Temperature Coefficient Of Resonant Frequency Research Articles

Temperature Stability of Li2TiO3‐Zn2SiO4 Microwave Dielectric Ceramics

AbstractIn this work, microstructure, composition, and microwave dielectric properties of nominal compositions (1‐x)Li2TiO3‐xZn2SiO4 (x=0.1, 0.2, 0.3, 0.4), which were prepared by conventional solid‐state ceramic route, have been investigated. Li2TiO3 and Zn2SiO4 reacted to form Li2ZnSiO4 and Zn2Ti3O8, where Zn2Ti3O8 is formed during Zn2TiO4 cooling. The microwave dielectric properties of samples are mainly affected by the characteristics and relative content of crystal phase and densification. With the increase of x, the relative dielectric constant (ϵr) decreases gradually. The quality factor (Qf) value increases at first, reaches the maximum value at x=0.2, and then decreases. The temperature coefficient of resonance frequency (τf) value has a sharp decrease due to the increase of Li2ZnSiO4. A near zero τf of about −2.0 ppm/°C was obtained in 0.8Li2TiO3–0.2Zn2SiO4 ceramic sintered at 1150 °C for 4 h with ϵr value of 17.67, Qf value of 19,600 GHz. Thus, it could be a candidate for microwave devices.

Tuning the order-disorder of Zn2–2xLixGa4+xO8 spinel towards high-performance microwave dielectric ceramic

High-Q Zn2–2xLixGa4+xO8 (0 ≤ x ≤ 1) ceramics with spinel structure were synthesized using the traditional solid-state method. Li+ and Ga3+ are introduced into ZnGa2O4 ceramic to tune the order-disorder of the structure. A disordered face-centered cubic phase is achieved in the compositional range of x < 0.9, and an ordered primitive cubic spinel is found as x ≥ 0.9. As x increases, Li+ preferentially occupies the octahedral site, causing partial Ga3+ to occupy the tetrahedron, making a 1:3 (Li: Ga) ordered structure in the octahedral site. A low relative permittivity (εr) of 10.1 and a relatively stable temperature coefficient of resonance frequency (τf) of − 52.3 ppm/°C of Li0.9Zn0.2Ga4.9O8 ceramic (x = 0.9) were attained when sintered at 1300 °C. A maximum quality factor was achieved at x = 0.75 (Li0.75Zn0.5Ga4.75O8) with Q×f = 120,370 GHz (f = 13 GHz). Moreover, the intrinsic influence mechanism of crystal structure on the dielectric properties was explored through the P–V–L chemical bond theory.

Improved microwave dielectric properties of (Mg0.5Ti0.5)3+ Co-substituted Mg2Al4Si5O18 cordierite ceramics

In this work, the Mg2Al4-x(Mg0.5Ti0.5)xSi5O18 (0 ≤ x ≤ 0.20) ceramics were successfully synthesized via the solid-state reaction. The main phase was Mg2Al4Si5O18 with an orthorhombic structure, and the secondary phases (SiO2, TiO2 and Al2SiO5) were formed during the synthesis of Mg2Al4-x(Mg0.5Ti0.5)xSi5O18 ceramics. The substitution of Al3+ by (Mg0.5Ti0.5)3+ occurs complex chemical reaction: Mg ions prefer to occupy the Mg-site deficiency in Mg2Al4Si5O18; Ti ions substitute Si-site at x < 0.12, whereas Ti ions also occupy Al-site and remaining to form TiO2 phase at x ≥ 0.12. The dielectric constant (εr), quality factor (Qf) and temperature coefficient of resonance frequency (τf) are mainly dominated by the ionic polarizability, relative density, secondary phases and bond valence of Mg-site. Additionally, the bond ionicity (fi) of Mg–O, lattice energy (U) of Si–O and bond energy (E) of Al–O also influence εr, Qf and τf, respectively. The moderate (Mg0.5Ti0.5)3+ ions substitution not only effectively improve Qf while maintaining low εr, but also reduce densification temperature. The excellent microwave dielectric properties with εr = 4.45, Qf = 33,995 GHz and τf = −39 ppm/°C were obtained in Mg2Al4-x(Mg0.5Ti0.5)xSi5O18 (x = 0.08) ceramic sintered at 1375 °C, which is potential for millimeter-wave communication.

Enhanced structural and functional performances of Si3N4-reinforced Li2ZnTi3O8 microwave dielectric ceramics

Li2ZnTi3O8 (LZT) ceramics with different amounts of Si3N4 addition were prepared using a traditional solid-state reaction method. The phase structure, sintering behavior, microwave dielectric properties and bending strength of ceramics were studied. Si3N4-doped LZT ceramics had a cubic spinel structure, indicating that a small amount of Si3N4 addition did not undergo the phase transformation of the ceramics. The addition of Si3N4 particles could improve the bending strength and adjust the temperature coefficient of resonant frequency (τf) value of the LZT ceramics. In particular, the LZT ceramics doped with 0.7 wt% Si3N4 sintered at 1025 °C displayed the excellent properties with a bending strength of 202 MPa, an εr of 21.6, a Q×f of 45457 GHz, and a τf of −4.97 ppm/°C.

The structural characteristics and microwave dielectric properties of Ti4+ doped CaMgSi2O6 ceramics

The effect of Ti substitution on microwave dielectric properties and structural characteristics of CaMgSi2O6 ceramics synthesized via solid-state reaction method was investigated by XRD, XPS, Raman spectroscopy, SEM, EDS, Rietveld refinement, P–V-L theory and bond valence theory. XRD patterns indicated that CaTiO3 was gradually formed with the increase in Ti content. The permittivity was closely related to ionic polarizability, which was confirmed by Raman shifts. Quality factor (Q × f) and temperature coefficient of resonant frequency (τf) were considerably affected by lattice stability. Moreover, lattice energy and cation ordering of CaMgSi2O6 influenced Q × f, while cation bond valence affected the τf value. Improved microwave dielectric properties were achieved with high lattice energy and appropriate bond valence for well-densified CaMgSi1.95Ti0.05O6 ceramics with specific values of Q × f = 80774 GHz (±2578 GHz; @13.47 GHz, tan δ = 1.67 × 10−4), εr = 7.94 (±0.208), and τf = −58.56 ppm/°C (±2.65 ppm/°C) with high relative density (ρr = 96.9%).

Structural evolution and microwave dielectric properties of CaTiO3–La(Mg2/3Nb1/3)O3 ceramics

Abstract(1 − x)CaTiO3–xLa(Mg2/3Nb1/3)O3 (CT–LMN; x = 0–1.0) solid solutions were prepared by a solid‐state reaction method. A phase transition from a disordered orthorhombic (Pbnm) structure to a 1:1 ordered monoclinic (P21/n) structure was observed when x increased from 0.5 to 0.6. Some new parameters, such as ionic polarizability in a polyhedron and ionic packing fraction in a polyhedron, were defined to explain the structure–property relationships of CT–LMN ceramics based on the Rietveld refinement results. The measured dielectric constant (εr‐mea) decreased monotonically with B‐site ionic polarizability in the [BO6] octahedron () when the x value increased from 0 to 1.0. The quality factor (Qf) was dominated by the packing fraction of B‐site cations in the [BO6] octahedron (PF[B]), and both presented an increasing trend. The temperature coefficient of resonant frequency (τf) decreased from +588.5 to −79.7 ppm/°C, and it was highly correlated to the tolerance factor (t), and PF[B]. The highest Qf value is obtained at x = 1.0 when sintered at 1600°C for 10 h with εr = 23.65 ± 0.2, Qf = 33517 ± 2000 GHz (@7.8 GHz), and τf = −79.7 ± 2.0 ppm/°C. Moreover, a near‐zero τf value was achieved at x = 0.4 with εr = 43.52 ± 0.2, Qf = 17239 ± 2000 GHz (@5.2 GHz), and τf = −10.2 ± 2.0 ppm/°C.

Sintering characteristics, crystal structure, and microwave dielectric properties of Ce2[Zr1-x(Al1/2Nb1/2)x]3(MoO4)9 ceramics

This work prepared a new type of Ce2[Zr1-x(Al1/2Nb1/2)x]3(MoO4)9 (CZ1-x(AN)xM) (x = 0.02–0.10) microwave dielectric ceramics through the solid-phase process. CZ1-x(AN)xM ceramics exhibited low dielectric constant, ultra-low dielectric loss, and near-zero resonant frequency temperature coefficient, which is suitable for 5 G technology. The effects of (Al1/2Nb1/2)4+ replacing Zr4+ on the sintering characteristics, crystal structure, and microwave dielectric properties of Ce2Zr3(MoO4)9 (CZM) ceramics were studied systematically. In this work, CZ1-x(AN)xM could form a pure crystal structure in the whole doping range according to the X-ray diffraction pattern. The crystal cell parameters of the ceramics were confirmed by Rietveld refinement analysis. Furthermore, the surface morphology of CZ1-x(AN)xM sintered at the optimum sintering temperature was studied by scanning electron microscopy. Some internal parameters of the ceramics were calculated and analyzed by employing the P-V-L theory. The theoretical loss was acquired by employing an infrared reflection spectrometer. When x was 0.04 and the sintering temperature was 850 ℃, the best properties were achieved, including εr = 10.54, Q·f = 91,476 GHz (at 9.55 GHz), and τf = − 8.95 ppm/℃. This work studied the relationship between lattice vibration and microwave dielectric properties and discussed the influence of ion doping on microwave dielectric properties from the perspective of chemical bonds, laying a theoretical foundation for related research.

Improved microwave dielectric properties of MgAl2O4 spinel ceramics through (Li1/3Ti2/3)3+ doping

A series of nominal compositions MgAl2−x (Li1/3Ti2/3) x O4 (x = 0, 0.04, 0.08, 0.12, 0.16, and 0.20) ceramics were successfully prepared via the conventional solid-state reaction route. The phase compositions, microstructures, and microwave dielectric properties were investigated. The results of x-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that a single phase of MgAl2−x (Li1/3Ti2/3) x O4 ceramics with a spinel structure was obtained at x ≤ 0.12, whereas the second phase of MgTi2O5 appeared when x > 0.12. The cell parameters were obtained by XRD refinement. As the x values increased, the unit cell volume kept expanding. This phenomenon could be attributed to the partial substitution of (Li1/3Ti2/3)3+ for Al3+. Results showed that (Li1/3Ti2/3)3+ doping into MgAl2O4 spinel ceramics effectively reduced the sintering temperature and improved the quality factor (Q f) values. Good microwave dielectric properties were achieved for a sample at x = 0.20 sintering at 1500 °C in air for 4 h: dielectric constant ε r = 8.78, temperature coefficient of resonant frequency τ f = −85 ppm/°C, and Q f = 62 300 GHz. The Q f value of the x = 0.20 sample was about 2 times higher than that of pure MgAl2O4 ceramics (31600 GHz). Thus, MgAl2−x (Li1/3Ti2/3) x O4 ceramics with excellent microwave dielectric properties can be applied to 5G communications.

Sintering behavior, microwave dielectric properties, and chemical bond features of novel low-loss monoclinic-structure Ni3(PO4)2 ceramic based on NiO-P2O5 binary phase diagram

Ni3(PO4)2 as microwave dielectrics was investigated in terms of sintering behavior and microwave dielectric properties and synthesized using the solid-state sintering method. X-ray diffraction (XRD) data revealed that the Ni3(PO4)2 ceramics belong to the monoclinic structure with the P21/c (#14) space group. The sintering behavior analysis confirmed that the sample reached a dense state at 1200 °C. It's permittivity (εr) and quality factor (Q × f) possess distinct density-dependent features. The admirable Q × f of 83,430 GHz (at 10.21 GHz) was accomplished coupled with a low εr of 6.23 and temperature coefficient of resonant frequency (τf) of −24.63 ppm/°C in Ni3(PO4)2 ceramic when sintering at 1200 °C for 2 h. Thus, it is a promising candidate for microwave dielectrics with low loss and low permittivity. The dielectric properties were discussed using the chemical bond theory, and their chemical bond features were quantified. The results confirmed the significance of P–O bonds in the microwave dielectric response of Ni3(PO4)2 ceramic.

Influence of the addition of CaTiO3 on the microwave dielectric properties of the BaMoO4 matrix

This work presents the study of the dielectric properties in the microwave region (MW) of BaMoO4 ceramic and composites with CaTiO3 (CTO). The BaMoO4 matrix was synthesized by solid state reaction and characterized by X-ray diffraction. Ceramic composites were obtained by adding 20–80 mol% of CTO in the BaMoO4 matrix. The Silva-Fernandes-Sombra method was used to measure the resonant frequency temperature coefficient (τf), and the BaMoO4 composite with 20% CTO showed an adequate value of relative dielectric permittivity (εr = 8.90), low dielectric loss tangent (tan δ = 9.89.10−4) and τf close to zero (τf = 3.48 ppm °C−1). BMO and its composites were applied as dielectric resonator antennas, and their far-field parameters were obtained through numerical simulation.

AlScN‐on‐SiC Thin Film Micromachined Resonant Transducers Operating in High‐Temperature Environment up to 600 °C

AbstractThe experimental demonstration of aluminum scandium nitride (AlScN)‐on‐cubic silicon carbide (SiC) heterostructure thin film micromachined resonant transducers operating in a high‐temperature environment up to 600 °C is reported. Macroscopic and microscopic vibrations are investigated through a combination of ultrasensitive laser interferometry techniques and Raman spectroscopy. An average linear temperature coefficient of resonance frequency (TCf) of &lt;1 ppm °C−1 within the temperature range from room temperature to 200 °C, and an average linear TCf of −16 ppm °C−1 between 200 and 600 °C, from the fundamental‐mode resonance of AlScN/SiC circular diaphragm resonator with a thickness of 1.9 µm and diameter of 250 µm, is obtained. Higher‐order modes exhibit much larger TCf, which make them strong candidates as high‐temperature‐tolerant temperature sensors or ultraviolet detectors. Raman spectroscopy indicates that the turning points of the peak positions of the longitudinal optical phonon modes of both 3C‐SiC and AlScN occur in almost the same temperature region where the turnover point of TCf is observed, suggesting that the microscopic vibrations in the crystal lattice and the macroscopic oscillation of the diaphragm are naturally mediated by the residual strain inside the materials at varying temperature.

Structure characteristics and enhanced microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–Mg2SiO4 composite ceramics with a tunable τf

The performance of microwave communication devices widely used in 5G network is strongly determined by the properties of dielectric ceramics used in the fabrication, which are required to have a suitable dielectric constant (εr), high Q × f value and near-zero temperature coefficient of resonant frequency (τf). In this work, (1-x)Ba(Mg1/3Nb2/3)O3–xMg2SiO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5) composite ceramics meeting the application requirements have been developed and investigated. Ba(Mg1/3Nb2/3)O3 and Mg2SiO4 could coexist without any unexpected phases due to the different crystal structures and coordination relationship. The sintering behavior and the structural changes of Ba(Mg1/3Nb2/3)O3 were specifically relevant to the microwave dielectric properties. Introducing appropriate Mg2SiO4 content promoted the sintering of Ba(Mg1/3Nb2/3)O3 and the maximum Q × f value of 110,000 GHz was obtained at the sample with x = 0.3 sintered at the optimized temperature of 1420 °C. Due to the low dielectric loss and the opposite sign τf value of Mg2SiO4, the composite ceramic successfully adjusted the τf value to near zero while maintaining a high Q × f value. However, the experimentally measured values of εr and τf were significantly different from the theoretically calculated values due to the “rattling” effect of B-site cations and the enhanced symmetry of oxygen octahedra in Ba(Mg1/3Nb2/3)O3. These structural changes were confirmed by the results of bond valence analysis and Raman vibration spectra. The 0.6Ba(Mg1/3Nb2/3)O3–0.4Mg2SiO4 ceramic sintered at 1420 °C exhibits competitive microwave dielectric properties: εr = 18.9, Q × f = 91,000 GHz (at 8.016 GHz) and τf = 2.6 ppm/°C, which indicates it a promising application prospect of microwave communication.

Microwave dielectric properties and vibrational spectra of (Na0.5xLa1–0.5x)(Nb1−xMox)O4 ceramics with scheelite structures

In this study, (Na0.5xLa1–0.5x)(Nb1−xMox)O4 (0.0 ≤ x ≤ 1.0) ceramics were synthesized by the traditional solid-state reaction method. All the (Na0.5xLa1–0.5x)(Nb1−xMox)O4 samples could be densified well at 1120–1200 °C. Solid solutions with tetragonal scheelite structures were obtained in the (Na0.5xLa1–0.5x)(Nb1−xMox)O4 ceramics when 0.4 ≤ x < 1.0. A temperature-stable microwave dielectric ceramic with a near-zero temperature coefficient of resonant frequency (TCF) of approximately 2.4 ppm/°C was obtained for the (Na0.25La0.75)(Nb0.5Mo0.5)O4 sample, along with a high Q×f value of approximately 45,600 GHz and a low permittivity of approximately 14.5. Introducing the fergusonite phase into the scheelite phase proved effective in obtaining a near-zero TCF.

Structure refinement, defects evolution and calcium doping of Sr2CeO4 microwave dielectric ceramics with high quality factor

Sr2-2xCa2xCeO4 (x = 0, 0.025, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) ceramics were synthesized through cold isostatic pressing and solid-state reaction. The microstructure, defects, microwave dielectric properties, and the effect of Ca2+ doping of Sr2CeO4 ceramics were systematically investigated. As the sintering temperature increased, the densities of Sr2CeO4 ceramics rose, the content of oxygen vacancies increased, and Ce4+ reduction would be enhanced. In addition, the Sr2CeO4 structure had poor compatibility with Ca2+. The major phase could be kept unchanged only when x ≤ 0.1. The reason was that the doping of Ca2+ intensified the distortion of the CeO6 octahedron and induced the structural transformation of the common edges (Sr2CeO4) to the common angles (SrCeO3). With the increase of dopant, the densities of Sr2-2xCa2xCeO4 ceramics increased significantly, while the content of oxygen vacancies also increased. The microwave dielectric properties were mainly influenced by the density, structural symmetry, defects, and the second phase SrCeO3. The dielectric permittivity (εr) of 13.4–15, the quality factor (Qf) of 118,580–52,170 GHz, and the temperature coefficient of resonant frequency (τf) of −58.3 ∼ −47.5 ppm/°C were obtained for Sr2-2xCa2xCeO4 ceramics When x ≤ 0.1. This work has provided a foundation for further research on cerate microwave dielectric ceramics.

Low sintering temperature, temperature-stable scheelite structured Bi[V1−x (Fe1/3W 2/3)x]O4 microwave dielectric ceramics

Low sintering temperature Bi[V1−x(Fe1/3W2/3)x]O4 (BVFWx) (0.02 ≤ x ≤ 0.08) ceramics have been prepared by solid-state reaction. Compositions with 0.02 ≤ x ≤ 0.08 were scheelite-structure, but distortion of [BO4] tetrahedra decreased with increase in x. Although the crystal class remained monoclinic, the phase transition temperature (TC) decreased from 255 ℃ (BV) to 51 ℃ (BVFW0.08), suggesting that higher concentrations of (Fe1/3W2/3) would result in the stabilization of tetragonal scheelite at room temperature. The decrease in the [BO4] distortion additionally resulted in a large reduction in the magnitude of the temperature coefficient of resonant frequency (TCF) with near-zero values obtained by sintering BVFW0.08:2BVFW0.06 at 780 °C to give TCF ≈ −5.9 ppm / °C, relative permittivity εr ≈ 77.4, and microwave quality factor, Q × f ≈ 8100 GHz (@ ~ 4.3 GHz). These promising microwave dielectric properties coupled with the low sintering temperature suggest that BVFWx ceramics are of interest in low-temperature cofired ceramic (LTCC) technology, and for monolithic resonator and filter applications.

Effects of (Cr1/2Nb1/2)4+-substitution on the chemical bond characteristics, and microwave dielectric properties of cerium zirconium molybdate ceramics

A series of Ce2[Zr1−x(Cr1/2Nb1/2)x]3(MoO4)9 (x = 0.02–0.10) ceramics as microwave dielectrics were synthesized and investigated in terms of sintering behaviors, phase compositions, and microwave dielectric properties. The X-ray diffraction data confirmed that the pure phase ceramics were synthesized at 825 °C and all the samples belong to trigonal structure with the R-3c space group. Rietveld refinement was used to achieve the crystal structure parameters by adopting a FULPROF software. The results identified the shrinkage and distortion of [ZrO6] octahedron caused by (Cr1/2Nb1/2)4+ substituted Zr4+. The chemical bond theory was utilized to analyze the relation between chemical bond feature and microwave dielectric properties for understanding the inherent mechanism of the dielectric response. The infrared spectra analysis identified that the spectroscopically determined microwave dielectric loss is consistent with the directly measured, and the inherent loss is mainly derived from the scattering of lattice vibration phonons. Ce2[Zr0.94(Cr1/2Nb1/2)0.06]3(MoO4)9 ceramic obtained at 825 °C for 6 h exhibits considerable properties: relative permittivity (εr) = 10.56, quality factor (Q × f) = 73,224 GHz, and temperature coefficient of resonant frequency (τf) = −7.96 ppm/°C. It indicates that the substitution of (Cr1/2Nb1/2)4+ is an effective way to optimize microwave dielectric materials.

Temperature-compensated BaV2O6-Ba2V2O7 ceramic composite for ULTCC applications

A temperature-compensated dielectric ceramic composite in the BaV2O6-Ba2V2O7 system has been achieved using rule of mixtures and subsequent modulation of composition based on experiments. The BaV2O6 and Ba2V2O7 powders, synthesized by the solid-state route, are mixed in various compositions and sintered between 525 and 600 °C to produce the composites. The effect of sintering temperature and duration on the density, stability of the phases, microstructure and microwave dielectric properties have been investigated. The BaV2O6 and Ba2V2O7 phases coexist up to 575 °C without any reaction, as established by XRD and SEM-EDS analyses. The composite with 0.60 weight (wt) fraction of BaV2O6 sintered to 96% TD at 550 °C and exhibits a temperature coefficient of resonance frequency (τf) very close to zero (+0.2 ppm/K). The relative permittivity (εr = 10.73), loss tangent (tanδ = 3.66 × 10-4), and quality factor (Qu × f = 30,000 GHz) obtained for this composite are adequate for microwave dielectric applications. This composite shows a linear coefficient of thermal expansion of 14 ppm/K. The excellent chemical compatibility with Al during cofiring, makes this composite a suitable choice for ULTCC application.

Microwave hybrid sintering of 0.95(Mg0.95Zn0.05)TiO3-0.05CaTiO3 ceramics and its microwave dielectric properties

Microwave dielectric ceramic powder of 0.95(Mg0.95Zn0.05)TiO3-0.05CaTiO3 (MCT) has been prepared by solid-state reaction method through single-step calcination at 1150 °C. The green bodies prepared from the calcined powder have been sintered by conventional, susceptor-aided, and hybrid microwave sintering techniques followed by annealing. XRD of calcined and sintered ceramics show (Mg,Zn)TiO3 as a major phase with CaTiO3 as a minor secondary phase. Fractographs of fired ceramics obtained by SEM show similar features in conventional and hybrid microwave types of sintering. Microwave dielectric properties such as relative permittivity(εr), temperature coefficient of resonant frequency(τf), and unloaded quality factors (Qu) for conventional sintered at 1325 °C for 4 h are—εr~19.8, τf< –6 ppm/°C and Qu.f 69,600 GHz at 6 GHz. Ceramics obtained through susceptor-aided microwave sintering at 1325 °C for 4 h show poor fired density. But ceramics got by microwave-hybrid sintering (resistive + microwave) at the same temperature show εr~20.6, Qu.f~81,600 GHz at 6 GHz and τf~−6.9 ppm/°C. The effect of hybrid microwave sintering on the dielectric properties of MCT ceramics is found to be more subtle than microstructural.

Effect of Bi2O3–B2O3 as a sintering aid in microstructure and dielectric properties of Fe2Mo3O12 electroceramic

Molybdates from A2Mo3O12 family have been widely investigated due to its low sintering temperature, low thermal expansion coefficient, and low dielectric loss. Fe2Mo3O12 (FMO) is an oxide from this family and widely used in the catalytic field. The aim of this work is to evaluate the influence of the Bi2O3–B2O3 as a sintering aid in the microstructure and dielectric properties of FMO. The diffraction results showed that the FMO with the monoclinic structure phase was obtained after the calcination process (650 °C). Mössbauer spectroscopy showed the formation of Fe2O3 after the sintering process at 800 °C. The scanning electron-microscopic image demonstrates an increase of the grain as a function of sintering aid concentration. The samples were analyzed using the impedance spectroscopy at radiofrequency with temperature variation. The Nyquist diagram obtained in this temperature range was fitted from an equivalent circuit with three R-CPE associations, corresponding to the morphology of the electroceramics. For dielectric properties in the microwave, all the samples showed values of εr lower than 10. Values of Q x f above 14,132.35 GHz were achieved. The thermal stability was evaluated by the temperature coefficient of resonant frequency (τf). The lowest τf values of − 6.55 ppm/°C and − 4.35 ppm/°C (near-zero) were measured to FMO and FMO mixed with 7.5 wt % Bi2O3–B2O3, respectively. Based on these results, FMO can be used to low-permittivity ceramic for low-temperature co-fired ceramics (LTCC) applications, antenna substrate, and millimeter-wave range.

Novel low-εr and lightweight LiBO2 microwave dielectric ceramics with good chemical compatibility with silver

High-speed signal propagation systems require dielectric ceramics with low relative permittivity (εr) and a high-quality factor (Qxf). In this paper, a novel low-permittivity borate ceramic (LiBO2) was synthesized using a conventional solid-state reaction method. Based on the X-ray diffraction and Rietveld refinement, the LiBO2 crystallized into a monoclinic structure with a space group of P21/c. Dense and single-phase ceramic was obtained at 640 °C with comprehensive microwave dielectric properties: a low relative permittivity (εr) of 5.3, a moderate quality factor (Q×f) of 18,200 GHz at 16.3 GHz, and a temperature coefficient of resonant frequency (τf) of − 66.2 ppm/°C. Good chemical compatibility with Ag electrode and thermal expansion coefficient of 25.4 ppm/°C was achieved demonstrating the potential applications as dielectric resonances in wireless communications and substrates in low-temperature cofired ceramics.