Search

A series of new Li 2 SiO 3 +4 wt% Al 2 O 3 -xK 2 O–B 2 O 3 –SiO 2 (x = 1–4 wt%) LTCC materials were prepared by standard traditional solid-state method and their bulk density, microstructure and crystalline phase composition were shown in detail. The sintering behavior, heat conduction and thermal expansion of the samples were all thoroughly studied. And their microwave dielectric properties were also demonstrated. The bulk density of the samples was enhanced with the addition of 3 wt% KBS glass, and the sintering temperature was reduced from 1020 °C to 900 °C. Meanwhile, the thermal diffusivity of the samples was determined using the LFA447 laser flash apparatus and the specific heat was calculated, according to the results of thermal diffusivity and specific heat, all samples possessed high thermal conductivity ranging from 5.5 ± 0.02 W/mK to 8.6 ± 0.08 W/mK. Furthermore, the attractive flexural strength and average coefficient of thermal expansion reach to 270 MPa and 15.7 × 10−6/K (at 100 °C), respectively. The reduction of the sintering temperature is attributed to the addition of KBS glass which reduces the crystallization activation energy of the samples. Besides, increasing bulk density can substantially reduce pores in the grain boundary, which has great effects on phonon scattering, improving the thermal conductivity. [ABSTRACT FROM AUTHOR]

In this work, a novel material candidate, containing Li2SiO3 (LS) ceramic and CaO–B2O3–SiO2 (CBS) glass for low-temperature co-fired ceramics (LTCC) application was developed via the traditional solid-state reaction process. It is shown that the addition of CBS glass significantly improves the sintering characteristics of LS + CBS glass–ceramic systems at low temperatures by lowering the sintering activation energy. Phase coexistence of the main crystalline phase of Li2SiO3 and minor trace of Li2Si2O5 phase was confirmed. The LS + 6 wt% CBS system presents excellent properties, sintered at 875 °C for 2 h: a εr value of 6.28, a Q × f value about 3527 GHz, a flexural strength 272 MPa, a CTE value of 7.35 × 10–6/°C, and a thermal conductivity λ > 10 W/m/K, denoting its promising future for LTCC substrate application. [ABSTRACT FROM AUTHOR]

The effects of LB glass on the sintering behavior, structure, and dielectric properties for the Ba3.75Nd9.5Ti17.5(Cr0.5Nb0.5)0.5O54 (BNTCN) ceramic were investigated. The results showed that the LB glass, as an effective sintering aid, successfully lowered the sintering temperature of BNTCN ceramic by formation of the liquid phase. Furthermore, the change of the structure and decrease in grain size had influences on the electrical conductivity, thermal stability, and microwave dielectric properties for the BNTCN ceramics doped LB glass. Finally, the excellent microwave dielectric properties with εr = 73.4, Q × f = 5277 GHz, and τf = +7.1 ppm/°C were obtained for samples sintered at 950°C when x = 5, indicating the BNTCN ceramic doped with 5 wt% LB glass is a promoting LTCC material. [ABSTRACT FROM AUTHOR]

For the first time, B2O3–SiO2 (BS) glass-doped Ba5Nb4O15 (BN) ceramics for low-temperature co-fired ceramic (LTCC) applications were facilely synthesized by the conventional solid-phase synthesis strategy. The influences of glass additive content on phase evolution, microstructure, and sintering activation energy were systematically deciphered associated with the microwave dielectric properties of the ceramics. While remaining original phase of Ba5Nb4O15, trace BS additive doping will effectively lessen the sintering temperature from 1350 to 925 °C excluding sacrificing microwave dielectric properties significantly. Optimized dielectric property is achieved via further time modulation: with 0.6 wt.% doping BS glass, Ba5Nb4O15 ceramics sintered at 925 °C for 4 h exhibits best characteristics of εr = 41.2, Q × f = 22,238 GHz, τf = 53.1 ppm/°C. Therefore, Ba5Nb4O15 ceramics doped with BS glass are potential candidates for LTCC. [ABSTRACT FROM AUTHOR]

In this study, the crystal structure, phase composition, Raman spectrum, and microwave dielectric properties of novel Co 0.5 Zr 0.5 TaO 4 ceramics were investigated. Based on the X-ray diffraction, Rietveld refinement analysis and Raman spectroscopy, a coexistence of monoclinic-type and trirutile tetragonal phases was confirmed in the temperature range of 1100–1200 °C. The variations of relative density, growth of grain, and contents of each phase are mainly responsible for the developments of microwave dielectric properties of Co 0.5 Zr 0.5 TaO 4 ceramics. Excellent microwave dielectric properties with a ε r of 20.19, a Q × f about 65125 GHz and a τ f ca. of −39.02 ppm/oC were obtained when sintered at 1150 °C. [ABSTRACT FROM AUTHOR]

In this paper, the BaONd2O3TiO2 (BNT) ceramics are synthesized at low temperature with the assistance of Li2OB2O3SiO2 (LBS) and BaOZnOB2O3 (BZB) glasses. The influences of glasses on the sintering behavior, phase composition, microstructure, activation energy (Ea) on the BNT ceramics are studied in detail. The results show that a new phase, Ba2LiB5O10, is formed from the chemical reaction between LBS and BZB glasses. The sintering temperature of BNT ceramics can be effectively reduced by 450 °C due to the synergetic effect of LBS and BZB glasses and the appearance of Ba2LiB5O10 phase. [ABSTRACT FROM AUTHOR]

The effects of Li2ZnTi3O8 addition on the sintering behavior, phase formation, microstructure and microwave dielectric properties of 0.94MgTiO3–0.06CaTiO3 ceramics have been investigated. These results suggested that Li2ZnTi3O8 addition not only contributes in decreasing the sintering temperature, but also enhances grain growth. A new microwave dielectric ceramic, 0.94MgTiO3–0.06CaTiO3–0.015Li2ZnTi3O8 sintered at 1220 °C had optimal dielectric properties (εr = 20.97, Q × f = 70,832 GHz, τf = 3.45 ppm/°C), which satisfies microwave applications in resonators, filters and antenna substrates. [ABSTRACT FROM AUTHOR]

The LaO-BO-ZnO (LBZ) and VO-CuO (VC) glasses were co-doped to the CaLaTiO (CLT) ceramics as the sintering aids. The effects of LBZ and VC glasses on the low temperature sintering characteristics, phase composition, microstructure, activation energy and dielectric properties of CLT ceramics were investigated systematically. The results show that the synergistic effect of the LBZ and VC co-doped glasses can greatly reduce the sintering temperature of CLT from 1350 to 900 °C with excellent microwave dielectric properties, attributing to the reduction of the activation energy ( Ea) of the CLT with co-doped glasses. Typically, CLT ceramics with 3 wt% LBZ and 1 wt% VC sintered at 900 °C/4 h exhibited good microwave dielectric properties of ε = 98.94, Q × f = 4885 GHz (f = 3.25 GHz) and τ = 305.17 ppm/°C. [ABSTRACT FROM AUTHOR]

Effects of different glass/ceramic weight ratio on the physics and dielectric properties of AlO-BO-SiO (ABS) glass/AlO ceramic composites were investigated. The results show that when glass/ceramic = 50:50 (mass fraction), the composite had the excellent comprehensive properties. Then the lower softening temperature CaO-BO-SiO (CBS) glass was added to the ABS glass as sintering flux on this composite. When the CBS glass content was 2 wt%, the composites showed good properties: ε = 4.98, tanδ = 3.59 × 10 (which was 10 % lower than sample without CBS glass), and the flexural strength was 154.77 MPa (which was 16.2 % higher than the sample without CBS glass). [ABSTRACT FROM AUTHOR]

The present study investigated the effect of sintering temperature on the crystallization behavior of polytetrafluoroethylene (PTFE) polymer in SiO filled PTFE (PTFE/SiO) composites, as well as the dependences of dielectric properties, thermal conductivity, water absorption and density on the sintering temperature of composites. The composites were sintered by hot pressing at temperatures of 350-390 °C. The melting peaks of the sintered composites were recorded by the differential scanning calorimetry (DSC), and heats of melting were calculated from the peak areas in DSC curves, then the crystallinity of PTFE in composites was deduced. The intensities of the crystal diffraction peak for PTFE were observed by X-ray diffraction analysis. Moisture absorption of the composites was measured conforming to IPC-TM-650 2.6.2. Archimedes' principle was used to find out the density of the composites. The dielectric constant and loss tangent of the composites were evaluated at microwave frequency region using strip line resonator method according to IPC-TM-650 2.5.5.5 specification. Thermal conductivity was measured by laser thermal conductivity meter. Morphology of PTFE crystals and dispersion of fillers in the PTFE matrix were studied using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

The effects of SrTiO on the sintering behaviors, phase structures, microstructures and the microwave dielectric properties of CaO-BO-SiO (CBS) glasses/AlO ceramics were investigated in this study. The results show that the SrTiO additions can be well sintered with CBS glasses/AlO ceramics at low temperature, and increase the density and the dielectric constant of the CBS glasses/AlO ceramics. Especially, the temperature coefficient of the resonant frequency τ could be adjusted to zero with SrTiO added. And the sample with 15 wt% SrTiO sintered at 850 °C exhibited promising properties of: ε = 10.13, tanδ = 0.00323, τ = −5.35, and σ ≥ 200 MPa. [ABSTRACT FROM AUTHOR]

KO-BO-SiO (KBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for Ba(Sm, Nd)TiO + 2TiO (x = 2/3 and y = 0.5; BSNTT) ceramics. Effects of KBS doping on sintering behavior, microstructure and microwave dielectric properties of BSNTT ceramic were investigated. The appropriate KBS addition significantly lowered the sintering temperature of BSNTT ceramic with slightly damaging its microwave dielectric properties. The X-ray diffraction results showed that all the well sintered samples exhibited the main phase Ba(Sm,Nd)TiO and a certain amount of BaTiO and TiO secondary phases. Besides, the other secondary phase SmTiO formed when 9 wt% KBS added. Then the scanning electron microscopy micrographs of the optimally well-sintered (1075 °C for 3 h) ceramics showed a dense microstructure. With the increasing content of KBS addition, both the dielectric constant ( ε) and quality factor ( Q × f) value decreased. At last, the good microwave dielectric properties of ε = 68.8, Q × f = 6766 GHz, τ = 28.76 ppm/°C were obtained for BSNTT + 5 wt% KBS ceramic sintered in air at 1075 °C for 3 h. [ABSTRACT FROM AUTHOR]

The effects of ZnO content and sintering temperature on the microstructure, bending strength, coefficient of thermal expansion and dielectric properties of LiO-AlO-SiO glass-ceramic are presented. The prepared LiO-AlO-SiO glass-ceramic could be used for the application of LTCC substrate. Glass powders were produced by conventional melt-quenching technique. The sintering and crystallization behavior of glass powders was explored using scanning electron microscopy, differential thermal and X-ray diffraction analyses. The crystalline phase formation in the calcination of LiO-AlO-SiO samples has shown a major phase of LiOAlO7.5SiO and two minor phases ZrO and CaMgSiO. Increasing ZnO content at the expense of SiO was shown to not only promote the densification and lower the linear shrinkage, but also enhance the bending strength and the coefficient of thermal expansion of the glass-ceramic. The linear shrinkage and density of samples will decrease with the increasing sintering temperature. [ABSTRACT FROM AUTHOR]

The influences of different doping contents of composite additive LaO-BO-ZnO-CaO (LBZC) on the sintering behavior, microstructure and microwave properties of BaSr(NdBi)TiO (BSNBT) microwave ceramics were investigated. With an increasing doping content of LBZC, the sintering temperature gradually decreased. The sintering temperature of BSNBT ceramics was significantly lowered to 880 °C by the addition of 20 wt% LBZC. The scanning electron microscopy photographs showed that the fraction of liquid phase increased as increasing the content of LBZC, resulting in deteriorated microwave properties. According to the X-ray diffraction patterns, the dominant crystal phase of samples transformed from BaNdTiOto the minor phase of BaTiO with 10 wt% LBZC dopant, which was further confirmed by energy dispersive spectrometer. The sample with 15 wt% LBZC sintered at 900 °C exhibited the optimum microwave dielectric properties: ε = 54.9, Q × f = 2949 GHz, and τ = 17.2 ppm/°C. [ABSTRACT FROM AUTHOR]

The effects of x wt% HBO+ 1.0 wt% CuO (x = 1.0-10.0) co-doping on microstructure and microwave dielectric properties of 0.85BaTiO-0.15BaZnTiO (BZT) have been investigated according to the conventional solid-state reaction in this study. The X-Ray Diffraction results showed that the main crystal phase in the sintered ceramics was BaTiO. The addition of HBO-CuO resulted in the liquid phase sintering mechanism, which effectively improved their relative densities and lowered the sintering temperature. As HBO doping amount increased from 1.0 to 10.0 wt%, the relative density and ε displayed a sharp increase at first and then a decline when x = 6.0 wt%. The Q × f value experienced a continuously decrease with the addition of HBO when sintered at sintering temperature. The development in τ was different, increasing persistently with the increase of doping amount at different sintering temperature. The HBO-CuO co-doped 0.85BaTiO9-0.15BaZnTiO ceramics had a low sintering temperature of 1000 °C and a high ε value. Good microwave dielectric properties with values of ε = 35.0, Q × f = 20,700 GHz and τ = 12.0 ppm/°C were obtained in the BZT ceramics with 6.0 wt% HBO and 1.0 wt% CuO sintered at 1000 °C for 2 h. [ABSTRACT FROM AUTHOR]

The microstructure and microwave dielectric characteristics of (BaSr)NdTi(ZnNb)O ceramics solid solutions (0 ≤ x ≤ 2.5) were investigated in this study. X-ray diffraction indicated that only BaNdTiO existed in the sintered samples when x value was lower than 2.0, but subsequently a new phase generated with increasing of x value. The dielectric constant (ε) of the samples increased slightly from 83.4 to 85.2 before falling down and quality factor value (Q × f) declined radically from 10,873 to 1321 GHz at optimum sintering temperature of 1450 °C, as x value increased from 0.0 to 2.5. And the temperature coefficient of resonant frequency (τ) could be adjusted to a minimum value and then rebounded because of the second phase NdNbTiO which also sharply deteriorated the quality factor of the samples. At last, the excellent microwave dielectric properties of the samples with values of ε = 85.2, Q × f = 5989 GHz, τ = +14.9 ppm/°C were obtained as x was 1.0 sintered at 1450 °C for 3 h in air. [ABSTRACT FROM AUTHOR]

The effects of CoO addition on the sintering behavior, phase formation, microstructure and microwave dielectric properties of 0.95MgTiO-0.05CaTiO ceramics have been investigated. The structure and microstructure of the ceramics were investigated using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. These results suggested that CoO addition not only contributes in lowering the sintering temperature but also inhibits the formation of second phase MgTiO in 0.95MgTiO-0.05CaTiO ceramics. Moreover, the decomposition of CoO would inhibit the Ti from being restored to Ti, which had the positive effect on the Q × f value. A fine combination of microwave dielectric properties ( ε = 20.48, Q × f = 76,485 GHz, τ = 2.43 ppm/°C) was achieved for 0.95MgTiO-0.05CaTiO-0.01CoO ceramics sintered at 1300 °C for 4 h, which satisfied microwave applications in resonators, filters and antenna substrates. [ABSTRACT FROM AUTHOR]

The effects of CaO-BO-SiO (CBS) glass addition on the sintering temperature and dielectric properties of LiZnTiO-TiO (LZT) composite ceramics have been investigated. Due to the compensating effect of rutile TiO (τ ≈ +450 ppm/ °C), the temperature coefficient of resonant frequency (τ) for LiZnTiO + 4 wt% TiO with biphasic structure was adjusted to a value near zero. The pure LZT ceramics were usually sintered at high temperature of about 1,160 °C. It was found in our experiment that a small amount of CBS glass additives could effectively lower the sintering temperature of LZT ceramics to 900 °C. With increasing the content of CBS glass, both of dielectric constant (ε) and quality factor (Q × f) value decreased. Typically, the 1 wt% CBS glass added LiZnTiO + 4 wt% TiO ceramic sintered at 900 °C for 4 h exhibited good microwave dielectric properties of ε = 26.9, Q × f = 23,563 GHz and τ = −1.5 ppm/ °C, which made it promising for low temperature co-fired ceramics technology application. [ABSTRACT FROM AUTHOR]

Li 2O-B 2O 3-SiO 2 (LBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for tungsten-bronze-type Ba 4Nd 9.3Ti 18O 54 (BNT) ceramic. The effects of LBS additions on the sintering behaviors, microstructures, and microwave dielectric properties of the BNT ceramic have been investigated, indicating that LBS addition obviously lowered the sintering temperature of the BNT ceramic without damaging its microwave dielectric properties. BNT ceramic doped with 3 wt.% and 4 wt.% LBS addition could be well sintered at 975°C and 950°C for 3 h and had excellent properties: εr = 65.99, Q ×  f = 4943 GHz ( f = 4.4 GHz), τf = 19 ppm/°C, and εr = 64.56, Q ×  f = 4929 GHz ( f = 4.3 GHz), τf = 11 ppm/°C, respectively. [ABSTRACT FROM AUTHOR]

The LTCC CaO-BO-SiO (CBS) ceramics were synthesized via solid-state reaction process without any sintering aid. The effects of different sintering temperatures and BO content on the microwave and mechanical properties were investigated. The results show that the best sintering temperature is around 950 °C and increasing amount of BO promotes the crystallization of CaBO enhancing the flexure strength of the CBS ceramics. However, the dielectric and mechanical properties deteriorated rapidly while the amount of BO exceeded 25 wt.%. The sample with 20.5 wt.% BO sintered at 950 °C had the best properties with ɛ = 6.06; tanδ = 0.0015 (1 MHz) and a high flexure strength σ > 180 MPa. [ABSTRACT FROM AUTHOR]

(1−x)ZrTiO-xZnNbO(x = 0.13-0.53) ceramics doped with 0.7 wt% MnCO were prepared by solid-state reaction and they were all sintered well in air at 1,270 °C. XRD analysis suggested there were a two-phase region for ZrTiO-TiO(x = 0.20-0.33) and a single-phase region for ZrTiO(x = 0.40-0.53) because (ZnNb) preferentially substituted Ti sites, and thereafter Zr sites. The addition of Mn, working as acceptors to receive the electrons left by the lost oxygen, raised the Q × f value dramatically. For 0.7 wt% MnCO doped (1−x)ZrTiO-xZnNbO ceramics, with the increase of x, the ε and the τ dropped from 53.4 to 41.0 and from +95 ppm/°C to −35 ppm/°C respectively, and the Q × f value increased from 26,300 GHz to 48,100 GHz. At last, 0.69ZrTiO-0.31ZnNbO+0.7 wt % MnCO ceramics showed excellent dielectric properties: ε = 45.3, Q × f = 43,300 GHz and τ = −0.5 ppm/°C. Another advantage is that the sintering atmosphere was in air, which is benefit to the commercial application. [ABSTRACT FROM AUTHOR]

The microstructure, sintering and dielectric properties of ZrO-, TiO-doped Ca-Si-B based ceramics prepared by solid-phase process were investigated, and the effects of ZrO, TiO content on these performances were analyzed. The Ca-Si-B based ceramics without additive (ZrO or TiO) showed a high sintering temperature (1,100 °C) and had the dielectric properties: dielectric constant (ε) of 8.38, dielectric loss (tanδ) of 1.51 × 10 at 1 MHz, and volume density of 2.47 g/cm. The addition of ZrO TiO was revealed to lower the sintering temperature of Ca-Si-B based ceramics to 1,000 °C and enhance the sintering and dielectric properties: ρ = 2.61 g/cm, ε = 5.85, tanδ = 1.59 × 10 (1 MHz) with ZrO addition, and ρ = 2.65 g/cm, ε = 6.12, tanδ = 6.4 × 10 (1 MHz) with TiO addition, which are superior to the pure Ca-Si-B. The results show that ZrO, TiO as nucleating agents, are conducive to the precipitation of crystals, thus decrease the sintering temperature and improve the dielectric properties of Ca-Si-B based ceramics. [ABSTRACT FROM AUTHOR]

(ZnMg)SiO powders was prepared by the sol-gel process, and the microstructure and dielectric properties of (ZnMg)SiO microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)SiO with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into ZnSiO lattice, and the solid solution limit of Mg in ZnSiO is about x = 0·1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of ZnSiO ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of ZnSiO. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (ZnMg)SiO dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: ɛ = 6·3, Q × f = 189800 GHz and τ = −63 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the LTCC composite materials containing fused silica and monoclinic zirconia ceramic particles, respectively, which based on the composite matrix composed of the barium borate glassy matrix and α-alumina ceramic particles, were prepared by traditional solid-state preparation process at a sintering temperature of 900°C. Sintering mechanism and physical properties, e.g. dielectric properties and coefficient of thermal expansion (CTE), of the LTCC composite ceramics are investigated and discussed in detail in terms of their mineral phase composition. The results indicate that a barium borate glassy phase can be easily formed from a barium borate compound, which is obtained by the chemical combination of barium hydroxide octahydrate and an aqueous solution of boric acid, at a sintering temperature of 900°C. In turn, the barium borate glassy melts can supply a liquid phase sintering aid for the fabrication of the LTCC composite ceramics with the sintering temperature of 900°C during sintering. The introduction of the α-alumina ceramic particles to the barium borate glassy matrix can improve the sintering behavior whereas the presence of fused silica or monoclinic zirconia particles in the composite ceramics is important to adjust the dielectric, thermal and mechanical properties of the LTCC composite materials. The work may be referenced for the fabrication of multi-layer LTCC structures with tailored physical properties. [Copyright &y& Elsevier]

Abstract: The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO–SiO2–B2O3 ceramic matrix composites with ZrO2 addition. The results indicated that ZrO2 addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO3 and a little SiO2 phase existed at the temperature ranging from 950°C to 1050°C. At 0.5wt% ZrO2, CaO–SiO2–B2O3 ceramic matrix composites sintered at 1000°C possess good dielectric properties: ɛ r =5.85, tan δ =1.59×10−4 (1MHz) and excellent microwave properties: ɛ r =5.52, Q · f =28,487GHz (11.11GHz). The permittivity of Zr-doped CaO–SiO2–B2O3 ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150°C. Moreover, the ZrO2-doped CaO–SiO2–B2O3 ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20Hz to 1MHz. [Copyright &y& Elsevier]

The effects of BiVO and CaTiO additives on the microwave dielectric properties of (Zn,Mg)TiO (ZMT) ceramics were investigated. BiVO as a sintering agent could effectively lower the firing temperature of ZMT ceramics below 930 °C. From XRD analysis, the secondary phase formation occurred when BiVO exceeding the solubility limit 2 wt% in ZMT matrix. SEM results indicated that due to the liquid phase sintering BiVO significantly improved the grain growth and densification. With an increase of BiVO, the dielectric constant (ε) monotonously increased, but the quality factor (Qf) gradually decreased, and also the temperature coefficient of resonant frequency (τ) dramatically linear degraded. Besides, the addition of CaTiO can adjust the τ value of this system to a near zero level. (ZnMg)TiO ceramic codoped with 1.5 wt% BiVO and 5 wt% CaTiO additives sintered at 930 °C exhibited the good microwave dielectric properties of ε = 23, Qf = 16177 GHz, τ ≈ 1.0 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a low-temperature co-fired ceramic (LTCC) composite based on the eutectic system BaO–ZnO–SiO2–B2O3 is fabricated. The phase formation in the LTCC composite is investigated by XRD, SEM and DSC technologies. Dielectric and thermal properties are discussed in terms of the phase composition. The results indicate that major mineral phases of the LTCC composite are barium silicate, willemite, SiO2 crystal phases and additional quartz. Due to the peculiar physical characteristics of these mineral phases, the LTCC composite can express different dielectric and thermal properties along with the evolution of the major mineral phases. [Copyright &y& Elsevier]

The influence of the TEOS (Si(OC 2 H 5) 4) addition, which decomposes into SiO 2 at high temperature, on the sintering process, morphology, and microwave dielectric properties in Y 3 Al 5 O 12 (YAG) ceramics were investigated in this work. The Y 3 Al 5 O 12 + x wt.% TEOS (0≤ x ≤ 1) ceramics were synthesized through solid-state reaction. The XRD results indicated that all YAG samples possessed a pure cubic garnet structure. The dense, pore-free crystalline microstructure of the specimen was measured by SEM. The Rietveld method was employed to refine the lattice parameters of YAG samples. Results showed that the samples' cellular parameters decreased with increasing amounts of TEOS. The addition of TEOS lowered the sintering temperature and improved the Q × f values of Y 3 Al 5 O 12 ceramics. The YAG system was added by 0.5 wt% TEOS can be exhibited excellent microwave dielectric properties with ε r =10.82, Q × f = 229,423 GHz, τ f = -29.1 ppm/°C sintering at 1670 °C for 12 h. [ABSTRACT FROM AUTHOR]

The La2O3-B2O3-ZnO (LBZ) glass was proved to be an effective sintering aid of the 0.45Ca0.6Nd0.26TiO3-0.55Li0.5Nd0.5TiO3 (CNT-LNT) ceramics. The influence of LBZ glass on the phase composition, low temperature sintering process, microstructure, activation energy, and dielectric properties of CNT-LNT ceramics was investigated in detail. The LBZ glass induced an obvious decrease of the CNT-LNT ceramics sintering temperature from 1350 to 1000 °C due to the liquid phase formation, which reduced the activation energy (Ea) of the CNT-LNT ceramics. In addition, the near zero temperature coefficient of resonant frequency (τƒ) value was obtained by adding moderate quantity of LBZ glass. CNT-LNT + 5 wt% LBZ (CNT-LNT + 5L) ceramics sintered at 1000°C/4 h displayed good microwave dielectric properties of: εr = 101.7, Q × f = 1560 GHz (f = 3.25 GHz) and τƒ = 2.3 ppm °C−1. [ABSTRACT FROM AUTHOR]

Abstract: The BaNd2Ti4O12 (BNT) solid solution containing composite additives Ba–Zn–B (BZB) were prepared as a low-temperature co-fired ceramics (LTCC). The 20wt.% addition of BZB to BNT significantly lowered the sintering temperature from 1450°C to 900°C without secondary phase formation. The sintering properties of the low-temperature sintered BNT with additives were investigated using dilatometer, scanning electron microscopy (SEM). Liquid phase was formed in the highly doped ceramics. Energy dispersive X-ray spectrometer (EDS) results further confirmed that the material was single phase which is consistent with the X-ray diffractometer (XRD) results. The specimen doped with 20wt.% BZB sintered at 900°C for 0.5h shows excellent dielectric properties: Q×f =3234GHz, ε r =63.2 and τ f =−10.9ppm/°C. [Copyright &y& Elsevier]

Abstract: Effect of ZnO ratio on the phase formation, the microstructure and microwave dielectric properties of BaO–ZnO–TiO2 ceramics with compositions varying from 1:0.5:3 to 1:0.8:3 (BaO:ZnO:TiO2) were investigated. XRD patterns show that the main crystal phase of the ceramics sintered at 1160°C to 1220°C for 2h was Ba4ZnTi11O27, accompanied by a small number of additional phases: BaZn2.03Ti3.93O10.89 and Ba2ZnTi5O13, but note that all the ceramics with different ZnO ratio sintered at 1180°C had pure Ba4ZnTi11O27 phase. SEM photographs suggest that ZnO working as sintering aids promoting the densification and grain growth, so when the proportion of ZnO was increased, the dielectric constant increased monotonically, τ f values decreased continuously and Q × f values increased first and then declined. Ceramics with composition BaO–0.6ZnO–3TiO2 sintered at 1180°C had compact and homogeneous microstructure and possessed excellent microwave dielectric properties: relative dielectric constant ɛ r =35.77, Q × f =21,288GHz and the temperature coefficient of resonant frequency τ f =1.25ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: For the purpose of sintering 0.67ZrTi2O6–0.33ZnNb2O6 ceramics in air, y(y =0.0–2.0) wt% MnCO3 was doped into it by solid-state reaction. XRD analysis suggested there were two phases: the solid solution ZrTi2O6 and the rutile TiO2. SEM analysis demonstrated MnCO3 could promote the grain growth obviously. The addition of MnCO3 had a great positive influence on the Q×f values, for example the sample with 0.7wt% MnCO3 had the highest Q × f value=44,800GHz, which was fifteen times higher than that of the undoped sample, because Mn ions worked as acceptors to receive the unwanted electrons left by the lost oxygen. The dielectric ceramics with the composition 0.67ZrTi2O6–0.33ZnNb2O6 +0.7wt% MnCO3 were sintered well at 1270°C in air and it showed good microwave dielectric properties: εr =44.4, Q × f =44,800GHz and τf =−6.8ppm/°C. Therefore, this method has the advantage over sintering ZrTi2O6–ZnNb2O6 ceramics in oxygen. [Copyright &y& Elsevier]

In this paper, ultralow dielectric constant CaMgSi 2 O 6 -KBS composites (ε r < 5) were fabricated via the solid-state route. The sintering temperature (ST) of CaMgSi 2 O 6 ceramics was successfully reduced from more than 1200 °C–850 °C with assistance of the K 2 O–B 2 O 3 –SiO 2 (KBS) glass. The impacts of KBS glass on phase compositions, microstructure, sintering activation energy and microwave dielectric properties of CaMgSi 2 O 6 ceramics were systematically discussed. The X-ray diffraction results confirmed that the (1- x)CaMgSi 2 O 6 - x KBS composites possessed CaMgSi 2 O 6 phase and SiO 2 phase. The results of Rietveld refinement showed that the weight fraction of CaMgSi 2 O 6 phase gradually decreased with increasing KBS glass and sintering temperature. The (1- x)CaMgSi 2 O 6 - x KBS (x = 0.5) composite sintered at 850 °C exhibits optimal microwave dielectric properties: ε r = 4.58, Q × f = 13989 GHz (13.95 GHz), τ f = -22.9 ppm/oC. It is a promising material for low-temperature co-fired ceramic (LTCC) applications which desire for ultralow dielectric constant materials. [ABSTRACT FROM AUTHOR]

Abstract The phase composition, microstructure, microwave dielectric properties of (Al 0.5 Nb 0.5)4+ co-substitution for Ti site in LiNb 0.6 Ti 0.5 O 3 ceramics and the low temperature sintering behaviors of Li 2 O-B 2 O 3 -SiO 2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li 1.075 Nb 0.625 Ti 0.45 O 3 solid solution was formed in all component. The increase of dielectric constant (ε r) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τ f value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb 0.6 Ti (0.5- x) (Al 0.5 Nb 0.5) x O 3 ceramics (x = 0.10) when sintered at 1100 ℃ for 2 h: ε r = 70.34, Q×f = 5144 GHz, τ f = 4.8 ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x = 0.10 were obtained with 1.0 wt% glass: ε r = 70.16, Q×f = 4153 GHz (at 4 GHz), τ f = -0.65 ppm/℃ when sintered at 925 ℃ for 2 h. [ABSTRACT FROM AUTHOR]

The influences of Li 2 O-B 2 O 3 -SiO 2 glass (LBS) on the activation energy, phase composition, the stability of the structure and microwave dielectric properties of Zn 0.15 Nb 0.3 Ti 0.55 O 2 ceramics have been systematically investigated. LBS glass acted as flux former and contributed to the reactive liquid-phase sintering mechanism, which remarkably lowed the sintering temperature from 1150 °C to 900 °C and enhanced the shrinkage and densification of ceramic at the low sintering temperatures. The ceramics with 1.5 wt% LBS glass sintered at 900 °C for 3 h show great properties: ε r = 73.59, Q × f = 8024 GHz, τ f = 270.54 ppm/°C. [ABSTRACT FROM AUTHOR]

The crystal structure of (Zn 1-x Co x ) 0.5 Ti 0.5 (Nb 1-y Ta y )O 4 microwave dielectric ceramics was determined by Rietveld refinement. The XRD results show orthorhombic structure of Zn 0.5 Ti 0.5 NbO 4 and appearance of a second phase Zn 0.17 Nb 0.33 Ti 0.5 O 2 with tetragonal structure. The relationships between the dielectric polarizability, the second phase content, bond length, bond strength, bond valence, packing fraction and microwave dielectric properties were systematically discussed. The ε r values decrease at first (x = 0, 0.1) because of the decreased polarizability and a lower relative density, while after x = 0.2, a second phase is formed, which increases the ε r to a great extent. The Q × f values drop are mainly ascribed to the decrease of packing fraction, grain size and the increase of the second phase content. With the decrease of bond valence of Ti O and oxygen octahedron distortion, the τ f values increase. Excellent microwave properties of the ceramics sintered at 1175 °C were obtained for x = 0.2 and y = 0.3: ε r = 38.02, Q × f = 23,550 GHz, τ f = 4.62 ppm/°C.Furthermore, Li 2 O B 2 O 3 SiO 2 (LBS) glass was used to lower the sintering temperature. The effects of LBS glass on the crystal structure, sintering behavior and activation energy were also discussed. These results indicate that LBS glass significantly lowers the activation energy and has no influence on the phase composition. The ceramics sintered at 900 °C for 4 h show great properties: ε r = 34.10, Q × f = 13,349 GHz, τ f = −7.12 ppm/°C, which is promising for LTCC application. [ABSTRACT FROM AUTHOR]

In the present work, the synergistic effect of Li 2 O-B 2 O 3 -SiO 2 glass (LBS) and La 2 O 3 -B 2 O 3 (LaB) addition on the wetting behavior, activation energy, phase composition, microstructure and microwave dielectric properties of the BaO-0.15ZnO-4TiO 2 ceramic (Ba-Zn-Ti) has been investigated to understand the low temperature mechanism of the sintering kinetic. The results show that co-doping with LBS and LaB decreases the activation energy and therefore accelerates the sintering process of the Ba-Zn-Ti due to the liquid phase formed at a low sintering temperature. Moreover, the co-doping of LBS and LaB restrains the appearance of BaTi(BO 3 ) 2 caused by the reaction of Ba-Zn-Ti and LBS, which has a deleterious effect on the densification and microwave dielectric properties of Ba-Zn-Ti. With LBS and LaB co-doped, the sintering temperature of Ba-Zn-Ti significantly dropped from 1150 °C to 850–900 °C and remained excellent microwave dielectric properties. [ABSTRACT FROM AUTHOR]

The sintering temperature of BaZn 2 Ti 4 O 11 ceramic (Ba-Zn-Ti) dropped from 1200 °C to 850 °C in the presence of a liquid phase containing Li 2 O and B 2 O 3 , and the ceramic remained excellent dielectric microwave properties. Experiments on the wetting behavior, activation energy, phase composition, microstructure and microwave dielectric properties of the ceramics were carried out to understand the mechanism of the sintering kinetic. The results reveal that the sintering process of the Ba-Zn-Ti significantly accelerated at a low temperature even with a higher activation energy, due to the existence of liquid phase causes decomposition of BaZn 2 Ti 4 O 11 , which provides extra energy at the early stage of sintering, called reactive liquid-phase sintering. [ABSTRACT FROM AUTHOR]

In this paper, the influences of Al substitution and BaCu(B 2 O 5 ) (BCB2) additives on the sintering temperature, microstructures, phase structures and microwave properties were investigated in detail. The results indicated that all Al added Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x Al x O 3 (CLNTA x ) samples were crystallized as orthorhombic perovskite structure in Pnma space group. A proper amount ( x ≤ 0.03) of Al substitution for Ti was beneficial to improve the quality factors mainly due to the increase of packing fraction. But the permittivity ( ε r ) and temperature coefficient of the resonant frequency ( τ f ) deteriorated because of the decrease of B-site bond valence. The perovskite structured phase and BCB2 phase were observed in Ca 0.35 Li 0.25 Nd 0.35 Ti 0.97 Al 0.03 O 3 (CLNTA3) ceramics, when a small amount of BCB2 was added ( y ≤ 5 wt%). The sintering temperature was effectively lowered under 950 °C, and τ f was modified from 74.8 ppm/°C to 41.2 ppm/°C with the assistance of BCB2 phase and liquid phase. But excessive BCB2 contents ( y > 5 wt%) resulted in the BaNd 2 Ti 5 O 14 and unknown phase, leading to inferior dielectric properties. Therefore, 5 wt% BCB2-added CLNTA3 ceramics sintered at 950 °C for 2 h exhibited excellent comprehensive microwave dielectric properties: ε r = 109.5, Q × f = 2979 GHz and τ f = 41.2 ppm/°C. [ABSTRACT FROM AUTHOR]

The influence of Li 2 O-B 2 O 3 -SiO 2 glass (LBS) on the activation energy, phase composition, reaction mechanisms, and microstructure of the BaO-0.15ZnO-4TiO 2 ceramics (Ba-Zn-Ti) were investigated to understand the mechanism of the sintering kinetic. The results reveal that the sintering process of the Ba-Zn-Ti significantly accelerated at a low temperature even with a higher activation energy, due to the reaction of Ba-Zn-Ti and LBS caused by the existence of liquid phase, which provides extra energy at the early stage of sintering, called reactive liquid-phase sintering. The sintering temperature of Ba-Zn-Ti significantly dropped from 1150 °C to 875 °C attribute to the presence of liquid phase caused by LBS, and obtained excellent dielectric microwave properties. [ABSTRACT FROM AUTHOR]

In this work, the effects of 3ZnO-2B 2 O 3 glass on sintering temperature, phase composition, microstructure and dielectric properties of Zn 1.8 SiO 3.8 ceramics were investigated. The x-ray diffraction results showed that there no reaction between the glass and the ceramic during the sintering process. A mechanism of densification and microstructure evolution of the ceramics with glass was provided based on the x-ray, density and scanning electronic microscopy results. The study on the dielectric properties showed strong dependences of glass content and sintering temperature. At last, the compact ceramic with 20 wt% glass content, exhibited a dielectric constant of 6.5 and a low loss of 0.001, after sintering at 920 °C. [ABSTRACT FROM AUTHOR]

This paper reports the investigation of the performance of Li 2 O–B 2 O 3 –SiO 2 (LBS) glass as a sintering aid to lower the sintering temperature of BaO–0.15ZnO–4TiO 2 (BZT) ceramics, as well as the detailed study on the sintering behavior, phase evolution, microstructure and microwave dielectric properties of the resulting BZT ceramics. The addition of LBS glass significantly lowers the sintering temperature of the BZT ceramics from 1150 °C to 875–925 °C. Small amount of LBS glass promotes the densification of BZT ceramic and improves the dielectric properties. However, excessive LBS addition leads to the precipitation of glass phase and growth of abnormal grain, deteriorating the dielectric properties of the BZT ceramic. The BZT ceramic with 5 wt% LBS addition sintered at 900 °C shows excellent microwave dielectric properties: ε r =27.88, Q × f =14,795 GHz. [ABSTRACT FROM AUTHOR]

Abstract: BaZn2− x Cu x Ti4O11 (x =0.00–0.14) ceramics were prepared by the conventional solid-state reaction technique and the effects of Cu2+ substitution on the crystal structure, microstructure and microwave dielectric properties of BaZn2Ti4O11 ceramics were investigated. The substitution of Cu2+ for Zn2+ in BaZn2Ti4O11 phase caused the decrease of the lattice parameters, and the adding of CuO formed the liquid-phase sintering mechanism, which effectively improved the densification process and lowered the sintering temperature. More importantly, the decrease of the lattice parameters was likely to make the bonding force and the crystal structure to become stronger, and the substitution of Cu2+ could restrain the lost of oxygen or the formation of Ti3+ ions when sintering BaZn2− x Cu x Ti4O11 ceramics at 1140–1210°C in air, thereby, both of these two reasons significantly increased the Q × f value form 10,600GHz at x =0.00–51,400GHz at x =0.02. At last, BaZn1.98Cu0.02Ti4O11 was sintered well at 1190°C for 2.5h in air and showed good microwave dielectric properties: εr =29.5, Q × f =51,400GHz and τf =−33.7ppm/°C. [Copyright &y& Elsevier]