Influence of V2O5 Additions to 5Li2O–1Nb2O5–5TiO2 Ceramics on Sintering Temperature and Microwave Dielectric Properties

The effects of the addition of V₂O₅ on the sintering behavior, microstructure, and microwave dielectric properties of 5Li₂O–1Nb₂O₅–5TiO₂ (LNT) ceramics have been investigated. With low-level doping of V₂O₅ (≤3 wt%), the microstructure of the LNT ceramic changed from a special two-level intergrowth structure into a two-phase composite structure with separate grains. And the sintering temperature of the LNT ceramics could be lowered to around 900°C by adding a small amount of V₂O₅ without much degradation in microwave dielectric properties. Typically, better microwave dielectric properties of ɛ_r=41.7, Q × f =7820 GHz, and τ _f =45 ppm/°C could be obtained for the 1 wt% V₂O₅-doped ceramics sintered at 900°C.     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Microwave Dielectric Properties of Li2TiO3 Ceramics Doped with ZnO–B2O3 Frit

A type of new low sintering temperature ceramic, Li₂TiO₃ ceramic, has been found. Although it is difficult for the Li₂TiO₃ compound to be sintered compactly at temperatures above 1000°C for the volatilization of Li₂O, dense Li₂TiO₃ ceramics were obtained by conventional solid-state reaction method at the sintering temperature of 900°C with the addition of ZnO–B₂O₃ frit. The sintering behavior and microwave dielectric properties of Li₂TiO₃ ceramics with less ZnO–B₂O₃ frit (≤3.0 wt%) doping were investigated. The addition of ZnO–B₂O₃ frit can lower the sintering temperature of the Li₂TiO₃ ceramics, but it does not apparently degrade the microwave dielectric properties of the Li₂TiO₃ ceramics. Typically, the good microwave dielectric properties of ɛ_r=23.06, Q × f =32 275 GHz, τ_f = 35.79 ppm/°C were obtained for 2.5 wt% ZnO–B₂O₃ frit-doped Li₂TiO₃ ceramics sintered at 900°C for 2 h. The porosity was 0.08%. The Li₂TiO₃ ceramic system may be a promising candidate for low-temperature cofired ceramics applications.     

Synthesis of BaCu(B2O5) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics

BaCu(B₂O₅) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B₂O₅) phase was formed at 700°C and melted above 850°C. The BaCu(B₂O₅) ceramic sintered at 810°C had a dielectric constant (ɛ_r) of 7.4, a quality factor ( Q × f ) of 50 000 GHz and a temperature coefficient of resonance frequency (τ_f) of −32 ppm/°C. As the BaCu(B₂O₅) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B₂O₅) was added to the Ba(Zn_1/3Nb_2/3)O₃ (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B₂O₅) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q × f =16 000 GHz, ɛ_r=35, and τ_f=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B₂O₅) ceramic sintered at 875°C for 2 h.     

Microwave Dielectric Properties and Chemical Resistance of Low-Temperature-Sintered CaZrB2O6 Ceramics

Dolomite-type borate ceramics consisting of CaZrB₂O₆ were synthesized via a conventional solid-state reaction route; low-temperature sintering was explored using Bi₂O₃–CuO additives of 1–7 wt% for low-temperature co-fired ceramics applications. For several sintering temperatures, the microwave dielectric properties and chemical resistance of the ceramics were investigated. The CaZrB₂O₆ ceramics with 3 wt% Bi₂O₃–CuO addition could be sintered below 925°C, and the microwave dielectric properties of the low-temperature samples were ɛ_r=10.55, Q × f =87,350 GHz, and τ_f=+2 ppm/°C. The chemical resistance test result showed that both CaZrB₂O₆- and Bi₂O₃–CuO-added CaZrB₂O₆ ceramics were durable in basic solution but were degraded in acid solution.     

Sintering and Microwave Dielectric Properties of the LiNb0.63Ti0.4625O3 Ceramics with the B2O3–SiO2 Liquid-Phase Additives

The effect of B₂O₃–SiO₂ liquid-phase additives on the sintering, microstructure, and microwave dielectric properties of LiNb_0.63Ti_0.4625O₃ ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the densification and dielectric properties of LiNb_0.63Ti_0.4625O₃ ceramics could be greatly improved by adding a small amount of B₂O₃–SiO₂ solution additives. No secondary phase was observed for the ceramics with B₂O₃–SiO₂ additives. With the addition of 0.10 wt% B₂O₃–SiO₂, the ceramics sintered at 900°C showed favorable microwave dielectric properties with ɛ_r=71.7, Q × f =4950 GHz, and τ_f=−2.1 ppm/°C. The energy dispersive spectra analysis showed an excellent co-firing interfacial behavior between the LiNb_0.63Ti_0.4625O₃ ceramic and the Ag electrode. It indicated that LiNb_0.63Ti_0.4625O₃ ceramics with B₂O₃–SiO₂ solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.     

Microwave Dielectric Properties of Low-Fired Ba5Nb4O15

The effect of B₂O₃ on the sintering temperature and microwave dielectric properties of Ba₅Nb₄O₁₅ has been investigated using X-ray powder diffraction, scanning electron microscopy, and a network analyzer. Interactions between Ba₅Nb₄O₁₅ and B₂O₃ led to formation of second phases, BaNb₂O₆ and BaB₂O₄. The addition of B₂O₃ to Ba₅Nb₄O₁₅ resulted in lowering the sintering temperature from 1400° to 925°C. Low-fired Ba₅Nb₄O₁₅ could be interpreted by measuring changes in the quality factor ( Q × f ), the relative dielectric constant (ɛ_r), and the temperature coefficient of resonant frequency (τ_f) as a function of B₂O₃ additions. More importantly, the formation of BaNb₂O₆ provided temperature compensation. The microwave dielectric properties of low-fired Ba₅Nb₄O₁₅ had good dielectric properties: Q × f = 18700 GHz, ɛ_r= 39, and τ_f= 0 ppm/°C.     

Microwave Dielectric Properties of Low-Fired ZnNb2O6 Ceramics with BiVO4 Addition

The BiVO₄ additive was found effective for low-temperature firing of ZnNb₂O₆ polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO₄-doped ZnNb₂O₆ samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q · f = 55000 GHz, ɛ_r= 26, and τ_f=−57 ppm/°C. With increasing BiVO₄ addition up to 20 mol% relative to ZnNb₂O₆, while the quality factor Q · f was gradually decreased, the relative dielectric constant, ɛ_r, was linearly increased and the temperature coefficient of resonant frequency, τ_f, was slightly increased. The variations in Q · f and ɛ_r are surely attributable to the residual BiVO₄ in the ZnNb₂O₆ matrix. An unexpected slight increase in τ_f is probably due to the formation of the Bi(V,Nb)O₄-type solid solution.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Glass-Free Zn2Te3O8 Microwave Ceramic for LTCC Applications

A Zn₂Te₃O₈ ceramic was investigated as a promising dielectric material for low-temperature co-fired ceramics (LTCC) applications. The Zn₂Te₃O₈ ceramic was synthesized using the solid-state reaction method by sintering in the temperature range 540°–600°C. The structure and microstructure of the compounds were investigated using X-ray diffraction (XRD) and scanning electron microscopy methods. The dielectric properties of the ceramics were studied in the frequency range 4–6 GHz. The Zn₂Te₃O₈ ceramic has a dielectric constant (ɛ_r) of 16.2, a quality factor ( Q _u× f ) of 66 000 at 4.97 GHz, and a temperature coefficient of resonant frequency (τ_f) of −60 ppm/°C, respectively. Addition of 4 wt% TiO₂ improved the τ_f to −8.7 ppm/°C with an ɛ_r of 19.3 and a Q _u× f of 27 000 at 5.14 GHz when sintered at 650°C. The chemical reactivity of the Zn₂Te₃O₈ ceramic with Ag and Al metal electrodes was also investigated.     

Formation and Microwave Dielectric Properties of the Mg2V2O7 Ceramics

The formation process and microwave dielectric properties of the Mg₂V₂O₇ ceramics were investigated. The MgV₂O₆ phase that was formed at around 450°C interacted with remnant MgO above 590°C to form a homogeneous monoclinic Mg₂V₂O₇ phase. Finally, this monoclinic Mg₂V₂O₇ phase was changed to a triclinic Mg₂V₂O₇ phase for the specimen fired at 800°C. Sintering at 950°C for more than 5 h produced high-density triclinic Mg₂V₂O₇ ceramics. In particular, the Mg₂V₂O₇ ceramics sintered at 950°C for 10 h exhibited the good microwave dielectric properties of ɛ_r=10.5, Q × f =58 275 GHz, and τ_f=−26.9 ppm/°C.     

Synthesis and Microwave Dielectric Properties of Re3Ga5O12 (Re: Nd, Sm, Eu, Dy, Yb, and Y) Ceramics

Re₃Ga₅O₁₂ (Re: Nd, Sm, Eu, Dy, Yb, and Y) garnet ceramics were synthesized and their microwave dielectric properties were investigated for advanced substrate materials in microwave integrated circuits. The Re₃Ga₅O₁₂ ceramics sintered at 1350°–1500°C had a high-quality factor ( Q × f ) ranging from 40 000 to 192 173 GHz and a low-dielectric constant (ɛ_r) of between 11.5 and 12.5. They also exhibited a relatively stable temperature coefficient of resonant frequency (τ_f) in the range of −33.7 to −12.4 ppm/°C. In particular, the Sm₃Ga₅O₁₂ ceramics sintered at 1450°C exhibited good microwave dielectric properties of ɛ_r=12.4, Q × f =192 173 GHz, and τ_f=−19.2 ppm/°C.     

Tailoring the Microwave Dielectric Properties of MgNb2O6 and Mg4Nb2O9 Ceramics

The columbites MgNb₂O₆, MgTa₂O₆, and corundum-type Mg₄Nb₂O₉ ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the sintered samples were investigated by X-ray diffraction and scanning electron microscopic techniques. The microwave dielectric properties of the samples were measured by the resonance method in the frequency range 4–6 GHz. The dielectric properties have been tailored by forming a solid solution between MgNb₂O₆ and MgTa₂O₆ and by the substitution of TiO₂ for Nb₂O₅ in both MgNb₂O₆ and Mg₄Nb₂O₉ ceramics. The Mg(Nb_0.7Ta_1.3)O₆ has ɛ_r=29, Q _u× f =67 800 GHz, and τ_f=0.8 ppm/°C and the MgO–(0.4)Nb₂O₅–(1.5)TiO₂ composition has ɛ_r=34.5, Q _u× f =81 300 GHz, and τ_f=−2 ppm/°C.     

Effect of Li2CO3 Addition on the Sintering Temperature and Microwave Dielectric Properties of Mg2V2O7 Ceramics

Li₂CO₃ was added to Mg₂V₂O₇ ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li₂CO₃ changed the crystal structure of Mg₂V₂O₇ ceramics from triclinic to monoclinic. The 6.0 mol% Li₂CO₃-added Mg₂V₂O₇ ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛ _r=8.2, Q × f =70 621 GHz, and τ_f=−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li₂CO₃-added Mg₂V₂O₇ ceramic at 800°C. Therefore, this ceramic is a good candidate material in low-temperature co-fired ceramic multilayer devices.     

Sintering Behavior and Dielectric Properties of Bi3NbO7 Ceramics Prepared by Mixed Oxides and High-Energy Ball-Milling Methods

The sintering behavior and dielectric properties of Bi₃NbO₇ ceramics prepared by the high-energy ball milling (HEM) method and conventional mixed oxides method with V₂O₅ addition were investigated. All the samples were sintered between 840° and 960°C. For the ceramics prepared by the mixed oxides method, the pure tetragonal Bi₃NbO₇ phase formed without any cubic phase. With changing sintering temperature, the dielectric constant ɛ_r lies between 79 and 92, while the Q × f values are between 300 and 640 GHz. The samples sintered at 870°C have the best microwave dielectric properties with ɛ_r=79, Q × f =640 GHz, and the temperature coefficients of resonant frequency τ_f between 0 and −20 ppm/°C. For the ceramics prepared by the HEM, a pure cubic phase was obtained. The ɛ_r changes between 78 and 80 and Q × f were between 200 and 290 GHz.     

Effect of Bi2O3 Addition on the Sintering Temperature and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Bi₂O₃ was added to a nominal composition of Zn_1.8SiO_3.8 (ZS) ceramics to decrease their sintering temperature. When the Bi₂O₃ content was <8.0 mol%, a porous microstructure with Bi₄(SiO₄)₃ and SiO₂ second phases was developed in the specimen sintered at 885°C. However, when the Bi₂O₃ content exceeded 8.0 mol%, a liquid phase, which formed during sintering at temperatures below 900°C, assisted the densification of the ZS ceramics. Good microwave dielectric properties of Q × f =12,600 GHz, ɛ_r=7.6, and τ_f=−22 ppm/°C were obtained from the specimen with 8.0 mol% Bi₂O₃ sintered at 885°C for 2 h.     

Modification of MgAl2O4 Microwave Dielectric Ceramics by Zn Substitution

MgAl₂O₄ microwave dielectric ceramics were modified by Zn substitution for Mg, and their dielectric characteristics were evaluated, along with their structures. Dense (Mg_{1− x} Zn _x )Al₂O₄ ceramics were obtained by sintering at 1550°–1650°C in air for 3 h, and the (Mg_{1− x} Zn _x )Al₂O₄ solid solution was determined in the entire composition range. With Zn substitution for Mg, the dielectric constant ɛ of MgAl₂O₄ just varied from 7.90 to 8.56, while the Q × f value had significantly improved up to a maximal value of 106 000 GHz at x =1.0. Moreover, the τ_f of MgAl₂O₄ ceramics had declined from −73 to −63 ppm/°C.     

BiNbO4-Based Glass–Ceramic Composites for Microwave Applications

The effect of a bespoke glass sintering aid, 0.3Bi₂O₃–0.3Nb₂O₅–0.3B₂O₃–0.1SiO₂ (BN1), developed from the base ceramic composition, BiNbO₄ (BN), on the sinterability, microstructure, and microwave (MW) dielectric properties of BN ceramics has been investigated. Densities >97% theoretical could be achieved at 1020°C for samples with up to 15% BN1 additions. The resulting microstructure was composed of BN laths surrounded by a residual glass phase that contained small fibrous crystals. Some evidence of dissolution of BN crystals was observed. Optimum properties were exhibited for samples with 15 wt% of glass addition sintered for 4 h at 1020°C with a relative permittivity ɛ_r=38, a MW quality factor Q × f ₀=17 353 at 5.6 GHz, and a temperature coefficient of resonant frequency τ_f=−10 ppm/°C. The high Q × f ₀, ɛ_r, and low τ_f, coupled with a relatively low sintering temperature, suggest that the use of bespoke glass sintering aids of this type may have great potential for the fabrication of MW ceramics.     

Characteristics of High-Q Microwave Dielectric Ceramics Nd(Co1/2Ti1/2)O3 With CuO Addition

We report the microwave dielectric properties and the microstructures of Nd(Co_1/2Ti_1/2)O₃ ceramics prepared by the conventional solid-state route. The prepared Nd(Co_1/2Ti_1/2)O₃ exhibits a mixture of Co and Ti showing a 1:1 order in the B site. Lowering the sintering temperature (as low as 1260°C) and promoting the densification of Nd(Co_1/2Ti_1/2)O₃ ceramics could be effectively achieved by adding CuO (up to 0.75 wt%). At 1350°C, Nd(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% CuO addition possess a dielectric constant (ɛ_r) of 27.6, a Q × f value of 165 000 GHz (at 9 GHz), and a temperature coefficient of resonant frequency (τ_f) of −20 ppm/°C. By comparing with pure Nd(Co_1/2Ti_1/2)O₃ ceramics, incorporating additional CuO helps to render a dielectric material with a higher dielectric constant, a smaller τ_f value, and a 20% dielectric loss reduction, which makes it a very promising candidate for applications requiring low microwave dielectric loss.     

Microwave Dielectric Properties of La6Mg4A2W2O24 [A=Ta and Nb] Ceramics

The microwave dielectric properties of two A-site-deficient perovskite-type ceramics in the La₆Mg₄A₂W₂O₂₄ [A=Ta and Nb] system were investigated. The compounds were synthesized by the solid-state ceramic route. The structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. The dielectric properties were measured in the microwave frequency range [4–6 GHz] by the resonance method. La₆Mg₄Ta₂W₂O₂₄ had Q _u× f =13 600 GHz, ɛ_r=25.2, and τ_f=−45 ppm/°C and La₆Mg₄Nb₂W₂O₂₄ had Q _u× f =16 400 GHz, ɛ_r=25.8, and τ_f=−56 ppm/°C.