)CrC_4(s) are respectively 21.36 μB/cell, 16.92 μB/cell, and 17.62 μB/cell, and in Fe_(11)CrC4(g) and Fe_(11)CrC_4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe_(11)Cr C_4(s)>Cr_3C>Fe_(11)Cr C_4(g)>Fe_3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.展开更多
The structural and electrical properties of lead free Srx-xLax（Tio.sFeo.5）O3 （SLTFO） prepared by standard solid state reaction technique were studied. The X-ray diffraction analysis confirmed the formation of a si...The structural and electrical properties of lead free Srx-xLax（Tio.sFeo.5）O3 （SLTFO） prepared by standard solid state reaction technique were studied. The X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The compositional dependence of lattice constant, density and microstructural studies show that they vary significantly with La3＋ content. When measured at 10 kHz, all the compositions of SLTFO at room temperature exhibit a high permittivity （about 104） and low dielectric loss （about 10-3）. SLTFO also display minimum dielectric loss within the lower and higher limits of frequency, indicating that the samples are of good quality. It is concluded from the calculated ac conductivity that the conduction is due to mixed polarons hopping. The complex impedance plot exhibits a tendency of forming a single semicircular arc for all compositions, which implies a dominance of grain boundary resistance on the impedance. Impedance parameters were determined by fitting the experimental data with Cole-Cole empirical formula. The results of the present experiment indicate that the lead free SLTFO materials with higher permittivity and lower dielectric loss have possible practical applications.展开更多
In this paper, a new numerical method-Kuhn algorithm with contour integral-is intrroduced and used to calculate the complex dielectric permittivities of materials from the short-circuitedwaveguide measurements. Some n...In this paper, a new numerical method-Kuhn algorithm with contour integral-is intrroduced and used to calculate the complex dielectric permittivities of materials from the short-circuitedwaveguide measurements. Some numerical results are given to verify the validity and efficiency ofthe new numerical method and the complex dielectric permittivities of materials calculated by thenew numerical method are quite identical with the results given by other works.展开更多
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Student Training Program for Innovation and Entrepreneurship of Hangzhou Institute for Advanced Study,UCAS(CXCY20230305)Chinese Academy of Sciences Key Project(ZDRW-CN-2021-3-1-18)。
文摘Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.
基金Project(2010GXNSFA013029) supported by the Natural Science Foundation of Guangxi Province,ChinaProject(101059529) supported by National Undergraduate Innovation Program of the Ministry of Education of China
文摘The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.
基金Projects(61574109,61204092)supported by the National Natural Science Foundation of China
文摘The effects of low-κ and high-κ spacer were investigated on the novel tunnel dielectric based tunnel field-effect transistor(TD-FET) mainly based upon ultra-thin dielectric direct tunneling mechanism. Drive currents consist of direct tunneling current and band-to-band tunneling(BTBT) current. Meanwhile, tunneling position of the TD-FET differs from conventional tunnel-FET in which the electron and hole tunneling occur at intermediate rather than surface in channel(or source-channel junction under gate dielectric). The 2-D nature of TD-FET current flow is also discussed that the on-current is degraded with an increase in the spacer width. BTBT current will not begin to play part in tunneling current until gate voltage is 0.2 V. We clearly identify the influence of the tunneling dielectric layer and spacer electrostatic field on the device characteristics by numerical simulations. The inserted Si_3N_4 tunnel layer between P+ region and N+ region can significantly shorten the direct and band-to-band tunneling path, so a reduced subthreshold slope(Ss) and a high on-current can be achieved. Above all the ambipolar current is effectively suppressed, thus reducing off-current. TD-FET demonstrates excellent performance for low-power applications.
基金Project(2007AA03Z0455) supported by the National High-Technology Research and Development Program of ChinaProject(BE2009168) supported by the Natural Science Foundation of Jiangsu Province in ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institution,China
文摘The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of B203 causes the increase of the contents of [BO3], [BO4] and [SiO4], which deduces the increase of CaB204 and a-SiO2 and the decrease of CaSiO3 correspondingly. No new phase is observed throughout the entire experiments. A bulk density of 2.54 g/cm3, a thermal expansion coefficient value of 11.95× 10-6 ℃-1 （20-500℃）, a dielectric constant er value of 6.42 and a dielectric loss tanδ value of 0.000 9 （measured at 9.7 GHz） are obtained for CBS glass ceramics containing 35%-B203 （mass fraction） sintered at 850 ℃ for 15 min.
基金Project(50872001) supported by the National Natural Science Foundation of ChinaProjects(KJ2007B132, KJ2009A006Z) supported by the Scientific Research Foundation of Education Department of Anhui Province, ChinaProject(XJ200907) supported by the Foundation of Construction of Quality Project of Anhui University, China
文摘The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-doped TiO2-based varistor ceramics were fabricated by sintering at 1 250 ℃ for 0.5-5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cma decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 1l5 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0-3.0 h considering both nonlinear electrical behavior and dielectric properties.
基金Project(2007AA03Z0455) supported by the National High Technology Research and Development Program of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institution, China
文摘The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.
基金Project(2013JSJJ002)supported by the Faculty Research Fund of Central South University,China
文摘Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.
文摘Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green＇s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green＇s function can be divided into two parts： primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.
基金Project(2007AA03Z0455) supported by the National High Technology Research and Development Program of ChinaProject(BE2010194) supported by Science&Technology Pillar Program of Jiangsu Province, China+1 种基金Project(KF201103) supported by the State Key Laboratory of New Ceramic and Fine Processing, Tsinghua University, ChinaProject supported by the Priority Academic Development of Jiangsu Higher Education Institutions, China
文摘CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.
基金Project(202045007) supported by the Start-up Funds for Outstanding Talents in Central South University,China。
文摘Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.
基金Project(6140863020216JW30001)supported by the General Armaments Department Pre-research Fund,China。
文摘The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was significantly reduced under nano-gap conditions and the optimal discharge voltage was 2 kV.Then,the anodic bonding and dielectric barrier discharge activated bonding were performed in comparison experiments,and the bonding strength was characterized by tensile failure test.The results showed that the bonding strength was higher under the nano-gap dielectric barrier discharge.This process completed 110°C ultra-low temperature anodic bonding and the bonding strength reached 2 MPa.Finally,the mechanism of promoting bonding after activation is also discussed.
基金Project(2007AA03Z0455) supported by the National High Technology Research and Development Program ("863" Program) of ChinaProject(BE2010194) supported by Science & Technology Pillar Program of Jiangsu in China+3 种基金Project(BE2009168) supported by Science & Technology Pillar Program of Jiangsu in ChinaProject supported by the Priority Academic Program Development (PAPD) of Jiangsu Higher Education InstitutionsProject(KF201103) supported by State Key Laboratory of New Ceramic and Fine Processing Tsinghua UniversityProject(CXZZ12_0415) supported by Innovation Foundation for Graduate Students of Jiangsu Province,China
文摘The effects of alkali oxides （Na2O and K2O addition on both the sintering behavior and dielectric properties of Ca-AI-B-Si-O glass/Al2O3 composites were investigated by Fourier transform infrared spectroscopy （FTIR）, differential scanning calorimeter （DSC）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of alkali oxides in the glass causes the decrease of [SiO4], which results in the decrease of the continuity of glass network, and leads to the decrease of the softening temperature Tf of the samples and the increasing trend of crystallization. And that deduces corresponding rise of densification, dielectric constant, dielectric loss of the low temperature co-fired ceramic （LTCC） materials and the decrease of its thermal conductivity. By contrast, the borosilicate glass/A1203 composites with 1.5% （mass fraction） alkali oxides sintered at 875 ℃ for 30 rain exhibit better properties of a bulk density of 2.79 g/cm3, a porosity of 0.48%, a 2 value of 2.28 W/（m.K）, a er value of 7.82 and a tand value of 9.1 × 10-4 （measured at 10 MHz）.
文摘The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.
基金the DRDO,Government of India for providing financial patronage in executing this research work
文摘A new and upcoming application is the use of 60 GHz antennas for high date rate point-to-point connections to serve Gigabit(Gi-Fi)w ireless communications.The design of M illimeter w ave(M m W)antennas has to cope w ith the unadorned influences of manufacturing tolerances and losses at 60 GHz.In this paper,the concept of Substrate Integrated Waveguide(SIW)and Exponentially Tapered Slot(ETS)antenna w ere used together to design a high gain,efficient planar dielectric loaded antenna for M m W Gi-Fi w ireless communications at 60 GHz.The SIW is used to feed the antenna and a dielectric is utilized in front of the antenna to increase the gain.The dielectric loaded ETS antenna and compact SIW feed w ere fabricated on a single substrate,resulting in low cost and easy fabrication.The antenna w ith elliptical shaped dielectric loaded w as fabricated using printed circuit board process.The measured gain of the single element antenna is 10.2 dB,w hile the radiation efficiency of 96.84%is obtained at 60 GHz.The Y-junction SIW pow er divider is used to form a 1×4 array structure.M easured gain of the 1×4 array antenna is 13.3 dB,w hile the measured radiation pattern and gain are almost constant w ithin the w ide bandw idth of the antenna.
文摘Schematic illustration of the PEO of the carbon steel in 8 g·L^-1 NaAlO2+2 g·L^-1 NaH 2PO4:(a)the sample before the application of anodic current,(b)the moment after the application of anodic current,(c)the deposition of an aluminum phosphates or AAP layer on the steel surface,(d)the initiation of plasma discharges through the breakdown of the dielectric layer,(e)stable discharges at later stage of PEO.
文摘The purpose of this paper is to reduce the error when measuring high dielectric constant materials.In this paper,the reason why the error introduced is analyzed firstly.Then,with HFSS,the method of choosing the size of cavity and the dimension of dielectric materials is proposed.And several error correction curves are provided for measuring high dielectric constant materials.Finally,the experiment is conducted to validate the feasibility of our analysis.
基金Project(51174252)supported by the Joint Funds of the National Natural Science Foundation of China
文摘The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show that the thermodynamic stability of Crdoped Fe_3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe_3C, Fe_(11)CrC_4(g), and Fe_(11)CrC_4(s) are respectively 21.36 μB/cell, 16.92 μB/cell, and 17.62 μB/cell, and in Fe_(11)CrC4(g) and Fe_(11)CrC_4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe_(11)Cr C_4(s)>Cr_3C>Fe_(11)Cr C_4(g)>Fe_3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.
基金Project supported by CASR of Bangladesh University of Engineering and Technology(BUET)
文摘The structural and electrical properties of lead free Srx-xLax（Tio.sFeo.5）O3 （SLTFO） prepared by standard solid state reaction technique were studied. The X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The compositional dependence of lattice constant, density and microstructural studies show that they vary significantly with La3＋ content. When measured at 10 kHz, all the compositions of SLTFO at room temperature exhibit a high permittivity （about 104） and low dielectric loss （about 10-3）. SLTFO also display minimum dielectric loss within the lower and higher limits of frequency, indicating that the samples are of good quality. It is concluded from the calculated ac conductivity that the conduction is due to mixed polarons hopping. The complex impedance plot exhibits a tendency of forming a single semicircular arc for all compositions, which implies a dominance of grain boundary resistance on the impedance. Impedance parameters were determined by fitting the experimental data with Cole-Cole empirical formula. The results of the present experiment indicate that the lead free SLTFO materials with higher permittivity and lower dielectric loss have possible practical applications.
文摘In this paper, a new numerical method-Kuhn algorithm with contour integral-is intrroduced and used to calculate the complex dielectric permittivities of materials from the short-circuitedwaveguide measurements. Some numerical results are given to verify the validity and efficiency ofthe new numerical method and the complex dielectric permittivities of materials calculated by thenew numerical method are quite identical with the results given by other works.
