Microwave Dielectric Properties Research Articles

Microwave dielectric properties of Na2O–Ln2O3–MoO3–TiO2 (Ln = Nd, La and Ce) system with low‐sintering temperature

AbstractThis study examines the low‐loss and temperature‐stable Na2O–Ln2O3–MoO3–TiO2 (Ln = Nd, La and Ce) system, synthesized via a solid‐state process at low‐sintering temperatures ranging from 840°C to 900°C The structure, microstructure and microwave properties of the Na0.5Ln0.5MoO4–TiO2 (Ln = Nd, La and Ce) ceramics as a function of the sintering temperature were studied. The results of XRD patterns and microstructure characterization showed that the main phase in compositions belong to tetragonal scheelite and tetragonal structure. The ceramic composition Na0.5Ln0.5MoO4–TiO2 (Ln = Nd, La and Ce), sintered at 840°C–900°C for 2 hours, demonstrated excellent microwave dielectric properties, exhibiting relative dielectric constant (εr) of 13.9–14.4, Q × f value of about 31 100 (at 9.66 GHz) – 48 600 GHz (at 9.33 GHz), and temperature coefficient of –8.1 to –1 ppm/°C. Our work designs temperature‐stable microwave dielectric ceramics with low‐sintering temperature for LTCC technology applications.

Correlation between chemical bond characteristics and microwave dielectric properties of KLa(MoO4)2 ceramics

This investigation details the synthesis process of KLa(MoO4)2 ceramic utilizing a solid-state route method, alongside an analysis of its structural characteristics and the correlation between chemical bonds and microwave dielectric properties. The KLa(MoO4)2 phase was identified to possess a Monoclinic structure (C2/c space group). Sintering the sample at 820 °C resulted in a maximum relative density of 94.6% and impressive microwave characteristics: εr = 9.63, Q×f = 50,100 GHz, and τf = -75.7 ppm/°C. Correlations between relative density and dielectric properties were observed. Further, application of the P-V-L bond theory facilitated the analysis of chemical bond parameters and their impact on microwave dielectric properties. The dielectric properties were correlated to chemical bond iconicity, packing fraction, lattice energy and bond valences.

Effects of phase transition on the structure and microwave dielectric properties of (1-x)CeO2-0.5xSm2O3 (x=0-0.9) ceramics

(1-x)CeO2-0.5xSm2O3 (x=0-0.9) microwave dielectric ceramics are synthesized by the conventional solid-phase reaction method, with the effects of phase transition on structure and microwave dielectric properties being investigated in detail. The phase transition process is analyzed using the ionicity and lattice energy of (1-x)CeO2-0.5xSm2O3 ceramics, which is related to the coordination number and effective valence electron charge. With the increase of Sm3+ content, there are three phase regions: the cubic fluorite phase (0 ≤ x ≤ 0.4), the rare-earth C-type phase (0.4 <x ≤ 0.8) and the mixed phase (0.8 <x < 1.0). With the phase transition, the microstructures of (1-x)CeO2-0.5xSm2O3 (x=0-0.9) ceramics show a quasi-periodic change, where x=0.4 and x=0.8 are the critical points with similar grain size and distribution. When the phase transition occurs, the polarization, Q׃ values and the resonant frequency temperature coefficients (τƒ) of (1-x)CeO2-0.5xSm2O3 (x=0-0.8) ceramics are all mutated, which is due to the change of bond ionicity and effective valence electron charge caused by the phase transition. The microwave dielectric properties in each pure phase region vary regularly with bond ionicity and valence. Compared with the cubic fluorite phase (0 ≤ x ≤ 0.4), (1-x)CeO2-0.5xSm2O3 ceramics with rare-earth C-type phase (0.4 <x ≤ 0.8) have lower dielectric constant, with better Q׃ values and τƒ values.

Synthesis and characterization of La2O3-Al2O3-SiO2 glass ceramics for electronic substrate application

Fracture-resistant glass ceramic materials are critical for the advancement of electronic substrates. In this study, we successfully synthesized La2O3-Al2O3-SiO2 glass ceramics through the solid-state method. Comprehensive investigations were conducted into their phase composition, crystallization kinetics, microstructure, mechanical, thermal expansion, and microwave dielectric properties. The Kissinger, Ozawa, and Augis-Bennett methods are all appropriate for characterizing glass crystallization behavior. Mechanical testing results showed a sample with a composition of 45wt% La2O3-30wt% Al2O3-25wt% SiO2 exhibited superior properties attributed to its high crystallinity and dense microstructure, including the highest flexural strength (229.4MPa), Vickers hardness (8.78GPa), elastic modulus (118.7GPa), and fracture toughness (2.8MPa·m1/2). Notably, the fracture toughness values obtained using the VIF and SENB methods were significantly higher than those obtained using the EM method, and the validity of the data was confirmed by Weibull distribution analysis. These findings underscore the potential application of the developed glass ceramics in the field of electronic substrates.

Crystal structure, chemical bonds, and microwave dielectric properties of NaZnPO4 ceramic

Crystal structure, chemical bonds, and microwave dielectric properties of NaZnPO4 ceramic

Effect of binary ion substitution on the crystal structure and microwave dielectric properties of MgTa2O6 ceramics

AbstractMg1/3A11/3A21/3Ta2O6 ceramics (where A1 and A2 represent Co, Ni, or Zn) were prepared using the solid‐phase reaction route. The results of X‐ray diffraction and Raman tests showed that (Co1/2Ni1/2)2+, (Co1/ 2Zn1/2)2+, and (Ni1/2Zn1/2)2+ ions replaced Mg2+ ions in the lattice of MgTa2O6, resulting in the formation of a pure tri‐rutile structure. All three complex ions could significantly reduce the sintering temperature of the ceramics (by 150°C–200°C) and could broaden the sintering window. The large deviation (48.8%–69.2%) between the porosity corrected relative permittivity εr‐corr. and the theoretical relative permittivity εr‐theo. might be due to the overestimation of the ionic polarizability of Ta5+ by Shannon. (Co1/2Ni1/2)2+ has the most significant effect of increasing the bond energy of ceramic A–O bonds, reducing the τf value from 51 to 36 ppm/°C. In addition, the mechanisms affecting their dielectric properties are discussed based on bond ionicity (fi), full width at half maximum (FWHM) of Raman peak, and bond energy (E). Mg1/3Co1/3Ni1/3Ta2O6 ceramic sintered at 1350°C have the most excellent microwave dielectric properties: εr = 26.8, Q × f = 86,000 GHz, and τf = 36 ppm/°C.

Ta doping effect on microstructure and microwave dielectric properties of CoNb2O6‐based ceramics and mechanism study

AbstractAs communication technology continues to evolve, 5G technology is becoming more mature, and 6G technology is steadily advancing. Microwave equipment is moving toward high frequency, miniaturization, low loss and high temperature stability, and microwave dielectric ceramics have been deeply applied in this field. To elevate the Q × f value of CoNb2O6 system, Ta5+ was introduced into CoNb2O6, and CoNb2‐xTaxO6 (0.0 ≤ x ≤ 0.8) ceramics were prepared by the traditional solid‐phase method. By X‐ray diffraction, it was observed that at x = 0.8, in addition to a single niobium ferrite phase, information of tantalate phase also appeared. Raman spectral detection and group theory analysis indicate that Ag(2) and Ag(3) modes are the dominant Raman vibrations at ≈873 cm−1. Furthermore, the polarization rate affects the εr value, and the bond energy of Nb/Ta‐O and the recovery force characterized by the average deformation of the [Nb/TaO6] octahedron are the key elements influencing the temperature coefficient of the resonance frequency (τf). The internal strain, ordered induced size, and chemical bonding valence of ionic valence states are the key factors that can increase the Q × f value. Moreover, the introduction of ions with lower electronegativity leads to an enhanced electronic compensation of oxygen vacancies, which also reduces the dielectric loss. This paper enriches the theory related to low dielectric loss and shows that CoNb1.8Ta0.2O6 (εr = 21.4832, Q × f = 100723 GHz, τf = ‐61.38 ppm/°C) ceramics with superior microwave dielectric properties are expected to be used in wireless communication devices.

Significantly reduced lattice defects and improved dielectric properties of MgTiO3 based microwave ceramics via supercritical-fluid assisted oxidation technology

Lattice defects play a crucial role in determining the microwave dielectric properties of ceramics. We herein report a simple way to significantly improve the dielectric properties of MgTiO3 based microwave ceramics by restoring the oxygen vacancy via supercritical assisted oxidation (SAO) technology. The high penetrability of SCCO2 fluid makes the OH− groups easy to approach oxygen vacancy, which react with the dangling bonds to form A-O-A (A=Ti/Mg) covalent coordinate bonds. The oxygen vacancy concentration in MgTiO3-CaTiO3 ceramics significantly decreases from 26.7 % to 18.5 % and the Ti-O bond strength is strengthened after SAO treatment. Furthermore, the activation energy Ea increases to 0.60 eV from 0.52 eV, indicating a lower defects density as well. Consequently, MgTiO3-CaTiO3 ceramics treated by SAO exhibit better high-temperature stability in dielectric properties and the Q×f values of MgTiO3-CaTiO3 ceramics increase by 11.3∼19.0 % due to the decreased defects concentration, thereby demonstrating the potential of supercritical fluid technology in achieving performance optimization of microwave dielectric ceramics.

Design and Fabrication of a C-Band Patch Antenna with Low Loss BaM4Si5O17 Microwave Dielectric Ceramics.

Single-phase BaM4Si5O17 (M = Yb, Er, Y, Ho) ceramics have been investigated for their crystal structures, microwave dielectric properties, flexural strength, and potential applications in dielectric antennas. Rietveld refinement and TEM analysis revealed that the BaM4Si5O17 ceramics exhibit a monoclinic structure (space groups: P21/m). The εr of the BaM4Si5O17 ceramics was dominated by ionic polarizability and ρrel. The Q × f values were considerably larger at BaM4Si5O17 (M = Yb and Y) ceramics with the high Utotal and low intrinsic dielectric loss. The τf values were controlled by the MO6 octahedron distortion and -VBa. The flexural strength was mainly dominated by pores and average grain size and reached the maximum value (156 MPa) at BaY4Si5O17 ceramic with small average gain sizes and high relative density. Additionally, a patch antenna was fabricated using high-performance BaY4Si5O17 ceramic characterized by a εr value of 9.02, a Q × f value of 60620 at 12.30 GHz, and a τf value of -37.65 ppm/°C. This design achieved a high simulated radiation efficiency of 82.70% and a gain of 5.60 dBi at 6.97 GHz. indicating potential applications of BaY4Si5O17 ceramic because of its low dielectric loss and high flexural strength.

Structural characteristics, P-V-L theory, Raman spectra, and microwave dielectric properties of (La1-xNdx)2(Zr0.96Ti0.04)3(MoO4)9 ceramics for LTCC applications

This article explores the microwave dielectric properties of (La1-xNdx)2(Zr0.96Ti0.04)3(MoO4)9 (x=0.1,0.3,0.5, and 0.7) ceramics prepared by solid-state reaction. Utilizing the Rietveld refinement technique in XRD, the sample is identified as a trigonal crystal system belonging to the R3¯c space group. SEM analysis indicates that relative density has a significant impact on the εr and Q×f of ceramics. The Q×f values of ceramics are closely related to the FWHM of the Raman spectra. At 750℃, (La0.5Nd0.5)2(Zr0.96Ti0.04)3(MoO4)9 ceramic exhibited excellent dielectric properties: εr = 10.4 (±0.08), Q×f = 149,300 (±3211) GHz, τf = −34.8 (±0.7) ppm/℃. To gain a deeper understanding of the intrinsic mechanisms governing the microwave dielectric properties of ceramics, analysis based on the P-V-L theory reveals that the La(Nd)-O bond and Mo-O bond contribute significantly to εr and Q×f, respectively.

Resolving the Role of Configurational Entropy in the Optimization of Mechanical, Thermal, and Microwave Dielectric Properties of SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 Ceramics.

The demand for high-performance microwave dielectric ceramics has surged with the proliferation of fifth-generation (5G) communication networks. In this work, SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 (x = 0-0.20) ceramics were designed by leveraging the unique properties of SrLaAlO4 ceramics and high-entropy engineering. The effects of configurational entropy (Sconf = 1.23R - 1.54R) on the mechanical, thermal, and microwave dielectric properties of SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 ceramics were investigated. X-ray diffractometer and transmission electron microscope analyses confirmed that each composition belonged to the tetragonal structure with a space group of I4/mmm. Significant improvements in Vickers hardness were observed with increasing Sconf, reaching 8.05 GPa at Sconf = 1.54R compared to 5.64 GPa in SrLaAlO4 ceramics. Additionally, the increasing entropy showed great potential in reducing the thermal expansion coefficient (CTE) from 12.32 to 11.49 ppm/°C. The optimal quality factor (Q × f) of 98,000 GHz was achieved at Sconf = 1.37R, attributed to the optimization of intrinsic lattice energy and infrared-damped modes. The temperature coefficient of resonant frequency (τf) was successfully modified toward zero due to entropy-driven CTE and structural modifications. Excellent microwave dielectric properties with εr = 22.5, Q × f = 98,000 GHz, and τf = -2.0 ppm/°C were obtained at Sconf = 1.37R. This work highlights the potential of entropy-engineering in developing high-performance microwave dielectric ceramics, offering a promising pathway for the advancement of 5G communication components.

Crystal structure, microwave dielectric properties, and far-infrared spectroscopy of a novel low-dielectric constant tremolite ceramic CaZnGe2O6

The diopside-structured CaZnGe2O6 ceramics were synthesized using the conventional solid-state reaction method in this study, and their crystal structure, microstructural evolution, and microwave dielectric properties were systematically investigated. The XRD and Rietveld refinement analyses confirmed that CaZnGe2O6 crystallizes in the monoclinic crystal system with a C2/c space group. The intrinsic microwave dielectric properties of the ceramics were evaluated using far-infrared spectroscopy. The ceramic structure exhibits high density and microstructural homogeneity after sintering at 1130 °C, resulting in exceptional microwave dielectric properties achieved at this optimal temperature (εr = 8.78 Q×f = 63,782 GHz, τf = −66.4 ppm/°C). These findings highlight the potential application of CaZnGe2O6 ceramics as low-permittivity materials suitable for microwave devices.

Substitution of Ce4+ for ionic at both A/B sites greatly improves the microwave responses of (Sr0.9Ca0.1)1/2La1/2Al1/2Ti1/2O3 perovskite ceramics

In this paper, (Sr0.9Ca0.1)1/2La1/2Al1/2Ti1/2O3-x wt.% CeO2 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics were synthesized via solid state reaction. The effects of Ce4+ doping on microstructure and microwave dielectric properties were studied. All samples crystallized as perovskite single-phase. Ce4+ substitution for La3+ occurred at the A site for 0 < x ≤ 0.4, and for Ti4+ at the B site for 0.4 ≤ x ≤ 0.5. Oxygen vacancy concentration was linked to substitution sites, decreasing for x ≤ 0.3 and increasing for x ≥ 0.4, as shown by XPS analysis. The quality factor was influenced by oxygen vacancies, grain size, and packing fraction. Bonding valence and oxygen octahedral distortion affected the temperature coefficient of resonant frequency. At x = 0.4 and sintered at 1570 °C, the ceramics showed excellent properties: εr = 38.83, Q×f = 54058 GHz, τf = 2.137 ppm/°C, making it a promising low-loss dielectric ceramic for microwave communication applications.

Enhancing structural strength and microwave dielectric properties of the Ba4(Sm1-xCex)9.33Ti18O54 ceramics

Herein, microwave dielectric ceramics of the Ba4Sm9.33Ti18O54 ceramics are substituted at A sites by partially replacing Sm at A1 sites with Ce, and the effects of ionic substitution at A sites on ceramic crystal structure and microwave dielectric properties are investigated. The Ba4(Sm1-xCex)9.33Ti18O54 (BSCT) ceramics prepared through the solid phase method has a typical tungsten–bronze structure, and its lattice spacing increases gradually with the increase in Ce content x. This increase is reflected in the increase in the cell volume and growth of ceramic grains. However, the excess Ce after Ce content exceeds 0.25 leads to the growth of ceramic grains and increase in porosity between grains, which in turn increases the dielectric loss of the ceramic. Under optimal sintering conditions, the ceramic crystal has a maximum atomic packing density of x = 0.25, which corresponds to its most stable structural properties, and the highest Q × f value of 9013 GHz. Raman spectroscopy results indicate that in titanium oxygen octahedrons, an increase in Ce substitution can effectively weaken the bending and tensile vibration intensities of titanium oxygen bonds, further enhancing structural strength.

A Novel Microwave Dielectric Ceramic LiSrVO4 for LTCC

Abstract LiSrVO4 (LSV) ceramics were prepared using the solid-state synthesis method, and their phase structure, morphology, sintering characteristics, and microwave dielectric properties were investigated. The LSV ceramics could be densified by sintering at 875–925 °C for 4 hours. XRD indicated that LSV ceramics sintered at 875–925 °C for 4 hours were singlephase ceramics with a monoclinic structure. With the increase in sintering temperature, the dielectric constant and quality factor of LSV ceramics first increased and then decreased, while the temperature coefficient of the resonant frequency gradually decreased. LSV ceramics sintered at 900 °C for 4 hours exhibited a εr of 10.92, a Q×f value of 21115 GHz, and a τf of -4 ppm/°C. LSV ceramics demonstrated good chemical compatibility with silver, showing promising potential in the field of Low-Temperature Co-fired Ceramics.

Microwave dielectric properties and phase evolution of Zn-excess Mg0.95Zn0.05+xTiO3+x (x = 0–0.1) ceramics

Microwave dielectric properties and phase evolution of Zn-excess Mg0.95Zn0.05+xTiO3+x (x = 0–0.1) ceramics

Low-temperature sintered Li2BaP2O7 ceramic: structural insights, bond characteristics, and microwave dielectric properties

The Li2BaP2O7 ceramics, synthesized through the solid-state reaction method, exhibit a pure monoclinic phase. Upon sintering at 750 °C, the ceramic achieves a high relative density of 97.3%, which is indicative of an optimal microstructure conducive to the superior microwave dielectric properties: a εr of 9.9, a Q × f of 86200 GHz, and a τf of -95.4 ppm/°C. The variation in relative density is identified as the principal driver of changes in both the εr and Q × f values for the Li2BaP2O7 ceramics. The molecular polarizability is pivotal in determining the εr of Li2BaP2O7 ceramics. The P-V-L theory analysis elucidates that the P-O bond significantly surpasses other chemical bonds in contributing to the ionicity, lattice energy, and bond energy, thereby underscoring its dominance over the three principal microwave dielectric characteristics. Furthermore, Raman spectroscopy data demonstrate that the P-O bond vibration predominantly governs the overall vibrational spectrum.

A novel LiMg2P3O10 microwave dielectric ceramic for ultra-wideband dielectric resonant antenna applications

In pursuit of the objective of implementing fifth-generation communication technology, a LiMg2P3O10 microwave dielectric ceramic was developed in this study, and an ultra-wideband dielectric resonant antenna was fabricated. Rietveld refinement confirmed that the monoclinic crystal structure of LiMg2P3O10 ceramics is constituted of MgO6 octahedral chains and shared angle PO4 tetrahedra. The impact of chemical bond characteristics on properties was explored through P-V-L theory. The primary contributions to the intrinsic properties were investigated through infrared spectroscopy. The LiMg2P3O10 ceramics sintered at 830 °C were found to have the best microwave dielectric properties (εr = 6.16, Q × f = 33,573 GHz (at 15.538 GHz), and τf = −35.6 ppm/°C). A novel ultra-wideband dielectric resonant antenna with 53.7 % relative bandwidth, 6.53 dBi maximum gain and 81.7 % radiation efficiency was designed and fabricated. Its wide ultra-wideband characteristics makes it suitable for signal transmission in modern wireless communication systems.

Microwave dielectric properties of LiM(PO3)3 (M = Mg2+, Zn2+) ceramics

Microwave dielectric ceramics with low dielectric permittivity εr combined with low ceramic sintering temperatures have raised considerable research interest recently due to their potential application in LTCC technology for 5G wireless communications. Here in this study, ceramic processing, crystal structure, and microwave dielectric properties of LiM(PO3)3 (M = Mg2+, Zn2+) ceramics were comprehensively investigated. Optimized LTCC compatible ceramic sintering processes were developed at 725 °C and 625 °C for 10 hours, respectively, leading to high relative densities of 96.27% and 94.09%. Low microwave εr values of 5.74 and 6.30 and Q×f values of 16,660 GHz and 9,629 GHz (at 14 GHz) were obtained, where such values were found to be affected by the grain microstructure. LiMg(PO3)3 exhibited a small τf of -11 ppm/°C, while LiZn(PO3)3 showed -58 ppm/°C. Complementary impedance spectroscopy measurements indicated modest Li+-ion conductivity with a higher value of 2.92·10-7 (Ωcm)-1 at 560 K (287 °C) in LiZn(PO3)3. Both ceramics were found to be dielectrically homogeneous without any perceptible contributions from the grain boundaries.

Sintering behavior, lattice vibrational characteristics and dielectric properties of B-site ion substituted BaWO4 ceramics for LTCC applications

The influences of Mo6+ substitution at the B-site of scheelite structure on the sintering character, microstructures, lattice vibrational characteristics, and dielectric properties of BaW1-xMoxO4 (x = 0.10-0.30) ceramics were studied in detail in this paper. The sintering temperature of BaW1-xMoxO4 ceramics was effectively reduced to less than 950oC through forming a scheelite solid solution. The densification and the quality factor (Q×f) of BaW1-xMoxO4 ceramics were also enhanced compared with pure BaWO4 ceramic. Raman spectroscopy confirmed that the dielectric constant (εr) was highly correlated with molecular polarizability, and the Q×f was strongly dependent on the symmetric stretching bond of [WO4] tetrahedron. Oxygen bond valence was one of crucial parameters for modulating the temperature coefficient of resonant frequency (τf). Interestingly, the BaW0.75Mo0.25O4 ceramic sintered at 910oC exhibited favorable microwave dielectric properties of εr = 9.44, Q×f = 46,820GHz (@12.5GHz), and τf = −69.2 ppm/oC. Meanwhile, the BaW0.75Mo0.25O4 ceramic had stupendous dielectric properties in low-frequency band: εr = 17.5 and dielectric loss (tanδ) = 2.2×10-4 (@10MHz). In addition, there was good chemical compatibility between BaW0.75Mo0.25O4 ceramic and silver electrodes. These findings evidence that BaW1-xMoxO4 ceramics are competitive candidates in LTCC technology.