Microwave dielectric properties of silico-carnotite Ca3M2Si3O12 (M= Yb,Y) ceramics synthesized via high energy ball milling

The Ca₃M₂Si₃O₁₂ (M = Yb, Y) ceramics with orthorhombic silico-carnotite structure were fabricated via high-energy ball milling and solid-state reaction route. Dense Ca₃Yb₂Si₃O₁₂ and Ca₃Y₂Si₃O₁₂ ceramics sintered at 1260 °C and 1240 °C revealed promising microwave dielectric properties with ε_r = 9.2 and 8.7, Q×f = 56,400 GHz and 29,094 GHz, τ_f = −77.5 ppm/°C and −76.8 ppm/°C, respectively. The connection between crystal structure and Q×f values of Ca₃M₂Si₃O₁₂ (M = Yb, Y) ceramics was discussed with respect to the packing fraction, and their intrinsic microwave dielectric properties were examined using the infrared reflectivity spectra analysis. The thermal stability of Ca₃Yb₂Si₃O₁₂ was improved successfully by forming 0.91Ca₃Yb₂Si₃O₁₂‐0.09CaTiO₃ composite ceramics with τ_f = +2.9 ppm/°C, ε_r = 12.93 and Q×f = 26,729 GHz.     

Microwave dielectric properties of Ca1.15RE0.85Al0.85Ti0.15O4 (RE=Nd,La, Y) ceramics prepared by the reaction sintering method

Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics were prepared by a reaction sintering method. The sintering behavior, phase composition, microstructure and microwave dielectric performances of ceramics were investigated. X-ray diffraction patterns illustrated that both the Ca_1.15Nd_0.85Al_0.85Ti_0.15O₄(CNAT) and Ca_1.15Y_0.85Al_0.85Ti_0.15O₄(CYAT) ceramics are single-phase structures, and the Ca_1.15La_0.85Al_0.85Ti_0.15O₄(CLAT) ceramic contain LaAlO₃ and CaO phases. The apparent morphology and elemental distribution of the ceramic samples were analyzed by using scanning electron microscope and energy dispersive spectrometer. When the sintering temperature is 1500 °C, the CNAT and CYAT ceramics have the best microwave dielectric properties with ε_r = 19.2, Q × f = 74924 GHz, τ_f = ?1.21 ppm/°C and ε_r = 17.5, Q × f = 27440 GHz, τ_f = ?5.79 ppm/°C, respectively. And the best microwave dielectric properties of ε_r = 17.5, Q × f = 22568 GHz, τ_f = ?14.69 ppm/°C were obtained for the CLAT ceramic sintered at 1525 °C. The reaction sintering method provides a low-cost, economical and straightforward method for the preparation of the Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics, which has promising potential for application.     

Structure and dielectric properties of novel low temperature co-fired Bi2O3-RE2O3-MoO3 (RE=Pr,Nd, Sm,and Yb) based microwave ceramics

Novel monoclinic Bi₂O₃-xRE₂O₃-yMoO₃ (RE=Pr, Nd, Sm, and Yb) based low temperature co-fired ceramics (LTCC) systems with high sintering density and low microwave dielectric loss are synthesized by conventional solid state reaction technique. The structure and dielectric properties of Bi₂O₃-xRE₂O₃-yMoO₃ ceramics are investigated. Dense BiNdMoO₆ ceramics sintered at 900 °C for 8 h in air have a low dielectric constant ε_r=~7.5, a high quality factor Q×f=~ 24, 800 GHz at 7.0 GHz, and τ_f=~−16 ppm/̊C. Especially, good chemical compatibility of BiNdMoO₆ with Ag electrodes is represented as well. In contrast, BiSmMoO₆ ceramics sintered at 1000 °C for 8 h show enhanced Q×f=~43, 700 GHz at 7.8 GHz with ε_r=~8.5 and τ_f=~−27 ppm/°C. Bi₂O₃-xRE₂O₃-yMoO₃ (RE=Pr, Nd, Sm, and Yb) based ceramics could be considered as promising microwave ceramics for LTCC applications.     

Crystal structure and microwave dielectric properties of garnet-type Ca2YZr2-xTixAl3O12 ceramics for dual-band bandpass filters

Microwave dielectric ceramics with a high-quality factor are vital materials for substrates, dielectric resonators, and filters in millimeter-wave communication systems. Here, a novel microwave dielectric ceramic based on a garnet-type Ca₂YZr₂Al₃O₁₂ compound for bandpass filter was prepared using the solid-state reaction method. Sintering the Ca₂YZr₂Al₃O₁₂ ceramics at 1600 ℃ for 5 h resulted in excellent microwave dielectric properties of ε_r = 10.81 ± 0.16, Qf = 87,628 ± 4000 GHz and τ_f = ?34.3 ± 0.5 ppm/℃. Increasing the Ti⁴⁺ content of the Ca₂YZr_2-xTi_xAl₃O₁₂ ceramics significantly improved the sintering process. Superior microwave dielectric properties (ε_r = 11.93 ± 0.15, Qf = 121,930 ± 2600 GHz and τ_f = ?30.8 ± 0.4 ppm/℃) were obtained for Ca₂YZr_2-xTi_xAl₃O₁₂ (x = 0.3) because of its dense microstructure, large grain size and high lattice energy. The Ca₂YZr_2-xTi_xAl₃O₁₂ (x = 0.3) ceramics were used to fabricate a dual-band bandpass filter with a hairpin structure that exhibited a large return loss (|S₁₁| > 12 dB) and a small insertion loss (|S₂₁| < 0.73 dB). The high performance of the Ca₂YZr_2-xTi_xAl₃O₁₂ ceramics and the corresponding bandpass filter makes this material a potential candidate for millimeter-wave devices.     

Structure and microwave dielectric properties of novel walstromite-type MCa2Si3O9 (M = Ba,Sr) ceramics

Novel walstromite-type MCa₂Si₃O₉ (M = Ba, Sr) ceramics, with triclinic space group P-1, were prepared through a solid-state reaction method. The P–V-L theory proves that the lattice energy and bond energy of the Si–O bond play a leading role in the quality factor and the dielectric constant is mainly determined by the ionic polarization. Excellent microwave dielectric properties of BaCa₂Si₃O₉ and SrCa₂Si₃O₉ ceramics could be obtained: ε_r = 8.99 ± 0.23, Q × f = 44,542 ± 500 GHz, and τ_f = −25.9 ± 3.0 ppm/°C and ε_r = 7.39 ± 0.23, Q × f = 48,772 ± 500 GHz, and τ_f = −27.5 ± 3.0 ppm/°C, when sintered at 1240/1280 °C for 4 h. Then SrCa₂Si₃O₉ ceramic is applied to a new microstrip bandpass filter, because of its high microwave dielectric properties and low thermal expansion coefficient. With reduced dimension, the filtering performance of the circuit is also highly improved, including reduced capacitor parasitic effect and the optimized stopband insertion loss. Accordingly, the SrCa₂Si₃O₉ ceramic is a promising candidate for sub-6 GHz a filter of microstrip bandpass applications.     

Modulation of microwave dielectric properties in melilite-structured SrREGa3O7 (RE = La,Pr) ceramics

Gallium-based SrREGa₃O₇ (RE = La, Pr) melilite ceramics were prepared and selected to modify their microwave dielectric properties. Sintered at 1425 °C for 6 h, SrLaGa₃O₇ (SLGO) and SrPrGa₃O₇ (SPGO) ceramics exhibited high relative densities of 98.33 and 95.23%, low ε_r values of 11.8 and 10.9, Q×f values of 32,500 GHz (at 12.1 GHz) and 26,400 GHz (at 12.7 GHz), negative τ_f values of ?32 and ?54 ppm/°C. As a compensator, CaTiO₃ can tune the τ_f values of SLGO and SPGO to near zero (+2 and ?4 ppm/°C). In SrREGa₃O₇ melilite ceramics, the ε_r and τ_f values are mainly dependent on ionic polarizability, crystal structure and the “rattling” effect. The micromorphology, XPS, Raman spectrum and A-site bond valence (V_RE) of SrREGa₃O₇ (RE = La, Pr) microwave dielectric ceramics have also been comprehensively reported.     

Principal element design of garnets to access structure stability and excellent microwave dielectric properties

Guided by the tolerance factor and average electronegativity difference, two stable garnets with compositions Ca₃BTiGe₃O₁₂ (B = Mg, Zn) were designed, synthesized followed by structural, and dielectric characterization. The phase purity and structural characteristics were analyzed using X-ray, Rietveld refinement, and microstructural analysis through scanning electron microscopy. A cubic structure with an Ia-3d space group was confirmed for synthesized compositions. A combination of microwave dielectric properties for both garnets suggested that Ca₃MgTiGe₃O₁₂ ceramic possessed a much higher quality factor (Q × f) ∼ 84 000 ± 3000 GHz coupled by a higher dielectric constant (ε_r) ∼ 12.97 ± 0.03, and a smaller temperature coefficient of resonance frequency (τ_f) ∼ −29.4 ± 1.5 ppm/°C compared to its Zn counterpart (Q × f ∼ 45 000 ± 2000 GHz, ε_r ∼ 12.84 ± 0.03, and τ_f ∼ −33.19 ± 1.6 ppm/°C). Such differences in dielectric performances were further explored utilizing packing fraction, ion polarizability, bond valence, Raman, and infrared spectrum to understand structure–property relationship.     

Correlation between crystal structure and microwave dielectric properties of two garnet-type ceramics in rare-earth-free gallates

Two garnet-type rare-earth-free ceramics, Ca₃M₂SiGa₂O₁₂ (M = Sn and Zr), were prepared through a solid-state reaction method. The relationship between crystal structure and microwave dielectric properties was investigated. The larger deviation of ε_r from ε_theo in Ca₃Zr₂SiGa₂O₁₂ could be ascribed to the rattling Zr⁴⁺. The increase in packing fraction and the decrease in FWHM enhance the Q × f value by substituting Zr⁴⁺ with Sn⁴⁺. The smaller oxygen bond valence in Ca₃Zr₂SiGa₂O₁₂ indicates a smaller τ_f value. Good microwave dielectric properties are obtained with ε_r = 9.14 ± 0.02, Q × f = 106,800 ± 1700 GHz and τ_f = -45.8 ± 1.8 ppm/°C for Ca₃Sn₂SiGa₂O₁₂ and ε_r = 11.98 ± 0.03, Q × f = 84,200 ± 1500 GHz, and τ_f = -32.8 ± 1.4 ppm/°C for Ca₃Zr₂SiGa₂O₁₂. Furthermore, near-zero τ_f values of +5.7 ± 1.9 ppm/°C and +4.5 ± 1.6 ppm/°C appear in 0.95Ca₃Sn₂SiGa₂O₁₂-0.05CaTiO₃ and 0.96Ca₃Zr₂SiGa₂O₁₂-0.04CaTiO₃, respectively.     

Li4Mg3Ti2O9: A novel low-loss microwave dielectric ceramic for LTCC applications

Low-loss novel Li₄Mg₃Ti₂O₉ dielectric ceramics with rock-salt structure were prepared by a conventional solid-state route. The crystalline structure, chemical bond properties, infrared spectroscopy and microwave dielectric properties of the abovementioned system were initially investigated. It could be concluded from this work that the extrinsic factors such as sintering temperatures and grain sizes significantly affected the dielectric properties of Li₄Mg₃Ti₂O₉ at lower sintering temperatures, while the intrinsic factors like bond ionicity and lattice energy played a dominant role when the ceramics were densified at 1450 °C. In order to explore the origin of intrinsic characteristics, complex dielectric constants (ε^’ and ε^’’) were calculated by the infrared spectra, which indicated that the absorptions of phonon oscillation predominantly effected the polarization of the ceramics. The Li₄Mg₃Ti₂O₉ ceramics sintered at 1450 °C exhibited excellent properties of ε_r=15.97, Q·f=135,800 GHz and τ_f=−7.06 ppm/°C. In addition, certain amounts of lithium fluoride (LiF) were added to lower the sintering temperatures of matrix. The Li₄Mg₃Ti₂O₉−3 wt% LiF ceramics sintered at 900 °C possessed suitable dielectric properties of ε_r=15.17, Q·f =42,800 GHz and τ_f=−11.30 ppm/°C, which made such materials promising for low temperature co-fired ceramic applications (LTCC).     

Crystal structures,bond characteristics,and dielectric properties of novel middle-εr Ln3NbO7 (Ln = Nd,Sm) microwave dielectric ceramics with opposite temperature coefficients

This study synthesized two novel middle-ε_r Ln₃NbO₇ (Ln = Nd, Sm; named NNO and SNO) microwave dielectric ceramics through the classic solid-state process. The results of XRD and Rietveld refinement show that NNO and SNO ceramics formed pure phases with the space group Cmcm (63) and C222₁ (20), respectively. The properties of Ln-O and Nb–O bonds of NNO and SNO ceramics were calculated based on the P–V–L theory. The Nb–O bonds positively affect the crystal structure stability of the two ceramics. The optimum microwave dielectric properties were obtained (NNO: ε_r = 31.61, Q·f = 6,615 GHz (at 6.10 GHz), and τ_f = ?455.70 ppm/°C; SNO: ε_r = 34.55, Q·f = 11,625 GHz (at 5.77 GHz) and τ_f = 72.59 ppm/°C) when the samples sintered at 1550 °C. Notably, SNO ceramic shows a low dielectric loss and medium dielectric constant, and the opposite τ_f of NNO and SNO ceramics provide the possibility to fabricate microwave dielectric devices with good temperature stability.     

Effects of ionic polarizability and crystal structure on microwave dielectric properties of RE2O3 (RE = La,Eu) ceramics with opposite τf and high Q

Hexagonal La₂O₃ and monoclinic Eu₂O₃ ceramics were prepared, and their microwave dielectric properties were investigated. La₂O₃ sintered at 1400 °C exhibited promising microwave dielectric properties of ε_r = 18.6, Q×f = 71,400 GHz, and a negative τ_f of − 35.1 ppm/°C, while Eu₂O₃ sintered at 1500 °C possessed relative lower ε_r and Q×f values of 17.9 and 35,000 GHz, respectively, with an abnormally positive τ_f of + 19.6 ppm/°C. The difference in their microwave dielectric properties is mainly due to lattice-induced strain, which can be characterized by bond valence. To investigate the degradation of RE₂O₃ (RE = La, Eu) ceramics in air, a series of La_2−xEu_xO₃ (x = 0.5, 1, and 1.5) ceramics were prepared. The results of the present study suggest that the introduction of Eu³⁺ effectively prevents the decomposition of La₂O₃.     

Microwave dielectric properties of Re3Ga5O12 (Re: Nd,Sm, Eu,Dy and Yb) ceramics and effect of TiO2 on the microwave dielectric properties of Sm3Ga5O12 ceramics

Re₃Ga₅O₁₂ (Re: Nd, Sm, Eu, Dy and Yb) garnet ceramics sintered at 1350–1500 °C had a high quality factor (Q × f) ranging from 40,000 to 192,173 GHz and a low dielectric constant (ɛ_r) of between 11.5 and 12.5. They also exhibited a relatively stable temperature coefficient of resonant frequency (τ_f) in the range of −33.7 to −12.4 ppm/°C. In order to tailor the τ_f value, TiO₂ was added to the Sm₃Ga₅O₁₂ ceramics, which exhibited good microwave dielectric properties. The relative density and grain size increased with addition of TiO₂, resulting in the enhancement of Q × f value. The τ_f increased with the addition of TiO₂. Excellent microwave dielectric properties of ɛ_r = 12.4, Q × f = 240,000 GHz and τ_f = −16.1 ppm/°C were obtained from the Sm₃Ga₅O₁₂ ceramics sintered at 1450 °C for 6 h with 1.0 mol% TiO₂. Therefore, Re₃Ga₅O₁₂ ceramics, especially TiO₂-added Sm₃Ga₅O₁₂ ceramics are good candidates for advanced substrate materials in microwave integrated circuits (MICs) applications.     

Raman spectra,bond characteristics,and microwave dielectric properties of Gd2Mo3O12 ceramics

Gd₂Mo₃O₁₂ ceramics were prepared using the traditional solid-phase reaction method. All samples were found to possess an orthorhombic crystal structure with a space group of Pba2, as revealed by refined XRD results. The ceramic sintered at 1000 °C exhibited a high relative density of 96.95 % and superior microwave dielectric properties, including ε_r of 9.42 ± 0.05,  × f of 49258 ± 1200 GHz, and τ_f of −71.8 ± 0.7 ppm/°C. The results suggest a correlation between an increase in ε_r and higher relative density, and a more compact and uniform microstructure can lead to higher  × f value. Chemical bonding theories and Raman spectroscopy analysis reveal that Mo-O bonds, rather than Gd-O bonds, dominate the microwave dielectric properties. Furthermore, the ε_r of Gd₂Mo₃O₁₂ ceramic was closely related to bond ionicity, while  × f and τ_f were mainly determined by lattice energy and bond energy, respectively.     

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.     

Structure,microwave dielectric properties,and infrared reflectivity spectrum of olivine type Ca2GeO4 ceramic

Ca₂GeO₄ dielectric ceramic was prepared using the conventional solid-state reaction method. Sintering behavior, crystal structure, microstructure, and microwave dielectric properties were analyzed by XRD, SEM, Raman, and Infrared reflectivity spectrum. Ca₂GeO₄ was found to crystallize in the olivine structure with a space group of Pnma. A dense and high-performance microwave dielectric property with permittivity ? 6.76 ± 0.02, Q×f value ? 82,400 ± 1800 GHz, and temperature coefficient ? -67 ± 3.4 ppm/°C were obtained in the sample sintered at 1420 °C. Infrared spectral analysis supported that the dielectric contribution for Ca₂GeO₄ at microwave region is dominated by absorption of phonons and there is no contribution from dipolar or other polarization mechanisms. The large negative τ_f values could be compensated by forming composite ceramics with CaTiO₃. A low-ε_r of 9.02 ± 0.03, a high Q×f of 49,880 ± 1400 GHz, and a near-zero τ_f value of +4 ± 0.6 ppm/°C were obtained for 0.92Ca₂GeO₄-0.08CaTiO₃ ceramic at 1420 °C for 4 h. This ceramic could be a good candidate for microwave substrate materials.     

High-performance 0.9Al2O3-0.1TiO2 microwave dielectric ceramics prepared by digital light processing

In this work, the 0.9Al₂O₃-0.1TiO₂ ceramic sample with good microwave dielectric properties and complex structures can be well fabricated by digital light processing (DLP). A relationship between dispersant content and rheological behavior of 0.9Al₂O₃-0.1TiO₂ slurry was explored. When dispersant content was 3.0 wt%, 0.9Al₂O₃-0.1TiO₂ slurry with high solid loading (50 vol%) and low viscosity (2.9 Pa s) could be obtained. 0.9Al₂O₃-0.1TiO₂ ceramic parts with high accuracy were fabricated successfully by adding 3.0 wt% photoinitiator under 600 mJ/cm² exposure energy. With the increase of sintering temperature from 1400 °C to 1600 °C, relative density, dielectric constant (ε_r), and quality factor (Q × f) of 0.9Al₂O₃-0.1TiO₂ ceramic sample increased first and then decreased, and all reached the maximum value at 1550 °C due to the uniformity and densification of microstructures. The temperature coefficient of resonant frequency (τ_f) value showed an almost monotonous increase, changing from negative to positive, and near-zero τ_f value at 1550 °C. In addition, 0.9Al₂O₃-0.1TiO₂ ceramic samples sintered at 1550 °C fabricated by DLP method presented much better microwave dielectric properties: ε_r = 11.30 ± 0.02, Q × f = 35,345 ± 143 GHz (@～12 GHz), τ_f = 2.16 ± 0.21 ppm/°C than that of by dry pressing method: ε_r = 11.16 ± 0.11, Q × f = 30,195 ± 257 GHz (@～12 GHz), τ_f = 4.45 ± 0.13 ppm/°C, especially the Q × f value achieved a 17% increase. Accordingly, DLP technique, which has advantages of producing relatively high properties and complex geometry of microwave dielectric ceramics as well as without extra high-cost mold, greatly satisfies application requirements.     

Effects of sintering parameters and Nd doping on the microwave dielectric properties of Y2O3 ceramics

Y₂O₃ ceramics with good dielectric properties were prepared via co-precipitation reaction and subsequent sintering in a muffle furnace. The effects of Nd doping and sintering temperature on microwave dielectric properties were studied. With the increase in sintering temperature, the density, quality factor (Q×f), and dielectric constant (ε_r) values of pure Y₂O₃ ceramics increased to the maximum and then gradually decreased. The Y₂O₃ ceramics sintered at 1500 °C for 4 h showed optimal dielectric properties: ε_r=10.76, Q×f=82, 188 GHz, and τ_f=−54.4 ppm/°C. With the addition of Nd dopant, the Q×f values, ε_r, and τ_f of the Nd: Y₂O₃ ceramics apparently increased, but excessive amount degraded the quality factor. The Y₂O₃ ceramics with 2 at% Nd₂O₃ sintered at 1460 °C displayed good microwave dielectric properties: ε_r=10.4, Q×f=94, 149 GHz and τ_f=−46.2 ppm/°C.     

Microwave dielectric properties of Li3A3Te2O12 (A = Y,Yb) garnets for low temperature cofired ceramic technologies

Te⁶⁺-containing microwave dielectric ceramics Li₃A₃Te₂O₁₂ (A = Y, Yb) with low firing temperatures were prepared using the solid-state reaction method. Li₃Y₃Te₂O₁₂ and Li₃Yb₃Te₂O₁₂ can be obtained as garnet single-phase ceramics with low sintering temperatures of 940 ℃ and 950 ℃, respectively. The cations, such as Li⁺, Te⁶⁺, and Y³⁺/Yb³⁺, fully occupied the tetrahedral, octahedral, and dodecahedral sites of garnet structure, respectively. Li₃A₃Te₂O₁₂ (A = Y, Yb) ceramics exhibit ε_r ～ 7.83 ± 0.2 and 5.94 ± 0.2, Q × f ～ 47,800 ± 500 GHz and 41,800 ± 500 GHz, and τ_f ～ –47 ± 3.0 ppm/°C and –76 ± 3.0 ppm/°C, respectively. The full width at half-maximum (FWHM) values of the A_1g Raman mode correlate negatively with the Q × f values. Moreover, Li₃A₃Te₂O₁₂(A = Y, Yb) ceramics possess good chemical compatibility with the Ag electrode, making them promising candidates for low-temperature cofired ceramics (LTCC) technologies.     

Low‐Temperature Sintering and Microwave Dielectric Properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4–(Ca0.8Sr0.2)TiO3 Composite Ceramics

0.9(Mg_0.95Zn_0.05)₂(Ti_0.8Sn_0.2)O₄–0.1(Ca_0.8Sr_0.2)TiO₃ (MZTS–CST) ceramics were prepared by a conventional solid‐state route. The MZTS–CST ceramics sintered at 1325°C exhibited ε_r = 18.2, Q × f = 49 120 GHz (at 8.1 GHz), and τ_f = 15 ppm/°C. The effects of LiF–Fe₂O₃–V₂O₅ (LFV) addition on the sinterability, phase composition, microstructure, and microwave dielectric properties of MZTS–CST were investigated. Eutectic liquid phases 0.12CaF₂/0.28MgF₂/0.6LiF and MgV₂O₆ were developed, which lowered the sintering temperature of MZTS–CST ceramics from 1325°C to 950°C. X‐ray powder diffraction (XRPD) and energy dispersive spectroscopy (EDS) analysis revealed that MZTS and CST coexisted in the sintered ceramics. Secondary phase Ca₅Mg₄(VO₄)₆ as well as residual liquid phase affected the microwave dielectric properties of MZTS–CST composite ceramics. Typically, the MZTS–CST–5.3LFV composite ceramics sintered at 950°C showed excellent microwave dielectric properties: ε_r = 16.3, Q × f = 30 790 GHz (at 8.3 GHz), and τ_f = ?10 ppm/°C.     

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.