Temperature Coefficient Of Resonant Frequency Research Articles

Synthesis of LiBGeO4 using compositional design and its dielectric behaviors at RF and microwave frequencies

Borates are promising candidates as dielectric substrate materials in low temperature cofired ceramics technology (LTCC) due to their relative low sintering temperatures and relative permittivities compared to their counterparts. However, synthesizing borates having single-phase is still challenging because of the volatility and hydrophilicity of boron resources. In this work, a compositional design was utilized to synthesize single-phase LiBGeO4 ceramics over a broad temperature range from 600 to 840 °C. Radio-frequency dielectric behaviours featured a strong temperature dependence, especially at high temperatures (>400 °C), which is related to the thermally activated polarizations. LiBGeO4 ceramic sintered at 820 °C has optimum microwave dielectric properties with the relative permittivity (εr) of 6.28, a quality factor (Q × f) of 21,620 GHz, and a temperature coefficient of resonance frequency (τf) of -88.7 ppm/°C. LiBGeO4 also showed chemical inertness when cofired with silver (Ag), provided an evidence for its utilization in LTCC technology. Overall, this work provides a strategy for facile synthesis of phase pure borates, via the proposed two-step process to obtain stable boron resources.

Influence of substituting Na+ for Mg2+ on the crystal structure and microwave dielectric properties of Mg1-xNa2xWO4 ceramics

The Mg1-xNa2xWO4 (0 ≤ x ≤ 0.14) microwave dielectric ceramics were prepared through traditional solid-state reaction and sintered at 875−925 °C for 4 h. Compared with pure MgWO4 ceramic, the samples with substituting Na+ for Mg2+ could be sintered at a lower temperature, the quality factor values and the densification of microstructure were obviously improved. Raman spectroscopy proved that the relative permittivity was related to the multiple phases and molecular polarizability. In addition, the distortion of[MgO6] octahedron also changed, resulting in resonance frequency temperature coefficient varied nonlinearly from x = 0 to 0.14. Considering the applications of low temperature co-fired ceramics technology, the Mg1-xNa2xWO4 (x = 0.06) ceramic sintered at 875 °C had the best performance. Not only did it have excellent microwave dielectric properties of εr = 10.474, Q × f = 45,868 GHz, and τf = −69 ppm /ºC, but also presented great chemical compatibility with the commonly used Ag electrode.

Improvement in thermal stability of resonance frequency of LiCa3MgV3O12 ceramics through compositional modulation

Impacts of Ba replacement for ca. on the sintering behavior, phase constitution, and microwave dielectric properties of LiCa3MgV3O12 ceramics were investigated. A series of LiCa3 − xBaxMgV3O12 (x = 0.1, 0.2, and 0.3) ceramics were well densified using a solid-state reaction method at temperatures lower than 960 °C. Strong dependence on the composition and sintering temperature was found for the crystal structure and microwave dielectric properties. A limited solid solution was formed up to x = 0.1, beyond which a secondary phase, Ba3(VO4)2, was induced by Ba substitution. The relative permittivity increased, while the quality factor showed a downward tendency with increasing Ba substitution. Especially, the temperature coefficient of resonance frequency shifted to the positive side and a low τf value of − 17.8 ppm/°C was obtained at x = 0.3 along with a relative permittivity of 11.8 and a quality factor of 21,100 GHz.

A novel low sintering temperature scheelite-structured CaBiVMoO8 microwave dielectric ceramics

Abstract Novel medium-permittivity scheelite-structured CaBiVMoO8 ceramics were prepared by a solid-state reaction route. The effects of sintering temperature on the phase composition, microstructure and microwave dielectric properties of CaBiVMoO8 ceramics were investigated systematically. The Rietveld refinements of X-ray data revealed all samples were well crystallized in space group I41/a. All the samples exhibited a closely packed grain morphology and discernable grain boundaries. The relationship between microwave dielectric properties and bulk density of samples at different sintering temperatures was further researched. Besides, the lattice energy was one of the important factors affecting the Q×f values of CaBiVMoO8 ceramics. The temperature coefficient of resonant frequency (τf) could be slightly affected by sintering temperature. The CaBiVMoO8 ceramics were expected to be applied to low temperature co-fired ceramics technology. In this paper, the CaBiVMoO8 ceramics exhibited excellent properties sintered at 850 °C for 4h: er ∼ 40.55, Q×f ∼ 16,670 GHz, τf ∼ +55.90 ppm/°C.

Effect of synthesis and sintering technique on the long-range 1:3 cation ordering and microwave dielectric loss of Li2ZnTi3O8 ceramics

This study first reports the synthesis of Li2ZnTi3O8 (LZTO) system by microwave (MW) and conventional (CS) sintering techniques. The effects of both synthesis and sintering technique on the structure, degree of ordering and microwave dielectric properties of LZTO ceramics were investigated. Based on XRD data analysis, a single phase Li2ZnTi3O8 is obtained for both synthesis techniques. However, fully ordered LZTO system can only be obtained by the CS method. All the samples display nearly non-homogenous grain growth with an average grain size of 7 μm (MW sintering) and 38 μm (CS sintering), respectively. The calculated activation energy of the grain growth for LZTO ceramics was reduced from 329 kJ/mol (MW process) to 233 kJ/mol (CS process). The LZTO ceramics finally densified at 1075 °C display dielectric constants of εrCS = 25.26 and εrMW = 25.65, temperature coefficient of resonant frequencies of τfCS = -13.6 ppm/°C and τfMW = -12.0 ppm/°C and Q×f values of 76,000 GHz and 65,000 GHz for CS and MW samples, respectively. It is clear, therefore, that the synthesis and thermodynamics (sintering) can both play an important role in shaping the physical properties of LZTO materials.

A3Y2Ge3O12 (A = Ca, Mg): Two novel microwave dielectric ceramics with contrasting τf and Q × f

Two garnet-structured microwave dielectric ceramics of A3Y2Ge3O12 (A = Ca, Mg; called CYG and MYG, respectively) were synthesized. CYG was crystallized in a normal cubic garnet structure with Ca2+ fully occupying the dodecahedral (A) site, whereas MYG was an inverse garnet with mixed distribution of Mg2+/Y3+ at the A site. The difference in ionic occupation resulted in anomalies in microwave dielectric properties, with dielectric constant (εr) = 14.1, quality factor (Q × f) = 12,600 GHz and positive temperature coefficient of resonant frequency (τf) =120.5 ppm/°C for MYG ceramic and εr = 10.8, Q × f = 97,126 GHz and τf = −40.6 ppm/°C for CYG ceramic. The large deviations in measured εr from theoretical εth possibly resulted from the garnet structural constraints leading to ‘rattling’ Mg2+ and Y3+ in A site of MYG. Infrared reflectivity spectra analysis revealed ion polarization contributed mostly to the permittivity of both ceramics in microwave frequency ranges.

Microwave dielectric properties, microstructure, and bond energy of Zn3-xCoxB2O6 low temperature fired ceramics

Low temperature co-fired ceramics (LTCCs) technology plays an important role in modern wireless communication. Zn3-xCoxB2O6 (x = 0–0.25) low temperature fired ceramics were synthesized via traditional solid-state reaction method. Influences of Co2+ substitution on crystal phase composition, grain size, grain morphology, microwave dielectric properties, bond energy, and bond valence were investigated in detail. X-ray diffraction analysis indicated that the major phase of the ceramics was monoclinic Zn3(BO3)2. Solid solution was formed with Co2+ substituted for Zn2+ because no individual phase that contained Co was observed. An increase in the amount of Co2+ substitution changed average grain sizes, and regrowth of grains were observed with Co2+ substitution. Appropriate amount of Co2+ substitution improved densification. With changes in Co2+ substitution, bond energy of major phase and average bond valence of B–O were positively correlated to temperature coefficient of resonant frequency. The Zn2.927Co0.075B2O6 ceramic sintered at 875 °C for 4 h exhibited excellent microwave properties with εr = 6.79, Q × f = 140,402 GHz, and τf = −87.42 ppm/°C. This ceramic is regarded as candidate for LTCC applications.

Crystal structure, lattice energy and microwave dielectric properties of melilite-type Ba1-Sr Cu2Si2O7 solid solutions

Abstract Ba1-xSrxCu2Si2O7 solid solutions with melilite-type structure were synthesized by solid-state reaction method. The Rietveld refinement, P-V-L theory and impedance spectroscopy were carried out for Ba1-xSrxCu2Si2O7 to investigate the correlations between the crystal structure and microwave dielectric properties. Single BaCu2Si2O7 phase with orthorhombic structure (Pnma) was obtained in the range of 0–0.35. The corrected dielectric constant (er-corr) showed a monotonously decreasing trend with the x value, which was caused by decreasing of total bond susceptibility (Σχμ) and ionic polarizability of primitive unit cell ( α D T /Vm). The variation of Q×f value was closely correlated to the total lattice energy (Ucal) and activation energy (Ea) of Ba1-xSrxCu2Si2O7. The Q×f value increased linearly until reaching the maximum value (51515 GHz) at x = 0.20 and then decreased. The temperature coefficient of resonant frequency (τf) presented an opposite trend with the Q×f value and it was dominated by the lattice energy (ΣU(Cu-O)) and the susceptibility of Cu-O bond (χ(Cu-O)). Moreover, excellent microwave dielectric properties were achieved at x = 0.20 with er = 8.43, Q×f = 51515 GHz and τf = −29.70 ppm/°C.

Direct Integration of Cold Sintered, Temperature-Stable Bi2Mo2O9-K2MoO4 Ceramics on Printed Circuit Boards for Satellite Navigation Antennas

Bi2Mo2O9-K2MoO4 (BMO-KMO) composite ceramics with >95% theoretical density were densified by cold sintering at 150 °C. XRD, Raman, back-scattered SEM and EDX spectroscopy indicated that the BMO and KMO phases coexisted in all composites without inter-diffusion and secondary phases. Temperature coefficient of resonant frequency with near-zero value ∼ -1 ppm/°C was acheived for BMO-10%KMO with pemittivity ∼ 31 and quality factor ∼ 3,000 GHz. Cold-sintered composite ceramics were directly pressed/integrated onto a printed circuit board (PCB) using the Cu metallisation as a ground plane for the design and fabrication of a circularly polarized microstrip patch antenna suitable for satellite navigation systems which achieved efficiencies 87% at 1561 MHz (BeiDou) and 88% at 1575 MHz (GPS/Galileo). The low cost, low energy integration of temperature stable, cold sintered ceramics directly onto a PCB represents a step change in substrate fabrication technology for RF devices.

Performance of borosilicate glass/Ba3(VO4)2 ceramic composites and chemical stability with Ag electrodes

In the present work, a systematic study on performance of borosilicate glass/Ba3(VO4)2 ceramic composites synthesized by the traditional solid-state reaction method was conducted. Borosilicate glass is beneficial for reducing the sintering temperature of glass/Ba3(VO4)2 ceramic composites below 900 °C due to the formation of a liquid phase. The ceramic composites with 35 %∼40 % Ba3(VO4)2 can effectively adjust the temperature coefficient of resonant frequency (τf) to approximately 0. The diffusion activation energy (QAg) increases from 113.92 kJ/mol to 185 kJ/mol, as Ba3(VO4)2 content increases from 0 to 40 % in the ceramic composites. A 0.65 borosilicate glass-0.35Ba3(VO4)2 ceramic composite possesses excellent properties including an εr of 8.66, Q × f value of 20,338 GHz, the largest volume resistivity of 5.1 × 1013 Ω·cm and a flexural strength of 259 MPa. Ag exists only in the zero-valence state in the ceramic composite, and Ba3(VO4)2 ceramic can block the diffusion channels and increase the barrier to the movement of Ag ions.

High-performance ZnTiNb2O8 microwave dielectric ceramics produced from ZnNb2O6–TiO2 nano powders

Abstract Ixiolite-structured ZnTiNb2O8 (ZTN) ceramics were prepared by the simple but effective route of reaction sintering ZnNb2O6 and TiO2 nano powders. The effect of sintering temperature and soaking time on the densification behavior, microstructure evolution and microwave dielectric properties of the synthesized ZTN ceramics were systematically studied. Nano ZnNb2O6 and TiO2 raw materials were mixed, pressed and sintered directly into ceramic bodies without any calcination step involved. The sintered samples were characterized by Field-Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), and microwave dielectric measurements. Single-phase ZnTiNb2O8 ceramics with relative densities up to 97% theoretical density were achieved by sintering at 975–1075 °C. The ixiolite ZTN ceramics reaction sintered at 1050 °C for 3 h exhibited excellent microwave dielectric properties with a dielectric constant ( e r ) = 35.5, quality factor (Q × f0) = 52,500 GHz and a temperature coefficient of resonant frequency ( τ f ) = −60 ppm/°C. These results demonstrate that high-performance ZTN microwave dielectric ceramics can be successfully produced by the simple and efficient reaction-sintering method.

High-Q Li2Mg2(MoO4)3 dielectrics for LTCC applications at microwave frequencies

ABSTRACT Li2Mg2(MoO4)3 dielectric was prepared via the conventional solid-state method, and its dielectric properties were investigated in the microwave frequency region. The XRD patterns of the sintered samples revealed single-phase formation with an orthorhombic structure and a space group belonging to Pnma(62). Lattice parameters, bond length, and Raman spectra of the ceramics were also investigated. The dielectric properties exhibited significant dependence on the sintering conditions. The values (resonant frequency temperature coefficient) remained in a range from – 60 to – 69 ppm/°C for all specimens because the changes in the unit cell volume were small. Excellent microwave dielectric properties (εr ~ 9.5, Q × f ~ 80,000 GHz and τf ~ – 69 ppm/°C) can be obtained for Li2Mg2(MoO4)3 ceramics sintered at 880°C for 4 h. This constitutes a very promising material for LTCC applications.

Microwave dielectric properties of Mg4Nb2−x(Zr1/2W1/2)xO9 ceramics

The relationship between the microwave dielectric properties and structural characteristics of Mg4Nb2−x(Zr1/2W1/2)xO9 (0.05 ≤ x ≤ 0.15) ceramics was investigated along with the microwave dielectric properties of Mg4Nb2−x(Al1/3W2/3)xO9 (0.05 ≤ x ≤ 0.15) ceramics for comparison. The quality factors (Qf) of Mg4Nb2−x(Zr1/2W1/2)xO9 (MNZW) and Mg4Nb2−x(Al1/3W2/3)xO9 (MNAW) were proportional to the average bond valence of the Nb-sites. Mg4Nb1.95(Zr1/2W1/2)0.05O9 (Vavg.B= 3.014), which has a higher average bond valence (VB) than that of Mg4Nb2O9 (VB = 2.991), showed an excellent Qf; however, Qf decreased with further substitution. With an increase in the substitution content, the dielectric constant (K) of the specimens decreased, because the dielectric polarizability of the Nb5+(3.97 A3) was larger than that of the substitution ions such as (Zr1/2W1/2)5+ (3.225 A3) and (Al1/3W2/3)5+ (2.397 A3). The temperature coefficients of resonant frequency (TCF) of the specimens decrease as the K value decreases.

The effects of TiO2 addition on microwave dielectric properties of Y3MgAl3SiO12 ceramic for 5G application

In this paper, thermal stable Y3MgAl3SibO12-TiO2 microwave composite ceramics were firstly fabricated by the high temperature solid phase reaction method. The influence of the sintering temperature, microstructure on microwave dielectric properties of Y3MgAl3SiO12 by doping TiO2 were investigated in detailed. TiO2 addition reduced the ceramic sintering temperature and improved the distribution of grain size. The negative temperature coefficient of resonant frequency (τf = −32 ppm/°C) of Y3MgAl3SiO12 was adjusted to near zero value. 0.8Y3MgAl3SiO12-0.2TiO2 ceramic sintered at 1475 °C for 6 h achieved the optimized microwave dielectric properties: εr = 12.2, Q × f = 21,050 GHz, τf = +5.2 ppm/°C, which indicated that 0.8Y3MgAl3SiO12-0.2TiO2 is a potential candidate for dielectric patch antenna and substrate.

Temperature Stable and Low Loss Microwave Dielectric Ceramics of Li2Mg3-xSrxTiO6

In this paper, a series of Li2Mg3-xSrxTiO6 (x = 0, 0.02, 0.04, 0.06, 0.08) ceramics were prepared by the conventional solid-state reaction method. The effects of Sr2+ substitution on the structure, morphology and microwave dielectric properties of Li2Mg3TiO6 ceramics were investigated. The X-ray diffraction (XRD) results indicated that Li2Mg3TiO6 and SrTiO3 phases stably coexisted with each other and formed composite materilas. The appearance of porous structure mainly originated from the volatilization of lithium at high sintering temperatures. As the Sr2+ content increased from 0 to 0.08, the optimum dielectric constant (ε r ) increased from 13.61 to 17.32, the quality factor (Q×f) decreased monotonously and the temperature coefficient of resonant frequency (τ f ) changed from -34.4 to +16.8 ppm/°C. The variations of ε r , Q×f and τ f could be explained by the Lichtenecker logarithmic model and mixing rule, respectively. In particular, optimal microwave dielectric properties of ε r = 16.08, Q×f = 82100 GHz, τ f = +1.7 ppm/°C were obtained for Li2Mg2.94Sr0.06TiO6 ceramic sintered at 1310 °C for 5h.

Synthesis, lattice energy and microwave dielectric properties of BaCu2-xCoxSi2O7 ceramics

BaCu2-xCoxSi2O7 solid solutions with orthorhombic structure (Pnma) were prepared by solid-state reaction method. The phase synthesis process, structural evolution and microwave dielectric properties of BaCu2-xCoxSi2O7 ceramics were investigated. Single BaCu2Si2O7 phase was obtained when calcined at 950 °C for 3 h and was decomposed into BaCuSi2O6 phase when calcined at 1075 °C for 3 h. The sintering process was effectively promoted when Cu2+ was replaced by Co2+ and the maximum solubility of BaCu2-xCoxSi2O7 was located between 0.15 and 0.20. P-V-L complex chemical bond theory and Raman spectra were used to explain the structure-property correlations of BaCu2-xCoxSi2O7 ceramics. The corrected dielectric constant (εr-corr) of BaCu2-xCoxSi2O7 ceramics decreased monotonously with the susceptibility (Σχμ) and ionic polarizability of primitive unit cell. The quality factor (Q × f) increased with bond strength and lattice energy (Ucal), especially the lattice energy of the Si-O bond. The temperature coefficient of resonant frequency (τf) was determined by the susceptibility and lattice energy of the Cu/Co-O bond. The following optimum microwave dielectric properties were obtained at x = 0.15 when sintered at 1000 °C for 3 h: εr = 8.45, Q×f =58958 GHz and τf = -34.4 ppm/°C.

High relative permittivity Bi4B2+xO9+3x/2 (x = 1.5, 2, 2.5, 3) microwave ceramics for ULTCC technology

Bi4B2+xO9+3x/2 (x = 1.5, 2, 2.5, 3) compounds with high relative permittivity and ultra-low sintering temperature were prepared using the conventional solid-state method. Due to the volatilisation of B2O3 during sintering, a Bi4B2O9 single phase was obtained in excess addition of boric acid for x = 2.5. The densest structure of the Bi4B2+xO9+3x/2 (x = 2.5) ceramic, sintered at 585 °C, exhibited good microwave dielectric properties of a relative permittivity (εr) = 42.5, quality factor (Q × f) = 3240 GHz, and temperature coefficient of resonance frequency (τƒ) = −59 ppm/°C. As the value of x changed, the second phases of Bi2O3 and Bi3B5O12 appeared, and the (εr) and (τƒ) values decreased. The Bi4B2+xO9+3x/2 (x = 2.5) ceramics did not react with either Ag or Al, indicating that they are good candidate materials for ultra-low temperature co-fired ceramic (ULTCC) applications.

Dielectric Properties of a New Ceramic System (1-x)(Mg<sub>0.95</sub>Zn<sub>0.05</sub>)<sub>2</sub>TiO<sub>4</sub>-x(Ca<sub>0.8</sub>Sr<sub>0.2</sub>)TiO<sub>3</sub> at Microwave Frequencies

The microwave dielectric properties and microstructures of the (1-x)(Mg0.95Zn0.05)2TiO4-x (Ca0.8Sr0.2)TiO3 ceramics prepared using the conventional solid-state route were investigated. The structure and microstructure were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Ilmenite-structured (Mg0.95Zn0.05)TiO3 was detected as a second phase. The coexistence of the second phase, however, did not degrade the dielectric properties of the specimen because the phases were compatible. At x = 0.07, a dielectric constant (εr) of ~17.86, a quality factor (Q×f) value of ~ Q×f~133,600 Hz (at 10 GHz), and a temperature coefficient of resonant frequency (τf) of ~ –5ppm/°Cwere obtained for 0.93(Mg0.95Zn0.05)2TiO4-0.07(Ca0.8Sr0.2)TiO3 ceramic sintered at 1240°C for 4 hr. The dielectric is proposed as a candidate material for low-loss microwave and millimeter wave applications.

Structure and microwave dielectric properties of BaAl2−2x(CuSi)xSi2O8 ceramics

The sintering behavior, phase composition, microstructure and dielectric properties of BaAl2−2x(CuSi)xSi2O8 (x = 0, 0.01, 0.015, 0.02, 0.04, 0.06, 0.08) ceramics prepared via solid-state reaction route were investigated. Deviation between theoretical and experimental permittivity of BaAl2Si2O8 ceramics was discussed, and the theoretical and experimental temperature coefficient of resonant frequency (τf) was also compared. The results showed that substituting (Cu0.5Si0.5)3+ for Al3+ in matrix of hexacelsian could lower the sintering temperature from 1400 to 1200 °C and greatly promote the transformation of hexacelsian-to-celsian. And the single celsian phase was obtained for the compositions with x ≥ 0.02. The bulk densities, microstructure and dielectric properties of BaAl2−2x(CuSi)xSi2O8 ceramics were improved by doping a small quantity of (Cu0.5Si0.5)3+ ions in the BaAl2Si2O8. The BaAl1.96(CuSi)0.02Si2O8 ceramics sintered at 1300 °C obtained good microwave dielectric properties: er = 6.7, Q × f = 31,276 GHz, τf = − 17.17 × 10−6 °C−1.

Crystal structure, phonon modes, and bond characteristics of AgPb2B2V3O12 (B = Mg, Zn) microwave ceramics

AbstractAgPb2B2V3O12 (B = Mg, Zn) ceramics with low sintering temperature were synthesized via the conventional solid‐state reaction route. Rietveld refinements of the X‐ray diffraction patterns confirm cubic symmetry with space group . The number of observed vibrational modes and those predicted by group theoretical calculations also confirm the space group. At the optimum sintering temperature of 750°C/4 hours, AgPb2Mg2V3O12 has a relative permittivity of 23.3 ± 0.2, unloaded quality factor () of 26 900 ± 500 GHz (), and temperature coefficient of resonant frequency of 19.3 ± 1 ppm/°C, while AgPb2Zn2V3O12 has the corresponding values of 26.4 ± 0.2, 28 400 ± 500 GHz () and –18.4 ± 1 ppm/°C at 590°C/4 hours. Microwave dielectric properties of a few reported garnets and Pb2AgB2V3O12 (B = Mg, Zn) ceramics were correlated with their intrinsic characteristics such as the Raman shifts as well as width of A1g Raman bands. Higher quality factor was obtained for lower full width at half‐maxima (FWHMs) values of A1g modes. The increase in B‐site bond valence contributes to high and low |τf| with the substitution of Zn2+ by Mg2+. Furthermore, the high ionic polarizability and unit cell volume with Zn2+substitution contribute to increased relative permittivity.