A Novel Glass‐Ceramic with Ultra‐Low Sintering Temperature for LTCC Application

In this paper, the phase compositions and the dielectric properties of 3ZnO–2B₂O₃ glass‐ceramic prepared by solid‐state method were investigated. The X‐ray diffraction patterns show that all sintered samples consist of Zn₃B₂O₆ and α‐Zn(BO₂)₂. The dielectric properties changed significantly with the sintering temperature. After sintering at 650°C for 30 min, the glass‐ceramic exhibits optimum dielectric properties: a dielectric constant of 7.5 and a dielectric loss of 0.6 × 10^?3 at 10 MHz. The chemical compatibility with Ag electrode under the co‐fired process illustrates a potential application in low temperature co‐fired ceramic field for the glass‐ceramic.     

Carbon nanotube/graphene oxide‐added CaO‐B2O3‐SiO2 glass/Al2O3 composite as substrate for chip‐type supercapacitor

A CaO‐B₂O₃‐SiO₂ (CBS) glass/40 wt% Al₂O₃ composite sintered at 900°C exhibited a dense microstructure with a low porosity of 0.21%. This composite contained Al₂O₃ and anorthite phases, but pure glass sintered at 900°C has small quantities of wollastonite and diopside phases. This composite was measured to have a high bending strength of 323 MPa and thermal conductivity of 3.75 W/(mK). The thermal conductivity increased when the composite was annealed at 850°C after sintering at 900°C, because of the increase in the amount of the anorthite phase. 0.25 wt% graphene oxide and 0.75 wt% multi‐wall carbon nanotubes were added to the CBS/40 wt% Al₂O₃ composite to further enhance the thermal conductivity and bending strength. The specimen sintered at 900°C and subsequently annealed at 850°C exhibited a large bending strength of 420 MPa and thermal conductivity of 5.51 W/(mK), indicating that it would be a highly effective substrate for a chip‐type supercapacitor.     

New Sintered Li2O–Al2O3–SiO2 Ultra‐Low Expansion Glass‐Ceramic

We developed a new Li₂O–Al₂O₃–SiO₂ (LAS) ultra‐low expansion glass‐ceramic by nonisothermal sintering with concurrent crystallization. The optimum sintering conditions were 30°C/min with a maximum temperature of 1000°C. The best sintered material reached 98% of the theoretical density of the parent glass and has an extremely low linear thermal expansion coefficient (0.02 × 10^?6/°C) in the temperature range of 40°C–500°C, which is even lower than that of the commercial glass‐ceramic Ceran^® that is produced by the traditional ceramization method. The sintered glass‐ceramic presents a four‐point bending strength of 92 ± 15 MPa, which is similar to that of Ceran^® (98 ± 6 MPa), in spite of the 2% porosity. It is white opaque and does not have significant infrared transmission. The maximum use temperature is 600°C. It could thus be used on modern inductively heated cooktops.     

Sintering and Dielectric Properties of Li2O–B2O3–Al2O3–SiO2 Glass‐Added (Ca0.7Sr0.3O)1.03(Ti0.1Zr0.9)O2 for Copper Electrode

When 1.5 wt% of Li₂O–B₂O₃–SiO₂ and 1.5 wt% of Li₂O–B₂O₃–Al₂O₃ glass‐added (Ca_0.7Sr_0.3O)_1.03(Ti_0.1Zr_0.9)O₂ batch was ball milled for 10~30 h followed by sintering at 950°C in flowing N₂‐10%H₂ atmosphere, an apparent density of approximately 4.5 g/cm³, a dielectric constant of approximately 26, and a quality factor of roughly about 3300 GHz were demonstrated. A prolonged ball mill time thereafter significantly decreased both of the dielectric properties because of the enhanced reduction of the specimens during sintering. The apparent evidence of a material reaction between the dielectric material and the copper electrode was not observed.     

Effects of ZnO and B2O3 on the Microstructure and Microwave Dielectric Properties of 5Li2O‐1Nb2O5‐5TiO2 Ceramics

The effects of ZnO and B₂O₃ addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li₂O‐1Nb₂O₅‐5TiO₂ (LNT) ceramics have been investigated. With addition of low‐level doping of ZnO and B₂O₃, the sintering temperature of the LNT ceramics can be lowered down to near 920°C due to the liquid phase effect. The Li₂TiO₃ss and the “M‐phase” are the two main phases, whereas other phase could be observed when co‐doping with ZnO and B₂O₃ in the ceramics. And the amount of the other phase increases with the ZnO content increasing. The addition of ZnO does not induce much degradation in the microwave dielectric properties but lowers the τ_f value to near zero. Typically, the good microwave dielectric properties of ε_r = 36.4, Q × f = 8835 GHz, τ_f = 4.4 ppm/°C could be obtained for the 1 wt% B₂O₃ and 4 wt% ZnO co‐doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as internal electrode.     

Dielectric Properties of Ultra‐Low Sintering Temperature Al2O3–BBSZ Glass Composite

Ceramic composites of B₂O₃–Bi₂O₃–SiO₂–ZnO (BBSZ) glass mixed with Al₂O₃ (10–50 vol%) were sintered at 450°C, and their microstructural and dielectric properties investigated. Dense structures were obtained when the Al₂O₃ content was lower than 30 vol%. Raman, XRD, and FESEM showed the existence of a secondary phase, Bi₂₄Si₂O₄₀, in all samples. The dielectric properties of the composite with 30 vol% addition of Al₂O₃ showed good dielectric properties with ε_r of 14.8 and 20.8 and 32.5 at 100 kHz and 100 MHz and 1 GHz, respectively. The tanδ values at the same frequencies were 0.004 and 0.006 and 0.016. The results show that BBSZ glass with different amounts of Al₂O₃ exhibit widely applicable relative permittivity values and affordable loss and are thus promising candidates for ultra‐low sintering temperature applications.     

Glass Additive Influence on the Sintering Behaviors,Magnetic and Electric Properties of Bi–Zn Co‐Doped Co2Y Ferrites

The Bi₂O₃–B₂O₃–ZnO–SiO₂ (BB35SZ) glass effects on the sintering behavior and magnetic properties of Bi–Zn co‐doped Co₂Y ferrites were investigated in developing low‐temperature‐fired ferrites. The results indicate that BB35SZ glass can be used as a sintering aid to reduce the densification temperature of Co₂Y ferrites from 1300°C to 900°C. The 2(Ba_0.9Bi_0.1O)·2(Zn_0.4Co_0.4Cu_0.2O)·6(Fe_1.97Zn_0.03O₃) ferrite with 4 wt% BB35SZ glass can be densified below 900°C, exhibiting an initial permeability of 3.4 and quality factor of 55. This process provides a promising candidate for multilayer chip magnetic devices for microwave applications.     

Low‐Temperature Sintering Microwave Characteristics of B2O3‐doped CaLa4Ti4O15 Dielectric Ceramics

Preparation and microwave dielectric properties of B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics have been investigated. X‐ray diffraction data show that CaLa₄Ti₄O₁₅ ceramic has a trigonal structure coupled with a second phase of CaLa₄Ti₅O₁₇. The CaLa₄Ti₄O₁₅ ceramic with addition of 0.5 wt% B₂O₃, sintered at 1220°C for 4 h, exhibits microwave dielectric properties with a dielectric constant of 45.8, Q × f value of 24,000 GHz, and temperature coefficient of resonant frequency (τ_f) of ?19 ppm/^°C. B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics, which have better sintering behavior (decrease in sintering temperature ~ 330°C) and dielectric properties than pure CaLa₄Ti₄O₁₅ ceramics, are candidates for applications in microwave devices.     

Effect of Sintering Additives on Relative Density and Li‐ion Conductivity of Nb‐Doped Li7La3ZrO12 Solid Electrolyte

Lithium ion conductors with garnet‐type structure are promising candidates for applications in all solid‐state lithium ion batteries, because these materials present a high chemical stability against Li metal and a rather high Li⁺ conductivity (10^?3–10^?4 S/cm). Producing densified Li‐ion conductors by lowering sintering temperature is an important issue, which can achieve high Li conductivity in garnet oxide by preventing the evaporation of lithium and a good Li‐ion conduction in grain boundary between garnet oxides. In this study, we concentrate on the use of sintering additives to enhance densification and microstructure of Li₇La₃ZrNbO₁₂ at sintering temperature of 900°C. Glasses in the LiO₂‐B₂O₃‐SiO₂‐CaO‐Al₂O₃ (LBSCA) and BaO‐B₂O₃‐SiO₂‐CaO‐Al₂O₃ (BBSCA) system with low softening temperature (<700°C) were used to modify the grain‐boundary resistance during sintering process. Lithium compounds with low melting point (<850°C) such as LiF, Li₂CO₃, and LiOH were also studied to improve the rearrangement of grains during the initial and middle stages of sintering. Among these sintering additives, LBSCA and BBSCA were proved to be better sintering additives at reducing the porosity of the pellets and improving connectivity between the grains. Glass additives produced relative densities of 85–92%, whereas those of lithium compounds were 62–77%. Li₇La₃ZrNbO₁₂ sintered with 4 wt% of LBSCA at 900°C for 10 h achieved a rather high relative density of 85% and total Li‐ion conductivity of 0.8 × 10^?4 S/cm at room temperature (30°C).     

Influence of Li2O–B2O3–SiO2 glass on the sintering behavior and microwave dielectric properties of BaO–0.15ZnO–4TiO2 ceramics

This paper reports the investigation of the performance of Li₂O–B₂O₃–SiO₂ (LBS) glass as a sintering aid to lower the sintering temperature of BaO–0.15ZnO–4TiO₂ (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.     

Low‐temperature sintering and thermal stability of Li2GeO3‐based microwave dielectric ceramics with low permittivity

A low‐permittivity dielectric ceramic Li₂GeO₃ was prepared by the solid‐state reaction route. Single‐phase Li₂GeO₃ crystallized in an orthorhombic structure. Dense ceramics with high relative density and homogeneous microstructure were obtained as sintered at 1000‐1100°C. The optimum microwave dielectric properties were achieved in the sample sintered at 1080°C with a high relative density ~ 96%, a relative permittivity ε_r ~ 6.36, a quality factor Q × f ~ 29 000 GHz (at 14.5 GHz), and a temperature coefficient of resonance frequency τ_f ~ ?72 ppm/^°C. The sintering temperature of Li₂GeO₃ was successfully lowered via the appropriate addition of B₂O₃. Only 2 wt.% B₂O₃ addition contributed to a 21.2% decrease in sintering temperature to 850°C without deteriorating the dielectric properties. The temperature dependence of the resonance frequency was successfully suppressed by the addition of TiO₂ to form Li₂TiO₃ with a positive τ_f value. These results demonstrate potential applications of Li₂GeO₃ in low‐temperature cofiring ceramics technology.     

Ba5Li2W3O15: A New Li‐Containing Perovskite‐Type Microwave Ceramic with High Q and Low τf

A new Li‐containing microwave ceramic Ba₅Li₂W₃O₁₅ with hexagonal perovskite structure was prepared through a solid‐state ceramic route. Small amount of scheelite BaWO₄ appeared as a second phase during sintering. The Ba₅Li₂W₃O₁₅ could be well densified at 1120°C and exhibits good microwave dielectric properties with permittivity (ε_r) of 25.4, high Q × f value about 39 000 GHz, and low temperature coefficient of resonate frequency (τ_f) of 10 ppm/°C. The addition of BaCu(B₂O₅) can effectively lower the sintering temperature from 1120°C to 900°C and does not induce degradation of the microwave dielectric properties. These results indicate that the Ba₅Li₂W₃O₁₅ ceramic might be a promising candidate in microwave dielectric resonators.     

Microwave Dielectric Properties of Novel Glass‐Free Low‐Firing Li2CeO3 Ceramics

Novel glass–free low temperature firing microwave dielectric ceramics Li₂CeO₃ with high Q prepared through a conventional solid‐state reaction method had been investigated. All the specimens in this paper have sintering temperature lower than 750°C. XRD studies revealed single cubic phase. The microwave dielectric properties were correlated with the sintering conditions. At 720°C/4 h, Li₂CeO₃ ceramics possessed the excellent microwave dielectric properties of ε_r = 15.8, Q × f = 143 700 (GHz), and τ_f  = ?123 ppm/°C. Li₂CeO₃ ceramics could be excellent candidates for glass‐free low‐temperature co‐fired ceramics substrates.     

Low‐Fire Processing of Microwave BNBT‐Based High‐k Dielectric with Li2O–ZnO–B2O3 Glass

The effects of Li₂O–ZnO–B₂O₃ (LZB) glass addition on densification and dielectric properties of Ba₄(Nd_0.85Bi_0.15)_9.33Ti₁₈O₅₄ (BNBT) have been investigated. At a given ratio of ZnO/B₂O₃, the glass softening point decreases, but the thermal expansion coefficient and dielectric constant increase with increasing Li₂O content in the LZB glass. With 10 vol% LZB glass, the densification temperature reduces greatly from 1300°C for pure BNBT to 875°C–900°C for BNBT + LZB dielectric, and the densification enhancement becomes more significant with increasing Li₂O content in the LZB glass. The above result is attributed to a chemical reaction taking place at the interface of LZB/BNBT during firing, which becomes less extensive with increasing Li₂O content in the LZB glass. Therefore, more residual LZB glass, which acts as a densification promoter to BNBT, is left with increasing Li₂O content. For the LZB glass with a Li₂O content in the range 10–30 mol%, the resulting 90 vol% BNBT + 10 vol% LZB microwave dielectric has a dielectric constant of 55–70, product (Q × f_r) of quality factor (Q) and resonant frequency (f_r) of 1000–3000 GHz at 5–5.79 GHz, and a temperature coefficient of resonant frequency (τ_f) of 10–60 ppm/°C in the temperature range between 25°C and 80°C.     

Ultra‐Low Fire Glass‐Free Li3FeMo3O12 Microwave Dielectric Ceramics

A new ultra‐low fire glass‐free microwave dielectric material Li₃FeMo₃O₁₂ was investigated for the first time. Single phase ceramics were obtained by the conventional solid‐state route after sintering at 540°C–600°C. The atomic packing fraction, FWHM of the A_g oxygen‐octahedron stretching Raman mode and Qf values of samples sintered at different temperatures correlated well with each other. The sample with a Lower Raman shift showed a higher dielectric constant. Interestingly, the system also showed a distinct adjustable temperature coefficient of resonant frequency (from ?84× 10^?6/°C to 25 × 10^?6/°C).     

Sealing Glass‐Ceramics with Near‐Linear Thermal Strain,Part II: Sequence of Crystallization and Phase Stability

The sequence of crystallization in a recrystallizable lithium silicate sealing glass‐ceramic Li₂O–SiO₂–Al₂O₃–K₂O–B₂O₃–P₂O₅–ZnO was analyzed by in situ high‐temperature X‐ray diffraction (HTXRD). Glass‐ceramic specimens have been subjected to a two‐stage heat‐treatment schedule, including rapid cooling from sealing temperature to a first hold temperature 650°C, followed by heating to a second hold temperature of 810°C. Notable growth and saturation of Quartz was observed at 650°C (first hold). Cristobalite crystallized at the second hold temperature of 810°C, growing from the residual glass rather than converting from the Quartz. The coexistence of quartz and cristobalite resulted in a glass‐ceramic having a near‐linear thermal strain, as opposed to the highly nonlinear glass‐ceramic where the cristobalite is the dominant silica crystalline phase. HTXRD was also performed to analyze the inversion and phase stability of the two types of fully crystallized glass‐ceramics. While the inversion in cristobalite resembles the character of a first‐order displacive phase transformation, i.e., step changes in lattice parameters and thermal hysteresis in the transition temperature, the inversion in quartz appears more diffuse and occurs over a much broader temperature range. Localized tensile stresses on quartz and possible solid‐solution effects have been attributed to the transition behavior of quartz crystals embedded in the glass‐ceramics.     

Dielectric Properties and Low‐Temperature Sintering of the Ba0.6Sr0.4TiO3 Ceramics with B2O3/CuO Additions

The sintering behaviors and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated as a function of B₂O₃ and CuO content. The addition of both B₂O₃ and CuO reduced the sintering temperature of Ba_0.6Sr_0.4TiO₃ about 500°C. It was suggested that a liquid phase BaCu(B₂O₅) was formed and assisted the densification of Ba_0.6Sr_0.4TiO₃ ceramics. Ba_0.6Sr_0.4TiO₃ ceramics co‐doped with 3.0 mol% B₂O₃, and 2.0 mol% CuO, sintered at 950°C for 5 h, had a dense microstructure and showed good microwave dielectric properties of a moderate dielectric constant (ε = 1048), low dielectric loss (0.0090) and high tunability (42.2%) at dc electric field of 30 kV/cm.     

The structures and dielectric properties of Ba0.80Sr0.20TiO3/Pb0.82La0.18TiO3 composite thick films with addition of PbO–B2O3 glass

Sol–gel derived Ba_0.80Sr_0.20TiO₃ (BST) and Pb_0.82La_0.18TiO₃ (PLT) powders and a low-melting PbO–B₂O₃ glass powder were mixed to prepare paste. The composite thick films (∼40 μm) were fabricated by screen-printing the paste onto the Al₂O₃ substrates with screen-printed silver bottom electrode and then sintered at the low temperature 650–800 °C, respectively. X-ray diffraction (XRD), transmission microscope (TEM), scanning electron microscope (SEM) and an impedance analyzer were used to analyze the structures, microstructures and dielectric properties of the powders and the composite thick films. The results show that the composite thick films containing sol–gel derived Ba_0.80Sr_0.20TiO₃ and Pb_0.82La_0.18TiO₃ perovskite phases have been fabricated by using the PbO–B₂O₃ glass as a sintering aid. Compared to conventional sintering at ≥1200 °C, high densification of the composite thick films is achieved at temperature as low as 800 °C by the “wetting” and “infiltration” of the liquid phase on the particles. The homogenization of the BST and PLT perovskite phase in the composite thick films is evitable by controlling the sintering temperature and time. The formation of the small amount of pyrochlore phase in composite thick films sintered at 800 °C is resulted from both the volatilization of PbO and the interaction between the PLT and PbO–B₂O₃ glass. The relative dielectric properties of the composite thick films exhibit good temperature-stable behavior, and the variation of the relative dielectric constant is less than 10% in the temperature range 0–300 °C.     

Development of a lead‐free copper co‐fired BNT‐based piezoceramic sintered at low temperature

Compatibility of Bi‐based piezoelectric ceramic and copper electrodes is demonstrated by co‐firing 0.88Bi_1/2Na_1/2TiO₃–0.08Bi_1/2K_1/2TiO₃–0.04BaTiO₃ (BNKBT88) with copper. A combination of Bi₂O₃, CuO, ZnO, Li₂CO₃, and B₂O₃ are used as additives to reduce firing temperature to 900°C with minimal effect on the electromechanical properties compared to sintering at 1150°C without additives. Co‐firing with copper electrodes requires controlled oxygen sintering at low temperature. The atmosphere is controlled using carbon dioxide and hydrogen gas to maintain an oxygen partial pressure of 6.1 × 10^?8 atm, which is necessary for the coexistence of Cu metal and Bi₂O₃. The thermodynamic activity of bismuth oxide in BNKBT88 is calculated to be 0.38. BNKBT88 ceramics were successfully co‐fired with internal as well as surface Cu metal electrodes. The copper co‐fired ceramics were successfully polarized and the dielectric and piezoelectric properties are evaluated.     

Ba0.7Sr0.3TiO3–glass–silver percolative composite

Ba_0.7Sr_0.3TiO₃–glass–silver (BST–glass–Ag) composites were prepared by the solid state ceramic route. Their percolation behavior and dielectric properties were examined. The pure BST had a percolation limit of 24 vol% of silver whereas an addition of 8 wt% of 50PbO–30B₂O₃–20SiO₂ (PBS) glass lowered the percolation limit to 14 vol% of Ag. Glass addition lowered the sintering temperature of BST from 1300 to 975 °C and addition of Ag further lowered the sintering temperature to 925 °C, minimizing the Ag loss during sintering. The relative permittivity increased from 2700 for pure BST to about five orders of magnitude in the BST–glass–Ag composites near the percolation threshold.