A novel low-firing microwave dielectric ceramic Li2ZnGe3O8 with cubic spinel structure

A Li₂ZnGe₃O₈ ceramic was investigated as a promising microwave dielectric material for low-temperature co-fired ceramics applications. Li₂ZnGe₃O₈ ceramic was prepared via the conventional solid-state method. X-ray diffraction data shows that Li₂ZnGe₃O₈ ceramic crystallized into a cubic spinel structure with a space group of P4₁32. Dense ceramic with a relative densities of 96.3% were obtained when sintered at 945 °C for 4 h and exhibited the optimum microwave properties with a relative permittivity (ε_r) of 10.3, a quality factor (Q × f) of 47,400 GHz (at 13.3 GHz), and a temperature coefficient of resonance frequency (τ_f) of −63.9 ppm/°C. The large negative τ_f of Li₂ZnGe₃O₈ ceramic could be compensated by rutile TiO₂, and 0.9Li₂ZnGe₃O₈–0.1TiO₂0·1TiO₂ ceramic sintered at 950 °C for 4 h exhibited improved microwave dielectric properties with a near-zero τ_f of −1.6 ppm/°C along with ε_r of 11.3 and a Q × f of 35,800 GHz (11.6 GHz). Moreover, Li₂ZnGe₃O₈ was found to be chemically compatible with silver electrode when sintered at 945 °C.     

A novel high-Q oxyfluoride Li4Mg2NbO6F microwave dielectric ceramic with low sintering temperature

Novel low-fired Li₄Mg₂NbO₆F ceramics were synthesised using a conventional solid-state reaction method. X-ray diffraction and Rietveld refinement confirmed that the Li₄Mg₂NbO₆F compound had a face-centred-cubic rock salt structure [Fm-3 m(225)] above 625 °C. Li₄Mg₂NbO₆F ceramics sintered between 875 °C and 950 °C displayed the optimised density (> 97.5 %). The theoretical ε_theo was calculated based on the refined crystal parameters, closing to the measured ε_r. The ceramic sintered at 900 °C exhibited excellent microwave dielectric properties with ε_r of 15.53 ± 0.03, Q × f value of 93,300 ± 1100 GHz (at 7.7 GHz) and τ_f value of ?39.8 ± 0.8 ppm/°C. The compatibility with Ag powders makes the oxyfluoride a potential candidate for LTCC applications.     

A low-sintering temperature microwave dielectric ceramic for 5G LTCC applications with ultralow loss

In next-generation mobile and wireless communication systems, low sintering temperature and excellent dielectric properties are synergistic objectives in the application of dielectric resonators/filters. In this work, Li₂Ti_0·98Mg_0·02O_2·96F_0.04–1 wt% Nb₂O₅ (LTMN) ceramics were fabricated, and their sintering temperature was successfully lowered from 1120 °C to 750 °C by adjusting the mass ratio of B₂O₃–CuO (BC) additive. The optimum dielectric properties (ԑ_r ~ 24.44, Q × f ~ 60,574 GHz and τ_f ~ 22.8 ppm/°C) were obtained in BC-modified LTMN ceramics sintered at 790 °C. Even if their sintering temperature was lowered to 750 °C, the lowest temperature among the Li₂TiO₃-based dielectric ceramics currently used for LTCC technology, excellent dielectric properties (ԑ_r ~ 23.77, Q × f ~ 51,636 GHz) were still maintained. Additionally, no extra impurity phase was detected in BC-modified LTMN ceramics co-fired with Ag at 790 °C, indicating that BC-modified LTMN ceramics have a bright prospect in high-performance LTCC devices for 5G applications.     

A new BaB2O4 microwave dielectric ceramic for LTCC application

To satisfy the requirements of miniaturization and integration of microwave devices, microwave dielectric ceramics with low sintering temperatures and good microwave dielectric properties are particularly important for LTCC materials. In this study, low-cost BaB₂O₄ ceramics were prepared with different Ba/B ratios using a solid-phase method. Combined with the Raman spectra, the effects of the Raman shift and FWHM of the vibration peaks on the microwave dielectric properties were determined. As a novel microwave dielectric ceramic, BaB₂O₄ consists of a highly dense structure with optimal microwave dielectric properties (ε_r = 4.06, Q×f = 23845 GHz, and τ_f = −7.2 ppm/℃) at a low sintering temperature (840 ℃). In addition, BaB₂O₄ ceramic is chemically compatible with Ag, making it a promising candidate substrate for microwave communications.     

A low-εr and high-Q microwave dielectric ceramic Li2SrSiO4 with abnormally low sintering temperature

A novel low-temperature co-fired ceramic Li₂SrSiO₄ with low-ε_r and high-Q was synthesized through solid-state reaction. XRD results showed that the Li₂SrSiO₄ ceramic formed a single hexagonal structure with a space group of P3₁21. The microwave dielectric properties of Li₂SrSiO₄ ceramic sintered at 880 °C were ε_r = 7.4 ± 0.1, Q × f = 100,700 ± 2000 GHz, and τ_f = −85.4 ± 2.4 ppm/℃. The PVL chemical bond theory indicated that the low sintering temperature of Li₂SrSiO₄ ceramic might be ascribed to the weak covalency (18 %) of SiO bond. A near-zero τ_f (‒1.9 ± 1.8 ppm/℃) combined with ε_r = 8.2 ± 0.1, and Q × f = 63,200 ± 1900 GHz was obtained by adding SrTiO₃ to form 0.94Li₂SrSiO₄ - 0.06SrTiO₃ composite ceramic. Given their chemical compatibility with Ag powders, the Li₂SrSiO₄ ceramics can be a candidate dielectric material for LTCC applications.     

Enhancement of structural and microwave properties of Zn2+ ion-substituted Li2MgSiO4 ceramics for LTCC applications

In this study, Zn²⁺-substituted Li₂MgSiO₄ ceramics (Li₂(Mg_1-xZn_x)SiO₄, x = 0.00, 0.05, 0.10, 0.15, and 0.20) were synthesized using a traditional solid-state method. A fixed amount of LiF sintering aid (1.5 wt%) was added to the ceramics for decreasing the sintering temperature and adjusting their microwave dielectric properties. X-ray diffraction (XRD) results revealed no secondary phases, and scanning electron microscopy (SEM) data suggest that the Zn²⁺ ion substitution increased the size and uniformity of the grains, thereby affecting the densification of the prepared ceramics. The maximum bulk density (2.94 g/cm³) was found in a Zn²⁺ ion-substituted ceramic with x = 0.10 at a relative density of 94.2% (compared with the XRD theoretical density). Excellent microwave dielectric properties (ε_r = 6.28, Q × f = 50400 GHz, and τ_f = ?145 ppm/°C) can also be obtained at this zirconium content. We believe that the developed ceramics are promising for use as antenna substrates or transmit/receive modules in low-temperature co-firing ceramic applications.     

A novel low-loss Ba12InNb9O36 microwave dielectric ceramic with 18-layer hexagonal perovskite structure

A novel Ba₁₂InNb₉O₃₆ microwave dielectric ceramic is prepared by a solid-state reaction method. Rietveld refinement and transmission electron microscopy confirm that Ba₁₂InNb₉O₃₆ crystallizes as an 18-layer hexagonal perovskite structure with a stacking sequence (cccchh)₃ for the BaO₃ layers. A dense and compact microstructure is observed for the Ba₁₂InNb₉O₃₆ ceramic, when sintered at 1470 °C, with an optimal relative density of 96.84 %. The intrinsic dielectric constant and dielectric loss are investigated based on the infrared reflectivity spectrum. The microwave dielectric properties of ε_r = 36.12, Q × f = 57,250 GHz (at f = 6.24 GHz), and τ_f = 17.58 ppm/°C are obtained, rendering Ba₁₂InNb₉O₃₆ ceramic a promising candidate material for microwave electronic devices.     

Synthesis and microwave dielectric properties of Bi2Ge3O9 ceramics for application as advanced ceramic substrate

During the synthesis of Bi₂Ge₃O₉ ceramics using Bi₂O₃ + 3GeO₂ powders, the Bi₄Ge₃O₁₂ phase was formed at low temperature (≤800 °C). Bi₄Ge₃O₁₂ preferentially adopted GeO₂-excess phase, and this phase was consistently present in the sintered Bi₂Ge₃O₉ ceramic as a secondary phase. Therefore, Bi₄Ge₃O₁₂ powder was first calcined and subsequently reacted with GeO₂ powder to obtain the pure Bi₂Ge₃O₉ ceramic through the following reaction: 1/2Bi₄Ge₃O₁₂ + 3/2GeO₂ → Bi₂Ge₃O₉. Formation of the Bi₂Ge₃O₉ phase was initiated at temperature of 850 °C. The pure Bi₂Ge₃O₉ ceramic sintered at 875 °C for 8 h had a dense microstructure with an average grain size of 2.7 μm. Furthermore, the pure Bi₂Ge₃O₉ ceramic exhibited promising microwave dielectric properties for the advanced ceramic substrate: ε_r = 9.7, Q × f = 48,573 GHz and τ_f = −29.5 ppm/°C.     

Improved microstructure and high quality factor of Li2Ti0.9(Zn1/3Ta2/3)0.1O3 microwave ceramics with LiF additive for LTCC applications

In this study, LiF was utilized to decrease sintering temperature, improve microstructure, enhance Q×f, and regulate τ_f of Li₂Ti_0.9(Zn_1/3Ta_2/3)_0.1O₃ (abbreviated as LTZT) ceramics. A complete solid solution together with a phase transition from monoclinic to cubic rock salt structure occurred. The cell volume of LTZT ceramics decreased as the LiF content increased. Relatively dense and uniform microstructures were observed for the ceramics as the LiF content was not less than 2 wt%. The dielectric constant of LTZT ceramics initially increased and then decreased with the increasing LiF content. The FWHM of the Raman band at about 808 cm^?1 was closely related to the Q×f value. Notably, the samples with 3 wt% LiF exhibited the highest relative density of 97.4 % and satisfactory microwave dielectric properties of ε_r = 23.14 ± 0.16, Q×f = 110,090 ± 1100 GHz, and τ_f = +3.25 ± 1.45 ppm/°C when sintered at 950 °C. Good chemical compatibility with silver indicated the ceramic is a promising candidate in LTCC applications.     

A novel low-loss microwave dielectric ceramic Ba16ZrNb12O48

A novel Ba₁₆ZrNb₁₂O₄₈ ceramic is synthesized by a solid-state sintering method. The phase composition, microstructure, infrared reflectivity spectrum and microwave dielectric properties of Ba₁₆ZrNb₁₂O₄₈ ceramic sintered at 1400−1500℃ are investigated. The differential scanning calorimetry and X-ray diffraction analysis indicate that Ba₁₆ZrNb₁₂O₄₈ crystallizes in the hexagonal perovskite structure with space group R-3 m at 1250℃. As the temperature increases, the permittivity and Q × f value exhibit a strong relevance to the relative density. The satisfactory microwave dielectric properties of ε_r = 36.85, Q × f = 57,000 GHz (at f = 6.50 GHz), and τ_f = 48 ppm/℃ are obtained when the specimen is sintered at 1450℃, which renders Ba₁₆ZrNb₁₂O₄₈ a potential candidate for microwave electronic devices.     

Chemical bond characteristics and infrared reflectivity spectrum of a novel microwave dielectric ceramic CaIn2O4 with near-zero τf

Orthorhombic-structured CaIn₂O₄ ceramics with a space group Pca2₁ were synthesized via a solid-state reaction method. A high relative density (95.6 %) and excellent microwave dielectric properties (ε_r ～11.28, Qf = 74,200 GHz, τ_f ～ ?4.6 ppm/°C) were obtained when the ceramics were sintered at 1375 °C for 6 h. The dielectric properties were investigated on the basis of the Phillips–Van Vechten–Levine chemical bond theory. Results indicated that the dielectric properties were mainly determined by the InO bonds in the CaIn₂O₄ ceramics. These bonds contributed more (74.65 %) to the dielectric constant than the CaO bonds (25.35 %). Furthermore, the intrinsic dielectric properties of the CaIn₂O₄ ceramics were investigated via infrared reflectivity spectroscopy. The extrapolated microwave dielectric properties were ε_r ～10.12 and Qf = 112,200 GHz. Results indicated that ion polarization is the main contributor to the dielectric constant in microwave frequency ranges.     

A new Li-based ceramic of Li4MgSn2O7: Synthesis,phase evolution and microwave dielectric properties

A pure-phase Li₄MgSn₂O₇ (L₄MS) was successfully synthesized through optimizing the calcination condition. Microwave dielectric properties of the L₄MS ceramic with the phase evolution were investigated together with its low-temperature sintering. The sample maintains a single L₄MS phase as sintered below 1200?°C, such that τ_f remains a constant value of ～12.4?ppm/°C. Accompanied by the appearance of impurity phases (Li₂SnO₃)_ss and especially (MgO)_ss at higher sintering temperatures, excellent microwave dielectric properties of ε_r?=?13.1–13.5, Q?×?f?=?106,800–126,810?GHz and τ_f ?=?0–?4.2?ppm/°C are obtained in samples sintered at 1215–1260?°C for 4?h. Reduction of sintering temperature using LiF sintering aid also helps achieve pure-phase dense L₄MS ceramic. The L₄MS?+?x wt.% LiF ceramic exhibits ε_r～13.7, Qxf～97,000?GHz (x?≤?3) and τ_f ～8–13?ppm/°C sintered at 850?°C for potential LTCC applications, and ε_r ～13.9, Qxf～146,000?GHz and τ_f ～1.5–6?ppm/°C (x?≥?4) as sintered 1000?°C, exhibiting large potentials for microwave dielectric candidates.     

Design and fabrication of a C-band patch antenna using novel low permittivity SrGa2Si2O8 microwave dielectric ceramic

A novel microwave dielectric ceramic of SrGa₂Si₂O₈ was synthesized using the traditional solid-state method. Its phase composition, microstructure, and microwave dielectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and network analyzer. XRD results indicated that the space group of the ceramic transformed from I₂/c to P₂₁/a at 700 °C. A combination of good microwave dielectric properties was obtained at 1260 °C with ε_r = 6.3, Q×f= 96,600 GHz and τ_f = −45.2 ppm/°C at 16.5 GHz. The negative τ_f can be tuned to near zero by adding 15 mol% CaTiO₃. The densification temperature can be reduced to 940 °C by adding 4 wt% LiF. Moreover, the SrGa₂Si₂O₈ ceramic had good chemical compatibility with the Ag electrode. A patch antenna was designed using the 0.85SrGa₂Si₂O₈ + 0.15CaTiO₃ + 4 wt% LiF ceramic. The antenna had a high radiation efficiency of 99.2 % and a gain of 2.988 dBi at the center frequency of 4.261 GHz. All results indicated that the SrGa₂Si₂O₈ ceramic has promising potential for applications in 5 G wireless communication technology.     

Significantly enhanced sinterability and temperature stability of Li3Mg4NbO8-based microwave dielectric ceramics with LiF and Ba3(VO4)2 addition

Li₃Mg₄NbO₈-basic composite ceramics were elaborated via the solid-state reaction process, in which LiF and Ba₃(VO₄)₂ were utilized as a sintering aid and reinforcement phase, respectively. The sinterability, phase assemblage, microstructures, and microwave dielectric performances of Li₃Mg₄NbO₈–LiF–Ba₃(VO₄)₂ composite ceramics were thoroughly researched. The co-addition of LiF–Ba₃(VO₄)₂ can simultaneously lower the sintering temperature and improve the thermal stability of Li₃Mg₄NbO₈-basic ceramics. Solid state activated sintering is responsible for the low-temperature densification of the present ceramics. The coexistence of rock-salt structural Li₃Mg₄NbO₈/Li₄Mg₄NbO₈F and hexagonal structural Ba₃(VO₄)₂ phases was demonstrated by the combinational XRD and SEM-EDS analysis results. The 0.65(Li₃Mg₄NbO₈–LiF)-0.35Ba₃(VO₄)₂ ceramics fired at 825 °C/5 h exhibited promising microwave dielectric performances: τ_f = 0.5 ppm/°C along with ε_r = 13.8 and Qxf = 68500 GHz. The good compatibility of the developed ceramics with Ag demonstrates it potential for use in LTCC technology.     

Intrinsic dielectric behavior of Mg2TiO4 spinel ceramic

In the work, we focused on the intrinsic dielectric behavior of Mg₂TiO₄ spinel ceramic by P–V–L theory and infrared spectra analysis. Ti–O bonds have larger bond ionicity values, thus playing an important role in dielectric polarization. The theoretical dielectric constant was predicted by calculating the bond susceptibility of each chemical bond. Furthermore, Ti(1)–O bonds are responsible for the structural stability of Mg₂TiO₄ ceramic. Based on classical dispersion theory, permittivity and loss corresponding to each infrared active mode were quantified, and then the crucial contribution of low-frequency modes to intrinsic dielectric properties were determined.     

A novel low-loss Ba12SbNb9O36 microwave dielectric ceramic with 18-layer hexagonal perovskite structure

A novel low-loss Ba₁₂SbNb₉O₃₆ microwave dielectric ceramic is synthesized via the solid-state reaction method. TG-DSC thermal analysis is employed to study the phase formation process of the samples. The XRD and TEM analyses reveal that the ceramic samples all confirmed a hexagonal perovskite structure with the R-3 m space group. The refinement result shows that the ceramic is a shifted hexagonal perovskite with an 18-layer structure. Porosity has an important impact on permittivity and dielectric loss in this ceramic. Raman spectroscopy revealed that the quality factor shows a close connection with the FWHM of the A_1g mode at 777 cm^?1. XPS analysis shows that the oxidation of Sb ions deteriorates the τ_f value of the ceramic. The optimum microwave dielectric properties (ε_r = 35.59, Q × f = 58,297 GHz and τ_f = +34.14 ppm/°C) are obtained by sintering at 1250 °C, making the Ba₁₂SbNb₉O₃₆ ceramic a promising candidate for high-performance microwave applications.