Ultra-low Sintering Temperature Research Articles

Low permittivity MgF2-LiF ceramics with ultra-low dielectric loss for ULTCC applications

In this work, MgF2–xwt%LiF (x = 0.5, 1.0, 2.5, 4.0, 5.0) ceramics have been prepared through the standard solid-state reaction method. X-ray diffraction patterns and scanning electron micrographs revealed the successful preparation of dense MgF2–LiF composite ceramics at an exceptionally low sintering temperature range of 525–600°C. The optimal microwave dielectric properties (εr = 5.09 ± 0.03, Qf = 100,733 ± 1646 GHz, τf = −67.4 ± 3.3 ppm/°C) were achieved in MgF2–0.5 wt%LiF ceramics after sintering at 550 °C for 3 h. The present ceramics exhibited an outstanding combination of low-εr, high Qf, and an ultra-low sintering temperature, surpassing the performance of most low-temperature-fired dielectric materials. Moreover, the theoretical Qf value, extrapolated from the fitting of infrared reflectivity spectra, was calculated to be 326,583 GHz, indicating significant potential for further Qf improvement. Additionally, the chemical compatibility with Al electrodes was confirmed, suggesting promising potential for ultra-low temperature co-fired ceramic (ULTCC) applications.

Microwave dielectric properties of (Na0.5Bi0.5)MoO4–BaMoO4 composite ceramics with ultralow sintering temperature

AbstractThe rapidly ever‐growing wireless communication demands development of low loss, ultralow sintering temperature dielectric ceramics with excellent microwave properties. In this work, fabrication and properties of novel microwave dielectric composite ceramics (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 (x = 0.3–0.6), in short as ((1 − x)NBM–xBM), synthesized via solid‐state reaction method with an ultralow sintering temperature is reported. X‐ray diffraction analysis confirms the coexistence of both (Na0.5Bi0.5)MoO4 and BaMoO4 scheelite phases. Scanning electron microscopy analysis demonstrated dense microstructures of ceramics sintered at 650°C and 700°C. The dielectric properties of (1 − x)NBM–xBM (x = 0.3–0.6) ceramic are significantly tailored by incorporation of BaMoO4. With the increase in x from 0.3 to 0.6, the (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 displays noticeable change in microwave permittivity (varying from 25.4 to 16.6), quality factor values, and temperature coefficient of frequency (range tunable from +37.6 ppm/°C to −14.2 ppm/°C). The microwave dielectric ceramic, 0.5(Na0.5Bi0.5)MoO4–0.5BaMoO4, has optimum dielectric properties (, = 15 164 GHz, τf = −0.2 ppm/°C) at sintering temperature of 650°C. The dielectric resonator antenna designed using (1 − x)(Na0.5Bi0.5)MoO4–xBaMoO4 ceramics demonstrated excellent radiation performance at resonance frequency of 5.905 GHz, gain of ∼5.8 dBi and 140 MHz bandwidth, which validates its microwave applications utilization within the field of ultralow temperature cofired ceramics technology.

MgF2-based microwave dielectric ceramics with ultra-low sintering temperature and high thermal expansion coefficient

Ultralow-temperature co-fired ceramic (ULTCC) materials with low permittivity and dielectric loss are considered promising materials for 5 G communication applications. Herein, a novel multiphase xMgF2-(1x)LiF (x = 0.20, 0.35, 0.50, 0.65) microwave dielectric ceramic was prepared via a conventional solid-state method for ULTCC applications. The ceramic achieves densification at a sintering temperature of 625 °C. The xMgF2-(1-x)LiF ceramics exhibit tunable permittivity ranging from 5.21 to 7.30, Q×f from 39400 to 52800 GHz, and τf from − 61 to − 98 ppm °C−1. Analysis of the crystal structure and microstructure revealed that the volatilisation of fluoride ions in the ceramics led to an increase in defect concentration, contributing to an unfavourable decrease in dielectric loss. The 0.35MgF2-0.65LiF ceramic shows comprehensive properties with the highest Q×f value (52800 GHz) and low permittivity (6.40). Furthermore, the thermal expansion coefficient is an important performance parameter in ceramic packaging with the 0.35 MgF2-0.65 LiF ceramic exhibiting a colossal thermal expansion coefficient of 28.69 ppm °C−1, thus enabling excellent compatibility with printed circuit board (PCB) substrates. Moreover, these high thermal expansion coefficient ceramics are excellent candidates for packaging.

Hybrid low‐temperature sintering processes of electro‐ceramics

AbstractCold sintering process (CSP) developed recently has attracted much attention due to the ultralow sintering temperatures and high efficiencies with the assist of transient liquid phase (TLP). Based on CSP, we have further established a protocol for low‐temperature sintering processes by combining TLP with other sintering technologies, including hybrid sintering process with microwave and TLP (MW‐TLP), and hybrid sintering process with spark plasma sintering and TLP (SPS‐TLP). Three typical electro‐ceramics (TiO2, CaWO4, and ZnO) are selected, which are highly densified (>97%) with excellent electrical properties at reduced sintering temperatures, applied pressures or holding times, demonstrating the feasibility of MW‐TLP and SPS‐TLP in fabricating electro‐ceramics. Especially, the Q × f value of TiO2 ceramics (38,020 GHz) prepared by MW‐TLP at 1000°C is 46.2% and 23.4% higher than that of microwave and spark plasma sintered samples, respectively, and comparable to traditional thermal sintered (TTS) samples at 1300–1400°C. The dielectric properties of MW‐TLP CaWO4 ceramics sintered at 900°C for 2 h are comparable to TTS samples sintered at 1000–1300°C for 2–5 h. ZnO ceramics can be highly densified (∼98%) by SPS‐TLP with mild sintering conditions (200–300°C and 3.8–50 MPa) compared to SPS (>500°C) and CSP (>100 MPa). The frameworks of fundamental mechanisms are outlined together with the experimental data. It is expected that this work will provide promising sintering methods to fabricate electro‐ceramics and offer inspirations on sintering combinations to develop low‐temperature sintering processes with high efficiencies.

Structure, bond features, and vibrational spectra of novel K2Bi(PO4)(MoO4) microwave dielectric ceramic with ultra-low sintering temperature

This paper presents a study on the microwave dielectric properties of K2Bi(PO4)(MoO4) (KBPM) ceramics prepared through the solid-state method. XRD refinement analysis confirmed the presence of the orthorhombic crystal structure of the ceramics, belonging to space group Ibca (#73), with only the K2Bi(PO4)(MoO4) phase observed. The ceramic sintered at 625 °C exhibited the most compact structure and demonstrated excellent microwave dielectric properties: εr = 8.37, Q × f = 42,500 GHz, and τf = −78.2 ppm/°C. The measured value of εr closely matched the theoretical value, indicating a strong correlation between polarization and the εr. The Q × f value was found to be influenced by the packing fraction, while the τf value showed an inverse relationship with the Mo–O bond valence. Analysis based on the P–V-L theory revealed the interconnected nature of ionicity, lattice energy, bond energy, and the εr, Q × f, and τf of the ceramics. Raman spectroscopy provided valuable insights into the lattice vibrations of the ceramics. Additionally, the KBPM ceramics were found to possess favorable chemical compatibility with silver, suggesting their potential application as ultra-low-temperature co-fired ceramics.

Effect of Mn:Mg ratio on sintering behavior and microwave dielectric properties of (Mn, Mg)V2O6 ceramics at ultra-low sintering temperature

Effect of Mn:Mg ratio on sintering behavior and microwave dielectric properties of (Mn, Mg)V2O6 ceramics at ultra-low sintering temperature

Significant improvement on quality factor in Bi3+/Ta5+ codoped Ce2Zr3-3xBi1.5xTa1.5xMo9O36 microwave dielectric ceramics with ultra-low sintering temperatures

Molybdenum oxide-based ceramics have attracted intense interest due to ultra-low sintering temperatures. However, low quality factors (Q × f) hinder their practical applications. Although Q × f can be improved by ions doping, the sintering temperature is greatly increased. Accordingly, it is still a challenge to obtain high Q × f ceramics sintered at ultra-low temperatures (<660 °C). Herein, (Bi0.5Ta0.5)4+ ions are utilized to tackle this issue in the Ce2Zr3(MoO4)9 ceramic as a prototype. Density and scanning electron microscope (SEM) results uncover good sintering states, and X-ray diffraction (XRD) results reveal the formation of solid solutions. Interestingly, the Ce-O bonds exhibit a dominant contribution to the bond ionicity (fi), while Mo-O bonds play an important role in the lattice energy (U), the bond energy (E) and the thermal expansion coefficient (α). The remarkable increase of Q × f can be interpreted by the enhancement of the packing fraction and the mean U of Mo-O bonds. Moreover, the variations of the dielectric constant (εr) and the temperature coefficient of the resonance frequency (τf) can be explained by the variations of the intrinsic parameters. More interestingly, a negative correlation between Q × f and τf is first found. Typically, the CZ0.98B0.02 ceramic sintered at 650 °C exhibits optimum microwave dielectric properties: εr = 9.92, Q × f = 110,670 GHz, and τf = −19.20 ppm °C−1. Notably, Q × f of the Ce2Zr2.94Bi0.03Ta0.03Mo9O36 (CZ0.98B0.02) ceramic is about 6 times larger than that of the matrix while retaining a low sintering temperature of 650 °C and a low εr of 9.92, making it a promising candidate for ultra-low temperature cofired ceramics (ULTCC) applications.

Multi-material additive manufacture and microwave-assisted sintering of a metal/ceramic metamaterial antenna structure

Multi-material metal/ceramic 3D structures comprising of metallic silver and ultra-low sintering temperature silver molybdenum oxide ceramics, have been additively manufactured and hybrid densified using microwave-assisted sintering for the first time. Optimum densification conditions at 440 °C / 1 h, resulted in relative permittivity, εr = 10.99 ± 0.04, dielectric losses, tanδ = 0.005 ± 0.001 and microwave quality factor, Q × f = 2597 ± 540 GHz. Applying 2 kW microwave energy at 2.45 GHz for 60 min, was proven sufficient, to densify the metallic Ag infilling electrodes, without causing any macroscopic defects. A fully functional multi-layered antenna structure with a metamaterial artificial magnetic conductor was designed, dual-printed and densified, to showcase the potential of combining multi-material additive manufacturing with microwave-assisted sintering.

Ultra-low temperature cofired ceramics based on Li2WO4as perspective substrate materials for terahertz frequencies

With the development of low dielectric permittivity materials having an ultra-low sintering temperature, testing their dielectric properties at terahertz frequencies suitable for 6G communication systems and implementation of the fabricated materials in ultra-low temperature cofired ceramics (ULTCC) were the main goals of the research. Lithium tungstate Li₂WO₄ was synthesized by a solid-state reaction and used for the preparation of green tapes and test structures with cofired internal conductive layers, which are destined for substrates of microwave and submillimeter wave circuits. Sintering behavior, thermal effects, and mass changes of the green tapes during heating were studied using a hot-stage microscope, differential thermal analysis, and thermogravimetry. A single-phase composition was revealed for being undoped and doped with AlF₃–CaB₄O₇ ceramics. The impact of frequency, temperature, the addition of AlF₃–CaB₄O₇ and CuBi₂O₄ dopants, and sintering temperature was the subject of in-depth characterization of dielectric properties in a terahertz region. A glass-free composition, ultra-low sintering temperature of 590–630 ℃, low roughness of the green tapes, dense microstructure, compatibility with Ag conductors, low and stable dielectric permittivity of 5.0–5.8 in a broad range of 0.2–2 THz, and low dielectric loss of 0.008–0.01 at 1 THz are the main advantages of the developed ULTCC substrates.

Microwave dielectric properties of (KY)1/2MoO4 ceramics with ultra-low sintering temperature

Microwave dielectric properties of (KY)1/2MoO4 ceramics with ultra-low sintering temperature

Low-loss and ultra-low sintering temperature ceramics of AgCa1−xMgxVO4 (x = 0–0.09) for microwave applications

Low-loss and ultra-low sintering temperature ceramics of AgCa1−xMgxVO4 (x = 0–0.09) for microwave applications

Phase formation and dielectric properties of ultralow temperature sintered Li4Mo5O17 ceramics

The Li2MoO4-MoO3 ceramic system can be densely sintered at ultralow temperatures (< 500 °C). However, the phase composition of the Li2MoO4-MoO3 system at a molar ratio of 1:1 has always been controversial. In this study, the traditional solid-state method was used to synthesize Li4Mo5O17 (400 °C, 10 h) and Li2Mo2O7 (350–400 °C, 4 h). Li2Mo2O7 is an intermediate phase that can be converted to Li4Mo5O17 at higher temperatures. The Li4Mo5O17 ceramic could be sintered and densified at only 490 °C in air, exhibiting a relative density of 95.6% and excellent dielectric properties, including ε′= 12.79 and tan δ = 0.0004 at 1 GHz. Such an ultralow sintering temperature and dielectric loss indicate that the Li4Mo5O17 ceramic is a good candidate for high-frequency capacitance applications.

Low-loss microwave dielectrics of Li2(1–x)MxWO4 (M= Mg, Zn; x= 0.01–0.09) for ULTCC applications

Li2(1–x)MxWO4 (M = Mg, Zn; x = 0.01–0.09) ceramics with an ultra-low sintering temperature of 540 °C were prepared by solid-state synthesis and their structural characteristics and microwave dielectric properties were systematically investigated. By replacing Li with 0.05 mol% Mg or 0.07 mol% Zn, the sintering temperature of the Li2WO4 dielectric could be brought down from 660 to 540 °C along with the combined dielectric properties of the εr of 6.2 and 5.8, a Q × f of 76,000 and 68,000 GHz, and the τf of −94 and −86 ppm/°C, respectively. The corrected dielectric constant was found to be proportional to the ratio of αD(dielectric polarizability)/Vm(molecular volume). The results showed that the Q × f values could be dramatically improved by increasing the density, packing fraction and lattice energy. Moreover, the τf values of ceramics render a similar variation tendency by shifting linearly toward zero as the Vcation increases. The Li2(1–x)MxWO4 ceramic is a glass-free, phase pure, and energy-saving dielectric ideal for ULTCC applications.

Solid State Processing of BCZT Piezoceramics Using Ultra Low Synthesis and Sintering Temperatures.

Lead-free (Ba0.92Ca0.08) (Ti0.95 Zr0.05) O3 (BCZT) ceramics were prepared by a solid-state route (SSR) using ultra-low synthesis (700 °C/30 min and 700 °C/2 h) and sintering temperatures (from 1150 °C to 1280 °C), due to prior activation and homogenization by attrition milling of the starting high purity raw materials for 6 h before the synthesis and of the calcined powders for 3 h before the sintering. The comparison of the thermal analysis of the mixture of the starting raw materials and the same mixture after 6 h attrition milling allowed to evidence the mechanisms of activation, resulting in a significant decrease of the perovskite formation temperature (from 854 °C down to 582 °C). The secondary phases that limit the functional properties of the ceramic and their evolution with the sintering conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which allowed the design of a two-step sintering method to eliminate them. A pure tetragonal BCZT perovskite phase (P4mm, c/a = 1.004) and homogeneous ceramic microstructure was obtained for synthesis at 700 °C for 2 h and sintering with the use of a two-step sintering treatment (900 °C for 3 h and 1280 °C for 6 h). The best electromechanical properties achieved were d33 = 455 pC/N, kp = 35%, Qm = 155.

Crystal structure, Raman spectrum, bond characteristics, and terahertz time-domain spectrum of novel Na5Tm(MoO4)4 microwave dielectric ceramic with ultra-low sintering temperature and high quality factor

This study synthesized a novel Na5Tm(MoO4)4 (NTM) ceramic through the solid-state process. A single tetragonal phase of NTM ceramic was formed when sintered at 550 ℃—650 ℃. Raman spectrum studied the lattice dynamics information of NTM ceramic. The influence of multiple chemical bonds in NTM ceramic on the crystal stability and dielectric properties was revealed via the Phillips–van Vechten–Levine (P–V–L) theory. Optimal dielectric properties of εr = 7.66, Q · f = 67,499 GHz (at 10.11 GHz), and τf = − 58.85 ppm/℃ were achieved in NTM ceramic sintered at 625 ℃. According to the terahertz time-domain spectrum, the dielectric constant of NTM ceramics in the terahertz band is slightly less than that in the microwave band. Furthermore, the ceramic shows good chemical compatibility with Ag powder and is suitable for low temperature co-fired ceramic (LTCC) applications. The ultra-low sintering temperature, low dielectric constant, and low dielectric loss in the microwave and terahertz frequency bands make it an excellent dielectric material for preparing high-frequency wireless communication devices.

Preparation of an environment-friendly LTCC material by using waste soda-lime glass and natural volcanic ash

Glass/ceramic composites applied in the field of low-temperature co-fired ceramics (LTCC) were successfully prepared at 670–710 °C by using waste soda-lime glass (WG) as a binder and natural volcanic ash as a ceramic raw material. Based on the theories of suppression and supplementary network effects, alkaline-earth metal ions (R2+, R = Mg, Ca, Sr, and Ba) and B2O3 were applied to improve the dielectric properties of WG and composites, respectively. The influence of R2+ on the crystal phase evolution, microstructure, mechanical, dielectric, and thermal properties of WG-volcanic ash-based composites were systematically investigated. By doping 2.5 wt% Ba2+ to the environment-friendly LTCC composites, physical properties i.e., εr of 4.86 at 1 MHz, tan δ of 6.32 × 10−3, coefficient of thermal expansion of 8.72 × 10−6/°C, and thermal conductivity of 1.04 W/(m·K) are obtained. It is worth mentioning that the environment-friendly LTCC composite uses WG with a low glass transition temperature to reduce the sintering temperature and a tiny amount of a modifier to adjust the dielectric performance instead of synthesizing specific crystals by adding lots of chemical reagents. These, in turn, do not only have the potential to be used in the LTCC packaging technology but also have significance for sustainable development. Additionally, because of good chemical compatibility between aluminum and the composites, the environment-friendly LTCC composites with ultra-low sintering temperature have the potential ability to lower the cost of LTCC packaging materials.

Enhanced Na+-substituted Li2Mg2Mo3O12 ceramic substrate based on ultra-low temperature co-fired ceramic technology for microwave and terahertz polarization-selective functions

A novel Li2Mg2-xNa2xMo3O12 (x = 0.09) ceramic with ultra-low sintering temperature is prepared by the solid-state reaction method. This ceramic (625 °C) exhibits excellent microwave dielectric properties (εr = 7.9, Q×f = 43844 GHz, τf = −48.3 ppm/°C), terahertz transmission properties (εr1 = 7.4, tan σ1 = 0.0158, Tcoefficient = 0.598), and chemical compatibility with Ag. For the first time, two polarization selective devices are designed in the microwave and terahertz regions by using this ceramic substrate, respectively. The transmission amplitudes of the right- and left-handed circularly polarized waves of the microwave device at 9.7 GHz are 0.895 and 0.019, respectively. The transmission coefficients of the y- and x-polarized waves of the terahertz device at 0.45 THz are 0.598 and 0.075, respectively. Both functions are verified by the overall far-field radiation pattern. This work promotes the application of dielectric ceramics and ULTCC technology in the microwave and terahertz regions.

Structure-property relationships in temperature stable low firing Ag2Mo2O7-Ag0.5Bi0.5MoO4 microwave dielectric ceramics

In this work, a series of temperature stable dielectric ceramics with an ultra-low sintering temperature (480 °C) have been prepared through mixing Ag0.5Bi0.5MoO4 with Ag2Mo2O7. The XRD and SEM-EDS analysis reveal that the two phases could coexist. The microwave dielectric properties of diphase ceramics are calculated that are in a good agreement with the experimental data. Raman and infrared spectroscopic techniques are used to study the structure-property relationships from the point of the polarization mechanism. When the amount of Ag0.5Bi0.5MoO4 is 0.65, the composite ceramics sintered at 480 °C show the best temperature stability with εr = 25.7, Q × f = 16 400 GHz, tanδ = 4.31 × 10−4, and τf = 0.3 ppm/°C. In addition, the ceramics exhibit good chemical compatibility with aluminum. These results indicate that (1-x) Ag2Mo2O7-xAg0.5Bi0.5MoO4 ceramics show the excellent temperature stability among those with a sintering temperature as low as 500 °C and could be good candidates for microwave device applications.

Ultralow sintering temperature and piezoelectric properties of Bi(Zn1/2Ti1/2)O3−BiScO3−PbTiO3 for low‐temperature co‐firing applications

AbstractBi(Zn1/2Ti1/2)O3−BiScO3−PbTiO3 (BZT−BS−PT) high Curie temperature piezoelectric ceramics were synthesized by the conventional solid‐state reaction method. Systematical investigations on the sintering, piezoelectric, and dielectric properties of the piezoceramics have been conducted. It was found that the sintering temperature could be remarkably depressed by varying the compositions in BZT−BS−PT systems. For composition of 11BZT−34BS−55PT ceramic, the sintering temperature is even lowered down to 750°C without any extra additions of sintering aids. Meanwhile, the ceramic sintered at this ultralow temperature presents dense microstructure with relative density up to 97%, as well as optimal properties of piezoelectric coefficient d33 of 336 pC/N and Curie temperature of 415°C. The mechanism of low sintering temperature may be ascribed to the low melting point bismuth‐based components in BZT−BS−PT solid solutions. Furthermore, 11BZT−34BS−55PT multilayer ceramics have been co‐fired at 750°C with Ag internal electrodes. The dense structures, low cost, and optimal comprehensive properties of the co‐fired multilayers illustrate obvious advantages of the ultralow sintering temperature in LTCC devices, implying promising applications of this Bi(Zn1/2Ti1/2)O3−BiScO3−PbTiO3 high Curie temperature ternary system.

Influence of intrinsic and extrinsic factors on microwave dielectric properties of (Sr1-xMgx)V2O6 (x = 0.01–0.09) ceramics for ULTCC applications

An ultra-low sintering temperature microwave dielectric material (Sr1-xMgx)V2O6 (x = 0.01–0.09) was prepared and the effect of minutely substituting Sr with Mg on the structure, sintering temperature, densification and microstructure of the (Sr1-xMgx)V2O6 ceramic were investigated. Influence of intrinsic and extrinsic factors on the microwave dielectric properties of the ceramics were also studied. Specimens can be well-densified by sintering at 620–650 °C. XRD patterns of all specimens indicated a single α-SrV2O6 phase at all sintering temperatures. Among the compositions studied, (Sr0.93Mg0.07)V2O6 sintered at 620 °C revealed an εr ∼ 9.7, a Q × f ∼ 33,300 GHz and a τf ∼ –175 ppm/°C along with an excellent chemical compatibility with Al electrodes, which indicates the specimen might be an attractive promising candidate for ULTCC applications in particular at high frequency regions.