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/℃.

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.

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.

Microwave dielectric properties of CaCu_(3)Ti_(4)O_(12) ceramics:A clue to its intrinsic dielectric response

CaCu_(3)Ti_(4)O_(12)(CCTO)is a potential dielectric material with giant permittivity,good stability over the wide temperature and frequency range.However,the dielectric responses of CCTO-based ceramics are mainly investigated in the frequency of 102-106 Hz,which is far low to clarify the intrinsic dielectric feature.So,microwave dielectric properties have been investigated for the CCTO porous ceramics sintered at low temperature(≤1000°C).Good microwave dielectric properties of permittivityε=62.7,quality factor Qf=3062 GHz and temperature coefficient of the resonant frequencyτf=179 ppm/°C are achieved for the CCTO ceramics sintered at 1000°C,the dielectric loss significantly decreases two orders to 0.002 compared to that of CCTO ceramics sintered at critical temperature of 1020°C confirmed by differential scanning calorimetry(DSC).This clue indicates that giant permittivity and high loss is not intrinsic for CCTO ceramics,but derives from composition segregation,liquid phase and defects associated with internal barrier layer capacitor(IBLC).It suggests that CCTO-based ceramics is a promising microwave dielectric materials with high permittivity.

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.

Influence of(Mg_(1/3)Nb_(2/3))complex substitutions on crystal structures and microwave dielectric properties of Li2TiO3 ceramics with extreme low loss

A systematic investigation of the Li2Ti1-x(Mg_(1/3)Nb_(2/3))xO_(3)(0.1≤x≤0.35)solid solutions synthesized by traditional solid-state reaction method is reported in this work.In the composition range of 0.1≤x≤0.25,a monoclinic rock salt structured solid solution was formed.When x increased to 0.3,a phase transition from monoclinic to cubic phase,along with an order-disorder phase transition,was observed.With x increased from 0.1 to 0.35,the microwave permittivity(εr)and temperature coefficient of resonant frequency(TCF)of the Li2Ti1-x(Mg_(1/3)Nb_(2/3))xO_(3)ceramics decreased linearly from 21.0 to 18.6,+27.1 to-19.4 ppm/℃,respectively.The Li_(2)Ti_(0.75)(Mg_(1/3)Nb_(2/3))0.25O_(3)ceramic sintered at 1170℃shows high performance of microwave dielectric properties with aεr~19.6,a Qf(Q=quality factor=1/dielectric loss;f=resonant frequency)~109,770 GHz(at 7.7 GHz)and a near zero TCF~t 1.2 ppm/℃.Moreover,the burying sintering process can reduce the volatilization of lithium so that the porosity of Li_(2)Ti_(0.75)(Mg_(1/3)Nb_(2/3))0.25O_(3)ceramic was reduced effectively,which made Li_(2)Ti_(0.75)(Mg_(1/3)Nb_(2/3))0.25O_(3)ceramic promising for future applications.Selected area electron diffraction patterns,high-resolution transmission electron microscopy,Raman and far-infrared spectra were employed to study the relation between crystal structure and microwave dielectric properties in detail.

Microstructures and microwave dielectric properties of (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 solid solutions

(Bal-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 (x=0.02,0.04,0.06,0.08,0.1) solid solutions were prepared by the conventional solid-state reaction process.It was found that (Ba1-xSrx)4(Sm0.4Nd0.6)28/3 Ti18O54 ceramics are fully composed of BaSm2Ti4O12 and BaNd2TisO14 phases for all the compositions.The increasing x value (0.02 ≤ x ≤ 0.1) in (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramics can not only obtain high Q ×f value but also effectively enhance the permittivity (εr).The (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramic with x=0.08,sintered at 1440 ℃ for 4 h,shows excellent microwave dielectric properties of permittivity (εr) ≈ 93.19,quality factor (Q × f) ≈ 9770.14 GHz (at 3.415 GHz),and almost near-zero temperature coefficient of resonant frequency (rf)≈ +4.56 ppm/℃.

DEPENDENCE OF MICROWAVE DIELECTRIC PROPERTIES ON STRUCTURAL CHARACTERISTICS OF ILMENITE,TRI-RUTILE AND WOLFRAMITE CERAMICS

Effects of crystal structures on dielectric properties of ATiO_(3)(trigonal ilmenite),ATa_(2)O_(6)(tetragonal tri-rutile)and AWO_(4)(monoclinic wolframite)(A=Ni,Mg,Co)ceramics with A-and B-site oxygen octahedra were investigated at microwave frequencies.The dielectric constant(K) of the specimens was affected by the dielectric polarizabilities of composition and cation bond valence between octahedral cation and oxygen ion per molar volum(V_(m)).The quality factor(Qf)of ATiO_(3)was appreciably larger than those of ATa_(2)O_(6)and AWO_(4)due to the different sharing types of oxygen octahedra.The temperature coe±cient of resonant frequency(TCF)of the specimens was dependent on the octahedral distortion per V_(m).

Enhanced microwave dielectric properties of wolframite structured Zn_(1-x)Cu_(x)WO_(4) ceramics with low sintering temperature

The crystal structure,Raman vibration,chemical bond characteristics,and microwave dielectric properties of Zn_(1-x)Cu_(x)WO_(4)(x=0-0.15)ceramics prepared by a solid-state reaction were investigated by XRD refinement,Raman spectroscopy,P-V-L theory and XPS.According to the P-V-L theory,the properties of the W-O bond are stronger than those of the Zn-O bond,which makes a major contribution to the dielectric properties.The relative permittivity is mainly affected by the average bond ionicity,and the variations in the dielectric loss and tf are mainly attributed to the lattice energy and bond energy.XPS shows that the presence of Cut could produce oxygen vacancy defects,increasing the dielectric loss.Additionally,Raman spectra show that the increasing molecular polarizability causes the Raman shift to move to a low wavenumber,and the changes in Raman intensity and FWHM lead to a decrease in the degree of short-range ordering.Particularly,Zn_(0.97)Cu_(0.03)WO_(4) ceramics sintered at 925℃ showed satisfactory properties(εr=14.20,tanδ=1.473×10^(-4) at 9.087 GHz,and tf=-40 ppm/℃),which can potentially be applied to LTCC technology and indicate that Cu substitution can not only reduce the sintering temperature,but also optimize the dielectric properties.

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.

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,

INFLUENCE OF n ON STRUCTURE AND MICROWAVE DIELECTRIC PROPERTIES OF SOME A_(n)B_(n-1)O_(3n)PEROVSKITES

Two series of B-site deficient perovskites Ba_(5+m)Ti_(m)Nb_(4)O_(15+3m)(m=1,2,3)and Sr_(3+m)LaTi_(m)Nb_(3)O_(12+3m)(m=0,1,2)with the general formula A_(n)B_(n-1)O_(3n)(n=4-8;A=Ba,Sr,La;B=Nb,Ti)have been synthesized,and their structure and microwave dielectric properties have been investigated.The effects of n(number of octahedra layers within a perovskite blocks)on structure and properties are investigated.The values of dielectric constantε_(r)and temperature coe±cient of resonant frequencyτ_(f)gradually increase,but quality factors Q×f values significantly decreases as the values of n increase.

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).

Sintering characteristics and microwave dielectric properties of 0.5Ca_(0.6)La_(0.267)TiO_3-0.5Ca(Mg_(1/3)Nb_(2/3))O_3 ceramics prepared by reaction-sintering process

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.