Search

A CaO-Al2O3-B2O3-SiO2 (CABS) glass/Al2O3 LTCC substrate material with high flexural strength for microwave application has been successfully prepared through the avenue of investigating the effects of B2O3 in CABS glass and different glass/ceramic mass ratios on sintering shrinkage behavior, phase composition, microstructure, mechanical properties, and microwave dielectric properties of CABS glass/Al2O3 composites. The results show that adding an appropriate amount of B2O3 can lower the softening temperature of CABS glass and control the interfacial reaction between CABS glass and Al2O3, which is beneficial to the densification of CABS glass/Al2O3 and improves the microwave dielectric and mechanical properties. When the content of B2O3 is 22 wt% (in the CABS glass), the CABS glass/50 wt% Al2O3 sample sintered at 875 °C for 2 h exhibits the best comprehensive properties with the dielectric constant (εr) of 6.95, dielectric loss (tanδ) of 4.56 × 10–3 (~ 10 GHz) and flexural strength of 223 MPa. [ABSTRACT FROM AUTHOR]

In this work, A-site Nd doped BaTiO3 ceramics in the form of Ba1−xNd2x/3TiO3 with a wide substitution level range of x = 0–0.2 have been prepared via solid-state reaction method. Powder X-ray diffraction results reveal that Nd is completely incorporated into the BaTiO3 lattice in all specimens. Further analyses based on Rietveld refinement suggest that tetragonal and pseudo-cubic phases coexist in Ba1−xNd2x/3TiO3 ceramics with x ≤ 0.06, and the amount of tetragonal phase is raised with the increase of x value. When x value is larger than 0.08, only pseudo-cubic is observed. The generated V Ba ″ , Nd Ba · and V O · · defects, which are identified by X-ray photoelectron spectra, make the grain size displays a tendency of decrease first mainly due to the pining effect, and then increase ascribed to the accelerate of mass diffuse. By introducing such wide range of substitution level, Ba1−xNd2x/3TiO3 ceramics with colossal dielectric constant (x = 0.08), temperature-stable dielectric properties (x = 0.15), especially relaxor behavior (x = 0.20) noticed for the first time, are, respectively, received, which is closely related to the variation of phases and defects induced by the addition of Nd. This study may provide a special idea to modify BaTiO3 to satisfy diversified applications by single element with a wide doping range, and could lay the foundation of future works focusing on the various potential applications of Ba1−xNd2x/3TiO3 ceramics. [ABSTRACT FROM AUTHOR]

Through the avenue of adjusting the thermal properties of BaO–MgO–Al2O3–SiO2 (BMAS) glass-ceramic by changing the MgO/BaO ratio, a BMAS glass-ceramic with the MgO/BaO ratio of 1:2 has been obtained, which shows satisfactory softening and crystalline behavior. Then, this BMAS glass-ceramic is used to lower the sintering temperature of Al2O3 ceramic. After systematic research on the sintering and physical properties of BMAS /Al2O3 composite with different glass-ceramic content, we find that when the content of BMAS glass-ceramic is 50%, the composite presents adorable comprehensive properties: dielectric constant of 5.40 @ ~10 GHz, dielectric loss of 1.91 × 10− 3 @ ~10 GHz and bending strength of 143 MPa, meeting the requirement of LTCC substrate material for microwave application. [ABSTRACT FROM AUTHOR]

The Ca0.245Li0.325Nd0.395Ti1−xSnxO3 (x = 0–0.12) ceramics were prepared by the traditional solid-state reaction method. The effects of Sn4+ substitution for Ti4+ on the phase composition, microstructure, and microwave dielectric properties of Ca0.245Li0.325Nd0.395Ti1−xSnxO3 (CLNTSx) were investigated in this work. The X-ray diffraction results showed that the ceramics had a single orthorhombic perovskite structure when x = 0–0.09. However, a secondary phase SnO2 was observed with x > 0.09. The SEM micrographs indicated that the proper Sn4+ substitution for Ti4+ promoted the grain growth and homogenization. The analysis results of Raman spectroscopy revealed the correlation between vibration modes and microwave dielectric properties of CLNTSx ceramics with different Sn4+ contents. The degree of cation order was related to the full width at half maximum (FWHM) of the Raman spectrum, and a lower FWHM value indicates higher cationic order and Q × f0 value. The excellent microwave dielectric properties with εr = 98, Q × f0 = 3320 GHz, and τf = 2.6 ppm/°C were obtained in the ceramics with x = 0.09 sintered at 1350 °C for 4 h. [ABSTRACT FROM AUTHOR]

BaO–Al2O3–SiO2–B2O3 (BASB) glass-ceramic designed to replace the glass additive in traditional glass + ceramic composite system as LTCC material has been investigated. The influence of additive amount of glass former B2O3, network modifier BaO and network intermediate Al2O3 on the thermodynamic properties of BASB glass-ceramics is studied. The results show that the increase of both B2O3 and BaO can lower the softening and crystallization temperatures of the glass-ceramic. At the same time, the increase of BaO content leads to the reduction in sintering shrinkage rate. The addition of Al2O3 can decrease the crystallization temperature, but the softening temperature will exhibit a complicated variation of decreasing at first and then rising. Based on the aforementioned results, an optimum BASB glass-ceramic consisting of 13 mol% B2O3, 24 mol% BaO, 12 mol% Al2O3, 50 mol% SiO2, 1 mol% ZrO2 and 1 mol% Li2O is produced, with the softening temperature of 650 °C, main crystalline phase of BaAl2Si2O8 after being sintered at 850 °C and the crystallization activation energy of 292.25 kJ/mol. The received glass-ceramic is then employed as sintering aid to fabricate low-temperature-sintered BASB glass-ceramic + Al2O3 ceramic composite. The 55 wt.% BASB + 45 wt.% Al2O3 composite sintered at 850 °C shows attractive comprehensive properties with a density of 2.79 g/cm3, dielectric constant of 5.88@10 GHz and dielectric loss of 1.54 × 10–3@10 GHz, which makes it a good candidate for microwave LTCC substrate application. [ABSTRACT FROM AUTHOR]

Low-temperature sinterable and low-loss composites consisting of La2O3–B2O3–ZnO glass-ceramics and Al2O3 filler have been investigated. The phase composition of LBZ/Al2O3 composites is closely related to the sintering temperature. When the sintering temperature was 850 °C, the main phases included LaBO3 and La(BO2)3 precipitated from LBZ glass-ceramics, ZnAl2O4 and LaAl2.03(B4O10)O0.54 phases generated by interfacial reactions, and Al2O3 filler. The high content of crystalline phases in the composites indicated the low content of residual glassy phases, which was related to the low loss of the composites at high frequencies, especially at microwave frequencies. The initial sintering temperature and the temperature corresponding to the fastest shrinkage speed of LBZ/40A and LBZ/50A composites were related to the content of LBZ glass-ceramics, and all the composites could be densified at low temperatures. Optimum properties were exhibited for the composite of LBZ glass-ceramic with 50 wt% Al2O3 sintered at 900 °C with a permittivity εr = 7.3 and a dielectric loss tan δ = 1.62 × 10−3 (at 12.1 GHz). The low εr and tanδ coupled with a low sintering temperature, suggesting that the LBZ glass-ceramic/Al2O3 composites had potential to meet the requirements of LTCC substrate materials for high frequencies. [ABSTRACT FROM AUTHOR]

The sintering behavior and dielectric properties of La2O3–B2O3–CaO–P2O5 (LBCP) glass and La2O3–B2O3–CaO–P2O5 glass/Al2O3 (LBCP/A) composites have been investigated. The results show that the major crystalline phase of LBCP glass–ceramics sintered at 625 °C is low-temperature LaBO3 phase, and it transits to high-temperature LaBO3 phase with the sintering temperature up to 850 °C. With the increase of La/B ratio in LBCP glass, the crystallization tendency of LaBO3 phase increases. LBCP/A composites could be well sintered at 850 °C for 2 h. The bulk density of LBCP/A composites increases with the glass content rising and then decreases owing to foaming. The main crystalline phases of LBCP/A composites are LaBO3, CaAl2B2O7, and Al2O3. Dielectric properties are related to the glass composition and content, which determines the density of the composites. The optimized dielectric properties of LBCP/A composites are dielectric constant of 7.108 and dielectric loss of 1.024 × 10–3 in 50LBCP3/50A, which nicely meet the requirements of LTCC substrate materials. [ABSTRACT FROM AUTHOR]

The microstructure and dielectric properties of LaMnO3 (LM) doped BaTiO3 (BT) ceramics have been investigated. By adding LM, (1–x)BT-xLM (x = 0–0.5) ceramics keep in a single-phase solid-solution state, but gradually transform from tetragonal structure to pseudocubic one, and much denser microstructure is obtained. As for dielectric properties, when x ≤ 0.1, the Curie temperature of BT-LM shifts to a lower temperature and the permittivity maximum is lowered with the increase of LM content, which are attributed to the introduction of La2O3 and the degradation of tetragonality, respectively. When x > 0.1, BT–LM presents a typical relaxation behavior. Colossal permittivity appears as x reaches 0.4, which is related to large number of giant electron-pinned defect-dipoles ( Mn 4 + · 2 e - V O · · ) and existence of grain-boundary segregation. Detailed analyses show that 0.5BT–0.5LM possesses the highest permittivity maximum (41,683) and widest temperature range (– 42 to 300 °C) with permittivity larger than pure BT at 100 kHz. Therefore, 0.5BT–0.5LM can be a very promising candidate as colossal permittivity material. [ABSTRACT FROM AUTHOR]

To have a better understanding on the characteristics of La2O3–B2O3–CaO (LBC) glass–ceramics designed for low temperature co-fired ceramic applications, LBC glass–ceramics with La/B ratio changing from 1:6.0 to 1:3.0 were prepared, and the network structure, sinterability, crystalline phase composition and crystallization kinetics of synthesized LBC glass–ceramics were investigated. The increase of La/B ratio would reduce the content of [BO4] units in the network structure, and decrease the glass transition temperature as well as the softening temperature of LBC glass–ceramics. But low La/B ratio of glass could cause serious foaming during sintering process. The change of La/B ratio would influence the position as well as intensity of crystalline peaks on DSC curves, and the composition and microstructure of crystalline phases were also affected. The crystallization activation energies of LBC glass–ceramics were 157.9–498.7 kJ/mol, which raised up with the increase of La/B ratio. [ABSTRACT FROM AUTHOR]

The sintering densification behaviors and crystallization characteristics of CBS glass have been investigated systematically, and a new CBS glass composite system containing two types of CBS glass is reported. The results demonstrated that the sintering densification characteristic of single CBS glass and CBS composite could be divided into two stages: the fast and slow densification stage. The temperature range of the fast densification stage of single CBS glass is quite narrow (680–710 °C), while CBS composite gets a wider one (680–730 °C). In result, more moderate sintering densification process, which benefits the co-firing compatibility with electrode materials, is obtained in CBS composite. The major crystalline phases of the CBS glass and CBS composite were CaSiO3 and CaB2O4. CBS glass sintered at 910 °C for 10 min exhibited excellent microwave dielectric properties of dielectric constant value of 6.4 and quality factor value of 11,110 GHz, while CBS composite showed dielectric properties of dielectric constant value of 6.1 and quality factor value of 10,640 GHz, which meets the requirements for LTCC applications. [ABSTRACT FROM AUTHOR]

New glass-ceramic/ceramic composites based on lead-free low-softening La2O3-B2O3-Al2O3 (LBA) glass-ceramics and Al2O3 fillers were prepared. The phase compositions, microstructure, and dielectric properties of the composites were investigated. LaBO3, La(BO2)3 and LaAl2.03(B4O10)O0.54 including Al2O3 fillers were developed in the LBA glass-ceramics/alumina composites sintered at 875 °C, but the relative amounts of the phases varied greatly with different glass-ceramic compositions and were considered to be determined by the ratio of La2O3 to B2O3. The onset sintering temperatures of green composites were ~ 670 °C and the sintering shrinkage of the samples was mainly determined by the low-softening glass-ceramics. Optimum properties were exhibited for the composite of 25 La2O3-65 B2O3-10 Al2O3 glass-ceramic with 40 wt% Al2O3 sintered at 900 °C with a permittivity εr = 7.91, a dielectric loss tan δ = 2.12 × 10−3 (at 8.1 GHz). The low εr and tan δ coupled with a low sintering temperature, suggested that the LBA glass-ceramic/Al2O3 composites were potential candidates for LTCC applications. [ABSTRACT FROM AUTHOR]

Glass + ceramic composites based on low-softening-point borosilicate (BS) glass, β-spodumene and Al2O3 were produced in this work. The influence of ceramic filler composition on the microstructure, sintering quality, mechanical properties, thermal properties and dielectric properties of composites were studied. XRD and DSC indicated that both kinds of ceramic filler as well as the BS glass maintained their characteristics after sintering. The addition of β-spodumene would decrease the coefficient of thermal expansion (CTE) value of composites to match with silicon well. The better wetting behavior between β-spodumene and BS glass would lead to better sintering quality, microstructure and dielectric properties for composites containing more β-spodumene. With appropriate Al2O3 content, the flexural strength of composites could be enhanced. Composite with 45 wt% BS glass, 30 wt% β-spodumene and 25 wt% Al2O3 sintered at 875 °C showed good properties which meet the requirements of low temperature co-fired ceramic applications: dense microstructure with high relative density of 96.27%, proper CTE value of 3.57 ppm/°C, high flexural strength of 156 MPa, low dielectric constant of 6.20 and low dielectric loss of 1.9 × 10−3. [ABSTRACT FROM AUTHOR]

The effects of BiBO addition on the sintering temperature, phase transition and microwave dielectric properties of BaO-NdO-4TiO (BNT) ceramics have been investigated. With 10 wt% BiBO addition, the sintering temperature of the BNT ceramics can be lowered down to about 1,150 °C. The secondary phase was observed at the level of 15 wt% BiBO addition. The BiBO addition can significantly affects the microwave dielectric properties. The Q × f value is a function of the sintering temperature and the BiBO content. For the samples sintered at 1,150 °C, Q × f value varies from 6,300 to 3,300 GHz as the BiBO addition increases from 5 to 20 wt%. The addition of BiBO does not induce much degradation in ε but modified the τ value to near zero. Typically, When 10 wt% BiBO is added, the τ of the ceramics could be tuned to a near-zero value (~1.2 ppm/°C), a substantial ε (~86) and Q × f (~4,670 GHz) could also be achieved simultaneously. The BiBO is an efficient sintering additive to decrease the sintering temperature and tune the τ value of the microwave dielectric materials for the practical microwave applications. [ABSTRACT FROM AUTHOR]