Temperature Coefficient Of Resonant Frequency Research Articles

Processing strategy and composite regulation on dielectric performance in Li2O–Al2O3–B2O3 dielectric systems using SrTiO3

AbstractIn this paper, we investigated the effect of processing parameters and composite regulation on the structure and property relationship of lightweight low‐permittivity Li2O–Al2O3–B2O3 dielectric system. Li2BAlO4 ceramic and (1 − x)Li2BAlO4–xSrTiO3 ceramics were synthesized using a conventional solid‐state reaction method. Thermodynamic analysis, sintering temperature, phase formation, crystal structure, and microwave dielectric properties were investigated. Thermal analysis revealed a melting temperature of 847°C, suggesting a comparatively low temperature for the sintering of Li2BAlO4 ceramics. Li2BAlO4 crystalized into a monoclinic structure with P21/c space group, with [Al2B2O8] rings connected by [BO3] triangles and [AlO4] tetrahedra through Al–O–Al bridges. Dense Li2BAlO4 ceramics with a relative density of ∼97.7% were sintered at 750°C and had optimal microwave dielectric properties with relative permittivity (εr) of 5.13, quality factor (Q × f) of 22 610 GHz, and the temperature coefficient of resonance frequency (τf) of −112.5 ppm/°C. The 0.88Li2BAlO4–0.12SrTiO3 composite ceramic has excellent microwave dielectric properties with εr = 8.83, Q × f = 14 000 GHz, τf = 4.6 ppm/°C. The ceramics also demonstrated an inert behavior with silver electrodes proving its application in low‐temperature cofired ceramic (LTCC) technology.

Strontium tantalate ceramics for dielectric resonator and antenna applications

Bulk SrTa2O6 ceramics were produced via solid-state reactive sintering, characterized by x-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, and their dielectric properties determined via resonant cavity in the 5G frequency domain. Two polymorphs were obtained. Orthogonal β phase ceramics, obtaining much lower relative densities, achieved, at ∼5 GHz, an effective permittivity (εeff) of ∼22, dielectric losses (tanδ) around 1 × 10−2 and temperature coefficient of resonant frequency (τf) of around 250 ppm/°. Tetragonal tungsten bronze β’ phase ceramics achieved relative densities of ∼87%, and at ∼2.8 GHz a higher εeff between 79-85, lower ‘tanδ’ around 5 × 10−3, and a ‘τf’ of about 300 ppm/° at 90°C. Both phases are found to be Sr-deficient, which may have caused a liquid-phase sintering in the powder bed configuration used for these ceramics. The performance of a prototype dielectric resonator antenna incorporating a β’ ceramic was demonstrated to validate the measured dielectric properties.

Influence of TiO2 addition on the Mg4Nb2O9 ceramic phase and its application in the radiofrequency region

In this work, the dielectric properties of (1-x) Mg4Nb2O9 – (x) TiO2 composite ceramics in radiofrequency and the microwave region were evaluated. X-ray diffraction demonstrated that Mg4Nb2O9 (MNO) reacted with TiO2 resulting in the formation of new crystalline phase Mg5(Nb0.625Ti0.375)4O15. Complex Impedance Spectroscopy (CIS) analysis was realized to analysis the electrical properties of materials, whereas was observed that activation energy (Ea) decrease from 1.64 to 1.37 eV with an increase in TiO2 concentration. Temperature capacitance coefficient (TCC) was obtained and showed that at different frequencies all materials could be used as Class 1 ceramic capacitors according to EIA RS-198. In the Microwave region, MNO – TiO2 demonstrated ε’r between 12.07 (MNO) and 14.08 (MNO18T), tan δ values varying of 2.64 × 10-4 (MNO) up to 5.92 × 10−4 (MNOT14). Regarding the temperature coefficient of resonant frequency (τf) was observed that the values decreased with the increase in TiO2, with the value closest to zero being that of pure MNO (τf = −27 ppm.°C−1). The results presented show that materials evaluated could be utilized in devices that can be act in radio frequency (RF) and microwave (MW) regions.

Zero-Temperature Coefficient of Resonant Frequency in [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-Ca0.6(La0.9Y0.1)0.2667TiO3 Ultra-Low-Loss Composite Dielectrics

Investigating the microwave dielectric properties of ceramics prepared through the conventional solid-state route, such as x[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-(1−x)Ca0.6(La0.9Y0.1)0.2667TiO3, reveals notable characteristics. [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 shows a permittivity (εr) of approximately 20, a high quality factor (Q × f) ranging between 250,000 and 560,000 GHz, and a temperature coefficient of resonant frequency (τf) of approximately −65 ppm/°C. To enhance the temperature stability, Ca0.6(La0.9Y0.1)0.2667TiO3 featuring a τf value of +374 ppm/°C was incorporated into the [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 composition. τf demonstrated an increase with rising Ca0.6(La0.9Y0.1)0.2667TiO3 content, reaching zero at x = 0.95. A ceramic composition of 0.95[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-0.05Ca0.6(La0.9Y0.1)0.2667TiO3, incorporating 3wt.% BaCu(B2O5) as sintering aids, exhibited outstanding microwave dielectric properties: εr~22.5, Q × f~195,000 (at 9 GHz), and τf~0.1ppm/°C, with a sintering temperature at 950 °C. This material is proposed as a prospective candidate for 6G band components and GPS antennas.

Bond theory, vibrational spectroscopy, and dielectric responses of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics

This study established the connection between structure and dielectric responses by synergistically evaluating the chemical bond characteristics and lattice vibrational spectroscopies of trirutile ATa2O6 (A = Mg, Ni) microwave ceramics. The MgTa2O6 ceramic exhibits a uniform grain size distribution and a dense microstructure, with dielectric characteristics at microwave range of a εr value of 27.27, a high Q×f value of 109,203 GHz (8.73 GHz), and a τf of approximately 53.38 ppm/°C when sintered at 1300 °C, while the NiTa2O6 ceramic presents a smaller average grain size and minor micropores, with dielectric characteristics at microwave range of εr = 24.58, Q×f = 27,610 GHz (9.25 GHz), and τf = 33.94 ppm/°C, sintered at 1250 °C. The structural refinement and atomic arrangements confirm a trirutile structure along the [001], [100], and [3 3‾1‾] zone axes. Ta–O bonds are found to contribute the most to the ionic character of a bond, bond susceptibility, lattice stability, thermal expansion behaviors, and strength of bonding ability, indicating their significant influence on dielectric polarization, lattice stability, and temperature coefficient of resonant frequency. Raman scattering spectra analysis reveals that the A1g mode near 700 cm−1 mainly controls the Raman vibrational behaviors. The theoretical dielectric properties calculated from the infrared spectrum and dielectric properties analysis consistent with the measured dielectric performances, suggesting that the dielectric characteristics at the microwave range are mainly determined by the oscillatory absorption of structural phonons, with the first two modes at 210.48 cm−1 and 232.87 cm−1 contributing 72.02% to the εr value and 90.45% to the tanδ value, respectively.

Effect of raw material pretreatment and ionic radius on the preparation and microwave dielectric properties of Re2TiO5 ceramics

The present study focuses on the synthesis and characterization of rare-earth titanates, specifically Re2TiO5 (ReLa, Nd, Sm), with a particular emphasis on their microwave dielectric properties. The factors influencing the synthesis of La2TiO5 compound through the traditional solid-state method were thoroughly investigated, with a significant finding being the notable impact of moisture absorption in La2O3. The impact of variations in rare-earth cation radii on the structure and dielectric properties was systematically analyzed. Re2TiO5 (ReLa, Nd, Sm) ceramics crystallized into an orthorhombic structure with space group Pnam, which was confirmed through Rietveld refinement. The resulting materials demonstrated exceptional microwave dielectric properties characterized by a low permittivity range of 13.72–17.39, high-quality factors ranging from 8331 to 17,795 GHz, and a significantly reduced temperature coefficient of resonance frequency (−33.2∼-12.6 ppm/°C). The correlation between microwave dielectric properties and structural characteristics (including ionic polarizability, packing fraction, and bond valence) was investigated. The exceptional potential of these rare-earth titanates lies in their ability to meet the stringent requirements for low signal transmission delay in wireless communication systems, owing to their advantageous low permittivity within the microwave frequency spectrum.

Phase evolution and enhanced Q×f in BaSi2O5 ceramics with Co2O3 substitution

According to the chemical formula Ba1-xCoxSi2O5, low permittivity ceramics were prepared using BaCO3, Co2O3 and SiO2. Orthorhombic structured BaSi2O5 limited solid solution was obtained at x≤0.1. It coexisted with BaCo2Si2O7 and SiO2 in the range of 0.3≤x≤0.5. While x=0.7, the three-phase equilibrium was destroyed, accompanied by BaSi2O5 vanishing. At x=1, all Si existed in the form of Co2SiO4 and SiO2. Co2O3 melting decreased the sintering temperature from 1200 °C to 1025 °C. Because of the dielectric polarizability decrease, Co introduction brought in low dielectric constant εr. Notably, the quality factor Q×f was boosted to 60,340 GHz, which was almost 4 times than the original (∼16,526 GHz). This occurred because the intrinsic loss and extrinsic loss were significantly reduced by the average bond covalence increase and SiO2 generation (Q×f∼80,400 GHz), respectively. The variation of resonant frequency temperature coefficient τf was explained from the view of the change in the bond valence of oxygen. When x=0.5, the system with a high relative density of 98.63% exhibited superior microwave dielectric properties: εr=6.77, Q×f=60,340 GHz, and τf=-47.11 ppm/°C.

Dielectric properties of La2MoO6 ceramics at microwave frequency for application in wireless sensors

The microwave dielectric properties of La2MoO6 ceramics were investigated in preparation for their application in mobile communication. La2MoO6 ceramics were prepared by the conventional solid-state method under varied sintering conditions. The X-ray diffraction peaks of La2MoO6 ceramic did not vary significantly with sintering conditions. The average grain size of La2MoO6 ceramics increased with increasing the sintering temperature and duration. The maximum density of 5.67 g/cm3, the dielectric constant ( ε r ) of 14.1, the quality factor (Q × f) of 68,000 GHz, and the temperature coefficient of resonant frequency ( τ f ) of −56 ppm/°C had been attained when La2MoO6 ceramics that sintered at 1300 °C for 4h.

Sintering behavior, crystal structure, and microwave dielectric properties of a novel NaY9Si6O26 ceramic

AbstractThis study investigates NaY9Si6O26 ceramics prepared through the solid‐phase method, focusing on their microwave dielectric properties and crystallographic characteristics. X‐ray diffraction analysis reveals a hexagonal crystal structure for NaY9Si6O26 ceramics within the P63/m (176) space group. Rietveld refinement analysis precisely determines the lattice constants as a = b = 9.3423 Å, c = 6.7524 Å, and a unit cell volume of V = 510.3877 Å3. Additionally, Raman spectroscopy unveils a noteworthy correlation between the quality factor and the full width at half maximum of the A1g(O) mode at 878 cm−1. The structural attributes, including lattice fringes and diffraction patterns of hexagonal NaY9Si6O26 ceramics, are elucidated through transmission electron microscopy. Of significance are the microwave dielectric properties of NaY9Si6O26 ceramics sintered at 1465°C, revealing a relative permittivity (εr) of 10.42, an impressive Q × f product of 33 766 GHz (at f = 11.14 GHz), and a temperature coefficient of resonant frequency (τf) of −28.7 ppm/°C. This comprehensive investigation contributes to the understanding of both the structural and microwave dielectric characteristics of NaY9Si6O26 ceramics, with potential applications in advanced electronic devices.

Sintering behaviors and microwave dielectric properties of Ba3P4O13 ceramics

In this study, a Ba3P4O13 ceramic was synthesized adopting a conventional solid-state ceramic method. Optimal microwave dielectric properties were obtained in ceramic samples sintered at 840 °C for 4 h with a εr (permittivity) = 7.9, a Q × f (Q = 1/dielectric loss, f = resonant frequency) = 14,200 GHz (at 11.18 GHz), and a τf (TCF, temperature coefficient of resonant frequency) = + 48 ppm/°C. τf value shifted from + 45 ppm/°C to ‒ 31.5 ppm/°C with sintering temperature rising from 860 °C to 900 °C, and this decrease in τf value was mainly caused by the decomposition of Ba3P4O13 into BaP2O6 and Ba2P2O7. Furthermore, a ceramic sample sintered at 890 °C achieved a near zero τf (− 1.3 ppm/°C), together with a εr = 7.7 and a Q × f = 13,000 GHz (at 11.44 GHz). Ba3P4O13 ceramic has demonstrated potential as a material suitable for low-temperature co-fired ceramic technology (LTCC).

Acceleration of optimizing the dielectric properties of (Ca0.7Nd0.2)1−x(Li0.5Nd0.5)xTi1−y(Mg1/3Nb2/3)yO3 with the aid of machine learning

AbstractThe three key properties required for microwave dielectric ceramics are suitable dielectric constant (εr), high quality factor (Q × f), and near‐zero temperature coefficient of resonant frequency (τf). Due to the intricate coupling relationship among these three properties, regulating one often leads to the deterioration of the remaining two. In this study, the synergetic regulation of dielectric properties of Ca0.7Nd0.2TiO3 was investigated to reduce τf to near‐zero while maintaining its high εr by A‐ and B‐site substitutions. To avoid the seesaw effect and improve the efficiency of composition optimization, machine learning method was introduced in this study. First, the models for predicting dielectric properties were fitted based on a small amount of high‐quality data gathered via a uniform experimental design. Then the dielectric properties of 1037 compositions of (Ca0.7Nd0.2)1−x(Li0.5Nd0.5)xTi1−y(Mg1/3Nb2/3)yO3 were predicted, from which 69 microwave dielectric ceramics with near‐zero τf and adjustable εr of 95–125 were quickly picked out, and 5 of them were proved by experiments with very high prediction accuracy. This work was finished within a period of 1 month, which proves the obvious acceleration of composition designing process of microwave dielectric ceramics with the aid of machine learning.

Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity (εr) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics, as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr4+ and Hf4+ substituted Ba4Sm9.33Ti18O54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency (τf) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm2Ti2O7 second phase with a large positive τf. Optimal microwave dielectric properties of εr = 81.3, Q × f = 10,800 GHz, and τf = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies (VO∙∙). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr4+ and Hf4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.

Spinel-trirutile microwave dielectric ceramics with high Q and excellent temperature stability based on MgO-Al2O3-Ta2O5 ternary systems

(1-x)MgAl2O4-xMgTa2O6 composite ceramics based on the MgO-Al2O3-Ta2O5 pseudoternary phase diagram were prepared by the solid-state reaction. MgAl2O4 and MgTa2O6 could coexist due to their different crystal structures. MgAl2O4 inhibited the rapid growth of MgTa2O6 grains, and dense microstructures (ρ > 95%) with a uniform grain size distribution was obtained, with an optimal densification temperature of 1550 - 1575 °C. The temperature coefficient of resonant frequency (τf) and quality factor (Q×f) were optimized by introducing MgTa2O6 phases with low dielectric loss and positive τf. In addition, the partial solid solutions of Al3+ into Ta5+ sites resulted in loosening bonds within [Al/TaO6] octahedra and abnormally large polarizabilities, which was confirmed by the decrease in VTa-O and the redshift of A1 g(Ta-O) mode. Consequently, the relative permittivity (εr) and τf values of MgAl2O4-MgTa2O6 composite ceramics were further enhanced, exceeding the predicted ones. The 0.6MgAl2O4-0.4MgTa2O6 composition sintered at 1550 °C achieved excellent performance, with a near-zero τf value of 3.3 ± 1.7 ppm/°C, a low εr of 16.4 ± 0.3 and an ultra-high Q×f of 179,000 ± 6700 GHz @ 8.94 ± 0.04 GHz. These findings hold promising applications in the field of 5 G/6 G high-frequency communication.

Ilmenite-type structure and pervoskite structure mix-phase ceramics at microwave frequency

ABSTRACT The impact of CuB2O4 additive used as a sintering aid on the microstructures and microwave dielectric characteristics of mixed phase (Mg0.95Zn0.05)Co0.05TiO3-Ca0.6(La0.9Y0.1)0.2667TiO3 ceramics was investigated. CuB2O4 additives can effectively lower the densification temperature of (Mg0.95Zn0.05)Co0.05TiO3-Ca0.6(La0.9Y0.1)0.2667TiO3 from 1450°C to the range of 1050°C ~ 1175°C. Doping CuB2O4 (0.25 ~ 2 wt%) in 0.875(Mg0.95Zn0.05)Co0.05TiO3-0.125Ca0.6(La0.9Y0.1)0.2667TiO3 ceramics can substantially enhance their microwave dielectric properties and density. With the addition of 1% and 0.25% CuB2O4, Q × f values of 43,000 GHz and 7700 GHz were obtained at 1050–1175°C, respectively. Different additions of CuB2O4 have a significant effect on the Q × f value. Temperature coefficient of resonant frequency of 0.875(Mg0.95Zn0.05)Co0.05TiO3-0.125Ca0.6(La0.9Y0.1)0.2667TiO3 (0.875MZCT–0.125CLYT) varied from 16 to 30.9 ppm/°C when adding different CuB2O4 (0.25 ~ 2 wt%).

Re2TiO5: Special dielectric titanates exhibiting abnormally low permittivity and a positive coefficient of resonance frequency

AbstractIn this study, a series of rare‐earth titanates with the general formula Re2TiO5 (Re = Er, Tm, Yb, and Lu) were synthesized and their microwave dielectric properties were reported. The impact of differences in rare‐earth cation radii on the structure and dielectric properties was systematically analyzed. The findings indicated that ceramics of Re2TiO5 (Re = Er, Tm, Yb, and Lu) were crystallized into a cubic structure with space group Fd‐3m, as confirmed by Rietveld refinement and selected‐area electron diffraction patterns. The rare‐earth elements were analyzed for their impact on microwave dielectric properties, considering factors such as ionic polarizability, packing fraction, and bond valence theory. The resulting materials exhibited excellent microwave dielectric properties with a low permittivity (6.95–7.21), high‐quality factors (19 451–20 115 GHz), and low positive temperature coefficient of resonance frequency (19.34–20.90 ppm/°C). The origin of low permittivity was elucidated through the analysis of bond length, X‐ray photoelectron spectroscopy, and impedance spectroscopy. This series of titanates exhibited unusually low permittivity characteristics in the microwave frequency range, which could meet the low signal transmission delay requirements in wireless communication.

Crystal structure and microwave dielectric properties of A- and B-site co-substituted NdNbO4 ceramics

The microwave dielectric properties of NdNbO4 (NN) ceramics were optimized by substituting Ca2+ at the A-site and W6+ at the B-site. (1-x)NdNbO4-xCaWO4 (NNCWx) (x = 0–0.3) ceramics crystallize in the monoclinic fergusonite structure (space group I2/a), whereas NNCW-0.4 exhibits a tetragonal scheelite structure (space group I41/a), suggesting that Ca2+/W6+ doping effectively contributed to the ferroelastic phase transition. A near-zero temperature coefficient of resonant frequency (τf) of +7.8 ppm/°C, a high Q×f value of 59,190 GHz, and a low permittivity (εr) of 17.51 were obtained for the NNCW-0.3 ceramic. With the increase of x, the permittivity decreases gradually, while τf shows the opposite trend. The permittivity is mainly affected by the polarizability per unit molar volume (α/Vm) and the rattling effect of A-site cations (Nd3+ and Ca2+). The Q×f values of NNCWx ceramics are mainly affected by relative density, packing fraction, and lattice energy (U). The influencing mechanism of τf is a combination of an increase in the temperature coefficient of ion polarizability (ταm), lattice strain, and phase transition.

High-Q, temperature-stable, and medium-permittivity composite ceramics of tungstenbronze-type and perovskite titanates through layer-stacking process

High-Q and temperature-stable ceramics are indispensable in microwave engineering. However, medium-permittivity (εr ∼ 60, named as K60) microwave dielectric ceramics that meet the above demands are yet to be synthesized. High-Q Ba4Sm9.33Ti16.5Al2O54 (BSTA) and Ca0.6Sm0.27Ti0.8Al0.27O3 (CSTA) ceramics have large resonant frequency temperature coefficients (τf) with opposite signs. The composites of the two are expected to have good dielectric properties, but there will be obvious diffusion when they are compounded with each other by sintering after directly mixing the raw powder, which would lead to severe deterioration in dielectric properties. In this work, the undesired diffusion can be effectively avoided by stacking two or three ceramic layers together, which are achieved by two methods named adhesive bonding and spark-plasma-sintering (SPS) cofiring. The finite element method (FEM) analysis with COMSOL Multiphysics proposed in this work can precisely predict the microwave dielectric properties of layered ceramics, helping to determine the ratio of different layers to reach near-zero τf. The adhesive-bonded layered ceramics exhibit excellent dielectric properties: εr = 62.2, Q×f = 21,400 GHz, and τf = –0.7 ppm/°C. The SPS-cofired layered ceramics can be fabricated in one time, partially solving the problem of sintering mismatch between different layers, together with superior properties of εr = 59.8, Q×f = 19,780 GHz, and τf = –0.6 ppm/°C. These layered ceramics could fill the gap of high-Q and temperature-stable K60 microwave dielectric ceramics. The layer-stacking process and related FEM simulations can be used to design more high-Q and temperature-stable microwave dielectric ceramics and devices.

Improvement of τf in HfTiO4 microwave dielectric ceramics with Zr‐ and Sn‐substitution

Abstract(Hf1‐xZrx)TiO4 and (Hf1‐xSnx)TiO4 ceramics were prepared through a standard solid‐state reaction route, and the microwave dielectric characteristics were determined together with the microstructures. The single‐phase solid solution in space group Pbcn was obtained in (Hf1‐xZrx)TiO4, while the two‐phase structure with (HfTiO4(s.s.) major phase in space group Pbcn and Sn0.3Ti0.7O2 secondary phase in space group P42/mnm) was determined in (Hf1‐xSnx)TiO4. The temperature coefficient of resonant frequency τf could be significantly improved to near‐zero in both systems, and the best combination of microwave dielectric characteristic was achieved at x = 0.5 in (Hf1‐xZrx)TiO4: εr = 39.0, Qf = 43,150 GHz at 5.3 GHz and τf = 3 ppm/°C, and at x = 0.225 in (Hf1‐xSnx)TiO4: εr = 37.2, Qf = 52,600 GHz at 5.5 GHz and τf = ‐6 ppm/°C. In the solid solutions, the obvious improvement of τf could be deeply linked with the degree of covalency and the restoring forces of structure. While, the intermediate near‐zero τf is achieved by mixing the phases with opposite τf in multiphase materials. The present work provided an effective way to modify the temperature coefficient of resonant frequency in microwave dielectric ceramics.

Effects of ion occupancy and polarizability on the crystal structure and microwave dielectric properties of CaEuCO4 (C[dbnd]Ga, Al) ceramics

CaEuCO4 (CGa, Al) microwave dielectric ceramics were produced through a solid-state reaction. Orthorhombic olivine CaEuGaO4 (pnma) exhibits a lower permittivity (εr = 9.7), a higher quality factor (Q × f = 82,049 GHz), and a larger negative resonant frequency temperature coefficient (τf = −54.6 ppm/°C). CaEuAlO4, which has a similar chemical formula, exhibits a perovskite-like structure (I4/mmm, K2NiF4-type), and its microwave dielectric properties are εr = 18.9, Q × f = 43,132 GHz, and τf = −1.6 ppm/°C. The difference in their structures is mainly caused by the properties of the Ga (III) atom. The difference in their dielectric properties can be proved to be affected by the “rattling” effect of Eu3+ through the bond valence theory. The relationship between the covalence (fc) and the bond strength (S) was investigated, and the higher bond strength might be the main reason for the higher Q × f in CaEuGaO4 ceramic.

Low‐k dielectric materials derived from ZSM‐5 zeolite

AbstractLow‐k dielectric materials were prepared by sintering ZSM‐5 zeolite powder compacts at temperatures ranged 1200–1300°C, and the microwave dielectric characteristics were investigated together with the structure evolution during sintering. It was failed to obtain ZSM‐5 ceramics by high temperature sintering because the densification could never occur below the tolerable temperature and the ordered porous structure completely collapsed above the tolerable temperature. The structure changed from ZSM‐5 zeolite to SiO2‐Al2O3 glass at 1240°C, and finally to SiO2‐based cristobalite ceramics above 1275°C. A low dielectric constant (2.63‐2.78) combined with low dielectric loss (< 0.0005 at 18 GHz) and small temperature coefficient of resonant frequency (varied from ‐18.6 to ‐8.1 ppm/°C) was achieved in the present materials, and the value of dielectric loss was the lowest one achieved so far in the dielectric materials with a dielectric constant lower than 3. With the structure evolution from ZSM‐5 zeolite to SiO2‐Al2O3 glass and finally to SiO2‐based cristobalite ceramics, the dielectric constant increased from 2.27 to 2.78, while the Qf value indicated a complicated variation tendency, and the higher Qf values were achieved in the amorphous and crystalline states, while significant drop was determined in the partial amorphous state. It should be a great challenge to prepare dense zeolite ceramics without collapse of ordered porous structure, and then the ultra‐low dielectric constant materials with high Q could be expected.