Study on Microwave Dielectric Property of Carbon Black and Short Carbon Fibers

Carbon black and carbon fibers of different lengths were introduced in different matrices at different ratios to explore their microwave dielectric properties under 8.2 GHz-12.4 GHz. It is found that the actual dielectric constants of the samples containing carbon black are in a two-order function of the contents of carbon black （ε＇, ε＂=Av2＋Bv＋C） and the complex dielectric constants show an obvious frequency response. Of the added fibers of different lengths, the 4 mm-long one could well disperse in the matrices having not only good frequency response, but also larger real parts, imaginary parts and loss values. The imaginary parts and the loss values （tanδ）of the samples with 4 mm-long carbon fibers added increase linearly with the contents of fiber increasing. So it is practicable to adjust the dielectric parameters of the material in a wide range by changing the added amount of carbon black, and the carbon fiber or altering the lengths of the carbon fiber added.

Low-temperature sintering and microwave dielectric properties of Li_2MgTi_3O_8 ceramics doped with BaCu(B_2O_5)

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.

Microstructure and microwave dielectric properties of ZnO-B_2O_3 added (Ca_(0.254)Li_(0.19)Sm_(0.14))TiO_3 ceramics

The effects of ZnO-B2O3 （ZB2） on the sintering behavior and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics were investigated. The densities of the specimens reached the maximum value by adding 3 wt.% ZB2 and then decreased. The sintering temperature of the specimens was lowered from 1300 to 1100℃ without degradation of the microwave dielectric properties. The （Ca0.254Li0.19Sm0.14）TiO3＋ 3 wt.% ZB2 sintered at 1100℃ for 3 h showed good microwave dielectric properties, εr= 108.2, Qf= 6545 GHz, and rf= 6.5 ppm/℃, respectively, indicating that ZB2 was an effective sintering aid to improve the densification and microwave dielectric properties of （Ca0.254Li0.19Sm0.14）TiO3 ceramics.

Influence of CaxSr1-x(0≤x≤1)Substitution for Zn on Microwave Dielectric Properties of Li2ZnTi3O8 Ceramic as Temperature Stable Materials

A temperature stable Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics were fabricated using a conventional solid-state route sintered at 1100℃for 4 h.The XRD results indicate that the main phase Li2ZnTi3O8 and secondary phase including SrxCa1-xTiO3(0≤x≤1)solid solution and TiO2 co-exist in composite and form a stable composite system when the(CaxSr1-x)(0≤x≤1)substitutes for Zn of Li2ZnTi3O8 ceramic.As x is increased from 0 to 1,the relative permittivity(εr)increases from 26.65 to 27.12,and the quality factor(Q×f)increases from 63300 to 66600 GHz.With the increased of x,the temperature coefficient of resonant frequency(τf)increases from 0.27 to 8.23 ppm/℃,and then decreases to 3.51 ppm/℃.On the whole,the Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics show excellent comprehensive properties of middleεr=25-27,higher Q×f≥60000 GHz andτf≤±8.5 ppm/℃.

Dielectric Properties and Microwave Heating of Molybdenite Concentrate at 2.45 GHz Frequency

Dielectric properties were measured using cavity perturbation method. The temperature rising behaviors of molybdenite concentrate were investigated in the field of microwave. This process was conducted to show the microwave absorption properties of molybdenite concentrate and the feasibility of microwave roasting molybdenite concentrate to prepare high purity MOO3. The dielectric constant,dielectric loss,and loss tangent increase from 3. 51 to 5. 04,0. 22 to 0. 51 and 0. 065 to 0. 102 respectively. They are proportional to the apparent density of molybdenite concentrate in the range of 0. 9-1. 4 g/cm3. The results show that the molybdenite concentrate has good microwave absorption capacity in the conventional density range. The temperature rising curves show that the apparent heating rate of the molybdenite concentrate increases with the increase in microwave power and decreases with the increase in the sample mass and thickness. The temperature of concentrate sample of 100 g reaches approximately 800 ℃ after 5 min of microwave treatment at 0. 5 kW of power. Our findings show that it is feasible to prepare high-purity MOO3from molybdenite concentrate by microwave roasting.

Microstructures and Microwave Dielectric Properties of La-Substituted Ba(Mg_1/3Nb_(2/3))O_3 Ceramics

La substituted Ba(Mg_ 1/3Nb_ 2/3)O_3 ceramics was expected to enhance the 1∶2 ordering degree of B-site ions due to the existence of vacancies that promote cation movement and result in improvement of the Q_f value. The relation between the microstructure and microwave dielectric properties of Ba_ 1-xLa_ 2x/3(Mg_ 1/3Nb_ 2/3)O_3 ceramics was investigated. La substituted Ba(Mg_ 1/3Nb_ 2/3)O_3 ceramics can improve the sinterability of specimens. Both 1:2 ordering degree and grain size increase as A-site vacancies increase. This can be explained by the existence of vacancies that promote cation movement. The Q_f value increase with small La content, then decrease rapidly. The highest Q_f value achieved in this investigation is about 55000 GHz for Ba_ 0.995La_ 0.01/3(Mg_ 1/3Nb_ 2/3)O_3. The improvement of Q_f value with A-site vacancies is related to the increase of the degree of B-site ordering and grain size of the specimen.

Effect of La ^(3+) on Microwave Dielectric Properties of (Pb_ (0.45)Ca_ (0.55))(Fe_(0.50Nb_ (0.5))O_3 Ceramics

In this work, microwave dielectric properties of A-site substitution by La 3+ in (Pb_ 0.45Ca_ 0.55)(Fe_ 0.5Nb_ 0.5)O_3 system were investigated. Microwave dielectric properties of A-site charge unbalance substitution of [(Pb_ 0.45Ca_ 0.55)_ 1-xLa_x](Fe_ 0.5Nb_ 0.5)O 3+ (P45CLFN) were improved because the solid solution of small amount of surplus La 3+ with (Pb,Ca) 2+ could eliminate oxygen vacancies, and the formation of secondary phase(pyrochlore) was also caused by surplus La 3+. The decreasing of dielectric constant with the increase of La 3+ content is due to the formation of pyrochlore. The grain size is changed slightly and Q_f values(7000～7300 GHz) are almost unchanged at x=0.02～0.10, but the temperature coefficient of resonant frequency (TCF) are increased and changed from negative to positive. TCF is zero at x=0075 with Q_f=7267 GHz and K=89. TCF of all specimens are within ±5×10 -6 ℃ -1.

Structure and Dielectric Properties of ZnO and Nb_2O_5 Doped BaO-TiO_2 System Microwave Ceramics

The microwave dielectric properties and microstructure of BaTi4.3ZnyO9.6＋y ＋0.02 mol% SnO2＋0.01 mol% MnCO3＋x mol% Nb2O5（x=0-0.05, y=0-0.08） system ceramics were studied as a function of the amount of ZnO and Nb2O5 doped. Addition of （y=0-0.05） ZnO and （x=0-0.025） Nb2O5 enhanced the reactivity and decreased the sintering temperature effectively. It also increased the dielectric constant ε r and quality factor Q（=1/tan 8） of the system due to the substitution of Ti^4＋ ions with incorporating Zn^2＋and Nb^5＋ ions, which was analyzed by the reaction ZnO＋Nb2O5＋ 3 TiTxTi →ZnTi＋ 2NbTi＋3TiO2. When the system doped with （y=0.05） ZnO and （x=0.025） Nb205 were sintered at 1 160 ℃ for 6 h, the εr. Qf0 value and rfwere 36.5, 42 000 GHz, and＋1.8 ppm/℃, respectively, at 5 GHz.

Low-Temperature Sintering and Microwave DielectricProperties of Ba_2Ti_3Nb_4O_(18) Ceramics

The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO （ 〈1 wt%） considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 （ 〈3.5 wt%） remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.Ba2Ti3Nb4O18 ceramics sintered at 1 050 ℃ for 4 h with the addition of 1.0 wt% CuO and 3.5 wt% H3BO3 exhibited good microwave dielectric properties：er=33.74,Q？f=13 812 GHz,and tf=-5.35 ppm/°C at about 5.0 GHz.

Dielectric behaviors at microwave frequencies and Mossbauer effects of chalcedony, agate, and zultanite

In this study, dielectric properties within 8-12 GHz microwave frequencies, inductively coupled plasma-atomic emis- sion spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57Fe Mossbauer spectroscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm-1 to 4000 cm-1 range, ε＇ values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, eI and e~ values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57Fe Mossbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanoparticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.

Enhanced thermal conductivity and microwave dielectric properties by mesostructural design of multiphase nanocomposite

Next-generation packaging materials are expected to have higher thermal conductivity,because the heat accumulated in high-performance electronic equipment should be removed to increase the service life of the equipment.At the same time,the dielectric loss of the material needs to be reduced to lessen signal delay and attenuation,especially for the applications under high frequency.In this work,we introduce nano-silicon carbide(SiC)and carbon nanotubes(CNTs)into the polystyrene(PS)and poly(methyl methacrylate)(PMMA)blends system.The design of two-way migration at the interface of CNTs and SiC nanoparticles is realized through the masterbatch method and processing technology control.As a result,the thermal conductivity is successfully increased up to 75%.Meanwhile,compared to the CNTs single-phase migration system,it effectively reduces the dielectric loss of the nanocomposite and optimizes the electrical insulation.This work has significant practical application value in the design of electronic device substrates and packaging materials,and provides an innovative methodology for the mesostructure design of multiphase nanocomposites.

Effects of La^(3+) on microwave dielectric properties of(Pb_(0.5)Ca_(0.5))(Fe-(0.5)Ta_(0.5))O_3 ceramics

This work investigated the microwave dielectric properties of A-site substitution by rare earth La3＋in（Pb0.5Ca0.5）（Fe0.5Ta0.5）O3（PCFT） system.A single perovskite phase was obtained only when the doping content was 2%.Suitable La3＋ doping improved microwave dielectric performances.Excessive La3＋doping caused the formation of secondary phase,which resulted in the decreasing of permittivity εrand quality factor Qfvalues.Especially,when the doping content is 2%-5%,permittivity εrwas above 75 and Qfvalues were 6 902-7 416 GHz.

Structure and Dielectric Properties of Sb_2O_5-Doped ZrO_2-SnO_2-TiO_2 Microwave Ceramics

The microwave dielectric properties of ZrO2-SnO2-TiO2 （ZST） system ceramics were studied as a function of the amount of Sb2O5 dopant. With the addition of 0-0.5% Sb2O5（molar ratio）, the substitution of Ti4^＋ ions with Sb^5＋ ions decreased the sintering temperature and increased the quality factor Q due to the reduction of oxygen vacancies, When the amount of Sb^5＋ increased further （above 0.5%）, Q was decreased by increasing the electron concentration. When the system doped with 0.5% Sb2O5 was sintered at 1 150℃ for 6 h, the relative dielectric constant ε, Qf0, and the temperature coefficient of resonant frequency （TCF） were 38.46, 44 500 GHz, 20.0×10^-6/℃, respectively, at 6 GHz,

SrGa_(12)O_(19):The first low-ε_(r) Ga-based microwave dielectric ceramic with anomalous positiveτ_(f)

Dielectric ceramics with low permittivity(ε_(r)),high quality factor(Q×f),and near-zero resonant frequency(τ_(f))in the microwave bands are key materials used in fifth/sixth-generation(5G/6G)telecommunication,whileτ_(f) of most low-εr microwave dielectric ceramics is relatively negative.In this work,the first low-εr Ga-based ceramic SrGa_(12_O_(19) with an anomalous positiveτ_(f) was reported,and the causes of the positiveτ_(f),intrinsic polarization,and loss mechanism were systematically studied.X-ray diffraction(XRD)and transmission electron microscopy(TEM)revealed that the SrGa_(12_O_(19) ceramic formed a pure hexagonal magnetoplumbite structure with spinel blocks and rock-salt blocks stacked along the crystallographic c-axis.When sintered at 1430℃,it possessed the optimal microwave dielectric properties of a lowεr of 14.46,high Q×f of 64,705 GHz,and exceptional positiveτ_(f) of+55.7 ppm/℃,along with a low linear thermal expansion coefficient(αL)of 11.617 ppm/℃.The large positive deviation betweenεr andεr(C–M)of 45.31%resulted from the rattling effect of atoms in the rock-salt block.The unique positiveτ_(f)(+55.7 ppm/℃)was governed by the rattling effect,resulting in a positiveταm(the temperature coefficient of ion polarizability)of 8.489 ppm/℃ and a large negative temperature coefficient of permittivity(τε)of−132.864 ppm/℃.Phillips–Vechten–Levine(P–V–L)chemical bond theory revealed greater contributions of the spinel block to bond ionicity(fi,52.95%),permittivity(ε,55.15%),bond energy(E,56.87%),and lattice energy(U,74.88%)than those of the rock-salt block.The intrinsic dielectric properties were analyzed using infrared(IR)reflectivity spectra.The favorable performance of the SrGa_(12)O_(19) ceramic indicated that it is a novelτ_(f) compensator.This selection of compounds with different structural layer combinations provides a new idea for exploring excellent microwave dielectric ceramics.

Low-permittivity LiLn(PO_(3))_(4)(Ln=La,Sm,Eu)dielectric ceramics for microwave/millimeter-wave communication

The development of dielectric materials with low permittivity and low loss is a great challenge in wireless communication.In this study,LiLn(PO_(3))_(4)(Ln=La,Sm,Eu)ceramic systems were successfully prepared using the traditional solid-state method.X-ray diffraction analysis indicated that the LiLn(PO_(3))_(4)ceramics crystallized in a monoclinic structure when sintered at 850–940℃.The characteristic peak shifted to higher angles with variations in the Ln element,which was ascribed to a reduction in the cell volume.Further analysis by structure refinement revealed that the reduction in the cell volume resulted from the decrease in chemical bond lengths and the compression of[LiO_(4)]and[PO_(4)]tetrahedra.Remarkably,the LiLn(PO_(3))_(4)ceramic system displayed exceptional performance at low sintering temperatures(910–925℃),including a high quality factor(Q·f)of 41,607–75,968 GHz,low temperature coefficient of resonant frequency(τ_(f))ranging from−19.64 to−47.49 ppm/℃,low permittivity(ε_(r))between 5.04 and 5.26,and low density(3.04–3.26 g/cm^(3)).The application of Phillips–van Vechten–Levine(P–V–L)theory revealed that the increased Q·f value of the LiLn(PO_(3))_(4)systems can be attributed to the enhanced packing fraction,bond covalency,and lattice energy,and the stability of τ_(f) was associated with the increase in the bond energy.Furthermore,a prototype microstrip patch antenna using LiEu(PO_(3))_(4) ceramics was fabricated.The measurement results demonstrated excellent antenna performance with a bandwidth of 360 MHz and a peak gain of 5.11 dB at a central frequency of 5.08 GHz.Therefore,low-εr LiLn(PO_(3))_(4)ceramic systems are promising candidates for microwave/millimeter-wave communication.

Effects of(Mg_(1/3)Sb_(2/3))^(4+)substitution on the structure and microwave dielectric properties of Ce_(2)Zr_(3)(MoO_(4))_(9) ceramics

Ce2[Zr_(1-x)(Mg_(1/3)Sb_(2/3))_(x)]_(3)(MoO_(4))_(9)(0.02≤x≤0.10)ceramics were prepared by the traditional solid-state method.A single phase,belonging to the space group of R3c,was detected by using X-ray diffraction at the sintering temperatures ranging from 700 to 850℃.The microstructures of samples were examined by applying scanning electron microscopy(SEM).The crystal structure refinement of these samples was investigated in detail by performing the Rietveld refinement method.The intrinsic properties were calculated and explored via far-infrared reflectivity spectroscopy.The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by Phillips-van Vechten-Levine(P-V-L)theory.Ce_(2)[Zr_(0.94)(Mg_(1/3)Sb_(2/3))_(0.06)]_(3)(Mo0_(4))_(9)ceramics with excellent dielectric properties were sintered at 725℃for 6 h(εr=10.37,Q×f=71,748 GHz,andτf=-13.6 ppm/℃,εr is the dielectric constant,τf is the quality factor,and rf is the temperature coefficient of resonant frequency).

Synthesis and Characterization of Cubic Zinc Titanate Doped with Lithium

Cubic （Zn,Li）TiO3 powders were synthesized through a modified sol-gel route including the Pechini process via a three-step heat treatment.The as-synthesized （Zn,Li）TiO3 could be stable up to 1000 °C.The dielectric constant and dielectric loss tangent of all the synthesized （Zn,Li）TiO3 samples at different measurement frequencies showed the similar tendency.At the same frequency,the dielectric constant and the dielectric loss tangent of （Zn,Li）TiO3 samples decreased and increased,respectively,with the lithium doping content increase.The as-prepared （Zn,Li）TiO3 showed improved microwave dielectric properties,and its maximum value of quality factor could reach 34000 GHz.

Low-temperature sintering and microwave dielectric properties of CaMg1−xLi2xSi2O6(x=0−0.3)ceramics

In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi2O6 as the main phase. The second phases were CaSiO3 always existing and Li2SiO3 occurring at substitution content x > 0.05. Li+ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (εr) were investigated. The quality factor (Q × f) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τf) was influenced by MgO6 octahedral distortion and bond valence. Excellent dielectric properties of the CaMg1−xLi2xSi2O6 ceramic was exhibited at x = 0.05 with εr = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τf = −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.

Effect of Sb-site nonstoichiometry on the structure and microwave dielectric properties of Li_(3)Mg_(2)Sb_(1-x)O_(6) ceramics

The non-stoichiometric Li_(3)Mg_(2)Sb_(1-x)O_(6)(0.05≤x≤0.125)compounds have been prepared via the mixed oxide method.The influences of Sb nonstoichiometry on the sintering behavior,microstructure,phase composition along with microwave dielectric performances for Li_(3)Mg_(2)Sb_(1-x)O_(6) ceramics were studied.Combined with X-ray diffraction(XRD)and Raman spectra,it was confirmed that phase composition could not be affected by the Sb nonstoichiometry and almost pure phase Li_(3)Mg_(2)SbO_(6) was formed in all compositions.Appropriate Sb-deficiency in Li_(3)Mg_(2)SbO_(6) not only lowered its sintering temperature but also remarkably improved its Q×f value.In particular,non-stoichiometric Li_(3)Mg_(2)Sb_(0.9)O_(6) ceramics sintered at 1250℃/5 h owned seldom low dielectric constant ε_(r)=10.8,near-zero resonant frequency temperature coefficient τ_(f)=-8.0 ppm/℃,and high quality factor Q×f=86,300 GHz(at 10.4 GHz).This study provides an alternative approach to ameliorate its dielectric performances for Li_(3)Mg_(2)SbO_(6)-based compounds through defect-engineering.

Microwave dielectric high-entropy ceramic Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4) with stable temperature coefficient for low-temperature cofired ceramic technologies

High-entropy ceramics are new single-phase materials with at least four cation or anion types.Their large configurational entropy is believed to enhance the simultaneous solubility of many components,which can be used to optimize certain properties.In this work,a high-entropy oxide,Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4)(LRG)was explored as a microwave dielectric ceramic for lowtemperature cofired ceramic technologies.The LRG high-entropy ceramic with an olivine structure formed in the sintering temperature range of 1020-1100℃.The minimal distortion(5×10^(-4))of the[RO_(6)]octahedron led to a stable temperature coefficient of resonant frequency(τf)of-5.3 to-2.9 ppm/℃.Optimal microwave dielectric properties were achieved in the high-entropy ceramics at 1080℃ for 4 h with a relative density of 94.9%,a relative permittivity(ε_(r))of 7.2,and a quality factor(Q×f)of 29000 GHz(at15.3 GHz).For low-temperature cofired ceramic technology applications,the sintering temperature of the LRG high-entropy ceramic was reduced to 900℃ by the addition of 3 wt%H_(3)BO_(3),which exhibited outstanding microwave dielectric properties(ε_(r)=7.6,Q×f=11700 GHz,and τ_(f)=-7.4 ppm/℃)and a good chemical compatibility with silver.