Microwave Dielectric Ceramics Research Articles

Enhanced dielectric properties and chemical bond characteristics of ZnNb2O6 ceramics due to zinc oxide doping

Regarding advanced 5G mobile communication, microwave dielectric ceramics are considered as the most potential materials to develop new-generation base station resonators. Herein, ZnNb 2 O 6 ceramics with ε r of approximately 24 have been prepared using the solid-state reaction method, with tailored extra ZnO of x mol% (x = 1, 2 and 3). We have for the first time applied the P-V-L chemical bond theory to investigate ZnNb 2 O 6 ceramics with ZnO doping, by exploring the relationship of dielectric properties and chemical bond characteristics. Particularly, the Raman spectra demonstrates that the full width at half maximum of υ 1 (A g ) vibration mode can exhibit significant correlation with the quality factor ( Q × f ). To further support the experimental study, we have also conducted the first-principle calculation of electron density difference via CASTEP package, which further confirms the change of temperature coefficient of resonance frequency ( τ f ). Our newly designed ZnNb 2 O 6 ceramics doped with 1 mol% ZnO exhibit excellent dielectric properties, i.e., ε r = 23.74, Q × f = 102,824 GHz and τ f = −55.38 ppm/°C, which demonstrates great potential to construct miniaturized 5G base station with advanced ceramic dielectrics.

Ultra-low dielectric loss lithium-based, temperature stable microwave dielectric ceramics

The low loss and small density of lithium-based microwave dielectric ceramics (MWDCs) make them promising for communication devices such as dielectric filters, antennas, and substrates. In this study, (1- x )[Li 2 Ti 0.98 Mg 0.02 O 2.96 F 0.04 −1 wt%Nb 2 O 5 ]- x Li 3 Mg 2 NbO 6 (LTMN 0.02 -LMN, 0 ≤ x ≤ 0.1) MWDCs fabricated via solid solution reaction were successfully synthesized to obtain a near-zero temperature coefficient of the resonant frequency (τ f ). The X-ray diffraction pattern and Rietveld refinement results showed that a good solid solution was formed and that the phase composition of the LTMN 0.02 system gradually changed from monoclinic to cubic. Scanning electron microscopy images revealed that the microstructure of LTMN 0.02 improved as the LMN content increased. Ultimately, desirable dielectric properties were obtained by sintering at 1220 °C with x = 0.08: ε r ∼18.1, Q × f ∼105,661 GHz, and τ f ∼ + 1.3 ppm/°C. Furthermore, the highest Q × f value (∼131,157 GHz) was achieved in the x = 0.04 composition with relatively homogeneous grains. The high-performance LTMN 0.02 -LMN ceramics developed in this study provide a new alternative material for the dielectric components of communication systems.

Low-temperature firing and microwave dielectric properties of MgNb2-xVx/2O6-1.25x ceramics

MgNb2-xVx/2O6-1.25x (0.1≤x≤0.6) ceramics with orthorhombic columbite structures were prepared at low-temperature by a solid-phase process. The phase component, microscopic morphology, low-temperature sintering mechanism and microwave dielectric performance of MgNb2-xVx/2O6-1.25x ceramics were comprehensively investigated. Low-temperature sintering densification of dielectric ceramics was achieved via the nonstoichiometric substitution of vanadium (V) at the Nb-site. In contrast to pure MgNb2O6 ceramics, the sintering temperature of MgNb2-xVx/2O6-1.25x (x = 0.2) ceramics was reduced by nearly 300 °C owing to the liquid-phase assisted sintering mechanism. The liquid phase arises from the autogenous low-melting-point phase. Meanwhile, MgNb2-xVx/2O6-1.25x (x = 0.2) samples with nonstoichiometric substitution could achieve a more than 900% improvement in the Q × f value, compared with stoichiometrically MgNb2-xVxO6 (x = 0.1, 0.2) ceramics. Finally, MgNb2-xVx/2O6-1.25x dielectric ceramics possess outstanding microwave dielectric properties: εr = 20.5, Q × f = 91000, and τf = -65 ppm/°C when sintered at 1030 °C for x = 0.2, which provides an alternative material for LTCC technology and an effective approach for low-temperature sintering of Nb-based microwave dielectric ceramics.

Synthesis of low temperature firing scheelite-type BaWO4 microwave dielectric ceramics with high performances

The synthesis of scheelite-structured BaWO 4 ceramics at low temperatures using a Li 2 O–B 2 O 3 –BaCO 3 –CuO (LBBC) glass frit is reported in this study. Composite ceramics with the chemical formula BaWO 4 - x LBBC ( x = 0.25, 0.5, 1, and 2 wt%) were synthesized via the standard solid-phase method. A compact BaWO 4 matrix containing glass crystallized when sintered at 850 °C for only 30 min. The BaWO 4 ceramic with 1 wt% LBBC glass exhibits optimum microwave dielectric performance with Q × f = 58,855 GHz, ε r = 8.33, and τ f = −61.43 ppm/°C. A results of XRD and SEM analyses, microwave properties and the liquid-phase sintering mechanism for the ceramics are presented. • The Q × f value remained excellent for 58855 GHz while the temperature decreased from 1100 °C to 850 °C. • The compound was still the pure BaWO 4 phase. • The shorter soaking time (30min) can effectively reduce the energy consumption.

Ultra-low temperature co-fired ceramics with adjustable microwave dielectric properties in the Na2O–Bi2O3–MoO3 ternary system: a comprehensive study

Na2O–Bi2O3–MoO3 ternary microwave dielectric ceramics with high-performance properties have good potential in the application of LTCC/ULTCC technology.

A new type of microwave dielectric ceramic based on K2O–SrO–P2O5 composition with high quality factor and low sintering temperature

A new type of microwave dielectric ceramics with low dielectric loss was fabricated through a traditional solid-phase method. X-ray diffraction and density tests showed that KSrPO 4 ceramics with a single orthorhombic phase could be synthesized and densified at 950 °C, and the crystal structure of KSrPO 4 was further confirmed by Rietveld refinement analysis. The densification temperature of KSrPO 4 was lower than 961 °C, indicating the ceramics could be used in LTCC devices. Additionally, based on the complex chemical bond theory, some internal parameters of KSrPO 4 ceramics were calculated and the effects of these parameters on the properties of KSrPO 4 were systematically analyzed for the first time. Furthermore, the composite dielectric constant and loss of KSrPO 4 ceramics were analyzed by infrared reflectance spectroscopy, and the theoretical loss and the actual loss were compared. Finally, a vector network analyzer was employed to measure the microwave dielectric properties of all samples. The results showed that KSrPO 4 sintered at 950 °C obtain the best microwave dielectric properties, including ε r = 7.85, Q·f = 34,527 GHz (at 10.43 GHz) and τ f = −14.82 ppm/°C.

Novel series of high-Q oxyfluoride microwave dielectric ceramics for LTCC applications

Three pure phases Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 oxyfluorides were successfully prepared using the way of solid-state reaction method at 650 °C, 600 °C and 725 °C, respectively. According to the XRD data and Rietveld refinement results, these three types of ceramics crystallized in a cubic rock salt structure with space group [Fm-3 m(225)]. The grain sizes, theoretical εtheo and packing fraction were calculated to help with the evaluation of these three ceramics. The oxyfluoride ceramics Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 sintered at 875 °C, 900 °C and 900 °C exhibited outstanding microwave dielectric properties: εr = 16.8, 16.4 and 17.3, Q × f = 76,200, 97,300 GHz and 92,600, and τf = −48.6, − 40.5 and − 41.3 ppm/°C, respectively. The compatibility with Ag powders shows that the Li4NbO4F, Li4MgNbO5F and Li6.5MgTiNbO8F1.5 ceramics are potential candidates for low temperature co-fired ceramic technology.

Phase composition and microwave dielectric properties of Ca0.128Ba0.032Sm0.46Li0.3TiO3 ceramics with alumina addition

Ca0.128Ba0.032Sm0.46Li0.3TiO3-x wt.% Al2O3 microwave dielectric ceramics with temperature stability were prepared by the traditional solid-state reaction method. The effects of Al2O3 doping on phase composition, micromorphology, and microwave dielectric properties of Ca0.128Ba0.032Sm0.46Li0.3TiO3 ceramics were investigated. X-ray diffraction results showed that no other phase was introduced by doping, and the diffraction peaks of all the ceramics could be indexed by standard JCPDS cards of No.42−0423 (CaTiO3) and No.43−0235 (BaSm2Ti4O12). To further study the effects of Al2O3 doping on microstructure and lattice vibration of Ca0.128Ba0.032Sm0.46Li0.3TiO3 ceramics, the structural refinement and Raman spectroscopy techniques were also adopted. Doping Al2O3 decreased the lattice constant of CaTiO3-phase solid solution, modified the morphology and improved microwave dielectric properties of the ceramics. When sintered at 1300 °C for 4 h, the ceramics with 0.9 wt.% Al2O3 showed excellent microwave dielectric properties: εr = 87.9 ± 0.4, Q × f = 6671 ± 103 GHz, and τf = -1.2 ± 0.9 ppm/℃.

Investigation of the microwave dielectric properties of the Li4x/3Zn2−2xTi1+2x/3O4 system by P–V–L theory and vibration spectroscopy

Li 4x/3 Zn 2–2x Ti 1+2x/3 O 4 microwave dielectric ceramics with a spinel phase were prepared via a high-temperature solid-phase method. P–V–L theory, vibration spectra, and XPS were utilized to establish the links between the intrinsic and extrinsic factors and the microwave dielectric properties. According to the characterization, the change in permittivity ( ε r ) was ascribed to the increase in the average bond ionicity of Ti–O( Af iTi-O ) and the polar mode of the lattice vibration; the change in quality factor( Q × f ) resulted from the change in the Ti–O lattice energy ( AU Ti-O ) and existence of oxygen vacancy; the increase in temperature coefficient of the resonance frequency ( τ f ) was triggered by the increase in the Ti–O bond energy. The Li 0.6 Zn 1.1 Ti 1.3 O 4 ceramics (x = 0.45) sintered at 1125 °C finally obtained optimal microwave dielectric constants of ε r = 17.3, Q × f = 76,318 GHz and τ f = -58 ppm/°C.

Na-doped diopside microwave ceramics with dielectric properties influenced by the sintering, lattice vibration and chemical bond characteristics

The Na-doped diopside (CaMg1-xNa2xSi2O6, x = 0–0.18) microwave dielectric ceramics were fabricated via solid-state reaction method. Three phases were identified through the XRD data that was refined with the Rietveld method to obtain structural information. The role of Na+ substitution to promote the densification process could be corroborated by the SEM images and relative density. The P-V-L bond theory was used to explore the chemical bond characteristics and structure-performance relationships. Through discussion, the dielectric constant was determined by relative density rather than the bond ionicity. The Q × f value was dominated by the lattice energy, lattice vibration and was also related to the relative density and grain size. And the linear thermal expansion coefficient was closely correlated with the τf value. Excellent microwave dielectric properties, (εr = 7.573, Q × f = 35049 GHz, tan δ = 4.015 × 10−4, τf = −68.71 ppm/°C) and (εr = 7.646, Q × f = 37844 GHz, tan δ = 3.706 ×10−4, τf = −54.2 ppm/°C) were achieved for the CaMg0.97Na0.06Si2O6 ceramics sintered at 1150 °C/3 h and 1200 °C/3 h, respectively.

Effects of (Mg1/3Nb2/3)4+ substitution on the temperature-stable and low-loss (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 microwave dielectric ceramics

(Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 (x = 0.00, 0.05, 0.10, 0.13, 0.15, and 0.20) systems without additives are fabricated by facile solid-state reaction method in the air atmosphere. The influence of (Mg1/3Nb2/3)4+ substitution on microwave dielectric properties of (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 ceramics is investigated systematically. The XRD results convey that the doping ion ((Mg1/3Nb2/3)4+) should occupy (Zr0.5Ti0.5)4+ site throughout the composition. An appropriate amount of (Mg1/3Nb2/3)4+ tremendously increases the temperature stability and reduces the microwave dielectric loss of the ZrTiO4 ceramic. In addition, to further investigate the dielectric loss mechanism, high-resolution Raman mapping is used to characterize residual stresses at the grain level. The result justifies that there is non-uniform residual stress in the ceramic, which is closely related to the anharmonic vibrations of the crystal lattice and the intrinsic loss of (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 ceramics. Meanwhile, the annealing approach is applied for reducing the intrinsic loss and further improving the Q × f value. Ultimately, the optimum microwave dielectric properties with τf ∼0.8 ppm/°C, high ϵr ∼40.9 and Q × f ∼40,217 GHz are obtained in annealed (Mg1/3Nb2/3)0.13(Zr0.5Ti0.5)0.87O2 ceramic, which suggests that it can be as one of the candidates exploiting for microwave devices in 5G wireless communication technology.

Effect of Zn0·17Nb0·33Ti0·5O2 on the microwave dielectric properties of ZnTiNb2O8 ceramics

An original (1-x)ZnTiNb2O8-xZn0.17Nb0·33Ti0·5O2 (x = 0.35–0.75) composite ceramics were prepared by the traditional solid-state method. X-Ray diffraction and Raman spectroscopy results illustrated that only ZnTiNb2O8 and Zn0·17Nb0·33Ti0·5O2 were synthesized without any extra phase. The morphology and microstructures of the microwave dielectric ceramics were characterized by scanning electron microscopy and energy disperse spectroscopy. The addition of Zn0·17Nb0·33Ti0·5O2 not only effectively adjusted the τf of ZnTiNb2O8 matrix from −39.55 ppm/°C to 54.32 ppm/°C, but also significantly increased εr from −39.55 ppm/°C to 54.32 ppm/°C. But the Q × f values deteriorated from 36,914 GHz to 21,077 GHz as x increased. The ceramic with near-zero τf was synthesized at x = 0.55, meanwhile, 0.45ZnTiNb2O8-0.55Zn0·17Nb0·33Ti0·5O2 ceramic sintered at 1200 °C possessed attractive microwave dielectric properties: εr = 39.08 (6.2 GHz), Q × f = 31,384 GHz, and τf = −6.45 ppm/°C.

A novel low-loss (1-x)(Ca0.8Sr0.2)TiO3-xSmAlO3 microwave dielectric ceramics with near-zero temperature coefficient

(1-x)Ca0.8Sr0.2TiO3-xSmAlO3 (abbreviated as (1-x)CST-xSA) perovskite ceramics were synthesized through the conventional solid-state reaction process. The effects of SmAlO3 on the microstructure, low-frequency dielectric performances, and microwave dielectric properties for (1-x)CST-xSA ceramics were investigated systematically. All compositions exhibited an orthorhombic perovskite structure with dense surface morphology. With increasing the content of SmAlO3, the order of B-site cation revealed a trend of increase first and then slowly decreased. The presence of oxygen vacancies in the (1-x)CST-xSA ceramics was detected by using x-ray photoelectron spectroscopy. Excellent temperature stability of dielectric permittivity and low dielectric loss (tanδ lower than 0.005) were observed for (1-x)CST-xSA ceramics at low frequencies. For x = 0.35 composition, the temperature coefficient of the resonant frequency approached zero. In addition, the dielectric permittivity of 42.0, the quality factor of 39,120 GHz, and the temperature coefficient of resonant frequency of − 6.4 ppm/℃ were obtained for 0.65CST-0.35SA ceramics. It is suggested that (1-x)CST-xSA ceramics can be used as a candidate material for various microwave communication components.

Sintering Behavior, Phase Composition and Microwave Dielectric Characteristics of Mg4Nb2O9 Ceramics Doped with ZnO-B2O3-SiO2 Glass

The Mg4Nb2O9 doped with x mol% ZnO-B2O3-SiO2 (ZBS, 0 ≤ x ≤ 0.20) ceramics were prepared by a solid-state reaction method for developing low-fired microwave dielectric ceramics. The sintering temperatures of Mg4Nb2O9 ceramics were successfully lowered to 1100 °C by doping ZBS. With increasing x, the dielectric constant (εr ) increased from 12.3 to 13.0 and the quality factor (Q × f) decreased from 140,000 GHz to 42,580 GHz, respectively. The well microwave dielectric properties of ɛ r = 12.9, Q × f = 56470 GHz, and τf = −59.8 ppm/°C were obtained for Mg4Nb2O9-0.15 mol% ZBS ceramics.

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

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

A novel temperature-stable (1−m)Li2TiO3–mZn3Nb2O8 microwave dielectric ceramic

The novel (1 [Formula: see text]Li2TiO[Formula: see text]Zn3Nb2O8 ([Formula: see text] = 0.1, 0.16, 0.2, and 0.3) microwave dielectric ceramics were prepared by the solid-state reaction method. Phases and microstructures were analyzed by XRD and SEM, which showed the formation of Li2Zn(Ti[Formula: see text]Nb[Formula: see text]O8 solid solution instead of the coexistence of Li2TiO3 and Zn3Nb2O8. The formation of Li2Zn(Ti[Formula: see text]Nb[Formula: see text]O8 solid solution can be ascribed to the complex chemical reaction between Li2TiO3 and Zn3Nb2O8. The sintering behavior and microwave dielectric properties were investigated as functions of sintering temperatures and [Formula: see text] value. The 0.84Li2TiO[Formula: see text] 0.16Zn3Nb2O8 ceramics were well densified at 1100[Formula: see text]C and possessed excellent microwave dielectric properties with [Formula: see text] 18.05, [Formula: see text] ×[Formula: see text] [Formula: see text] 25,791 GHz (at 10.02 GHz), and a near-zero [Formula: see text] value [Formula: see text]−6.09 ppm/°C because of the function of Li2Zn([Formula: see text]Nb[Formula: see text]O8 solid solution. It provides new candidates for the field of wireless communication technology.

The relationship between crystal structure and modified microwave dielectric properties of Ca3SnSi2‐xGexO9 ceramics

AbstractCa3SnSi2‐xGexO9 (0 ≤ x ≤ 0.8) and (1–y) Ca3SnSi1.6Ge0.4O9 – y CaSnSiO5 – 2 wt% LiF (y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid‐state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge4+ replaced Si4+, and Ca3SnSi2‐xGexO9 (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge4+ substitution for Si4+ decreased the sintering temperature of Ca3SnSi2‐xGexO9 from 1425 to 1300°C, the SnO6 octahedral distortions, and the average CaO7 decahedral distortions, which affected the τf value. The large average decahedral distortions corresponded with nearer‐zero τf values at Ca3SnSi2‐xGexO9 (0.1 ≤ x ≤ 0.4) ceramics. The τf value and sintering temperature of Ca3SnSi2‐xGexO9 (x = 0.4) ceramic were adjusted to near‐zero by CaSnSiO5 and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y) Ca3SnSi1.6Ge0.4O9 – y CaSnSiO5 – 2 wt% LiF (y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: εr = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τf = ‒5.8 ppm/°C.

A novel strategy to assemble core–shell-structured LiF-CaTiO3 microwave dielectric ceramics via cold sintering and post-annealing treatment

A novel strategy to assemble core–shell-structured LiF-CaTiO3 microwave dielectric ceramics via cold sintering and post-annealing treatment

Microwave Dielectric Properties and Sintering Behavior of K20 Series Temperature‐Stable 0.91MgTiO3‐0.09(Ca0.8Na0.1Ce0.1)TiO3 Composite Ceramics

AbstractRecently, the progress of miniaturization and integration for dielectric communication devices is being motivated by the rapidly‐developed communication technology. Microwave dielectric ceramics, the foundation of dielectric communication devices, have been receiving great attention. In this study, 0.91MgTiO3‐0.09(Ca0.8Na0.1Ce0.1)TiO3 ceramic (0.91MT‐0.09CNCT) was synthesized by the traditional solid‐phase process to tune the temperature coefficient of resonant frequency (τf) to zero. Compared with 0.95MgTiO3–0.05CaTiO3 ceramic, a Q×f value increased by 15 % was achieved in 0.91MT‐0.09CNCT ceramic, meanwhile, the sintering temperature of which was significantly lowered by 225 °C. In general, the τf value is related to the (Ca0.8Na0.1Ce0.1)TiO3 content and sintering temperature. At the same time, the 0.91MT‐0.09CNCT ceramic sintered at 1175 °C has competitive dielectric properties: ϵr=20.4, Q×f=66,000 GHz, τf=0.2 ppm/°C, which suggests it a promising candidate for dielectric communication devices with low cost and green synthesis.

Chemical bond and microwave dielectric properties of two novel low-εr AGa4O7 (A = Ca, Sr) ceramics

Two novel low-εr microwave dielectric ceramics AGa4O7 (A = Ca, Sr; called CGO and SGO, respectively) were analyzed by XRD, SEM, and Raman spectroscopy, showed the monoclinic structure with a C2/c space group. Encouraging microwave dielectric properties (CGO: εr = 9.1, Q × f = 40 600 GHz (f = 12.4 GHz), and τf = −86.3 ppm °C−1; SGO: εr = 9.2, Q × f = 62 400 GHz (f = 14.6 GHz), and τf = −63.4 ppm °C−1) are obtained. The PVL chemical bond theory indicated that GaO bonds play a role in affecting the εr and Q × f values. The τf of AGa4O7 (A = Ca, Sr) had adjusted close to zero (0.93CGO-0.07CaTiO3:εr = 11.3, Q × f = 31,043 GHz, and τf = 3.97 ppm °C−1; 0.82SGO-0.18LiCa2Mg2V3O12：εr = 11.8, Q × f = 55,564 GHz, and τf = 5.62 ppm °C−1).