Influence of CuO addition to BaSm2Ti4O12 microwave ceramics on sintering behavior and dielectric properties

Microwave dielectric ceramics of tungsten–bronze-type BaSm₂Ti₄O₁₂ were prepared by doping CuO (up to 2 wt.%) as the liquid-phase sintering aid. The effects of CuO additive on the densification, micro structure and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of BaSm₂Ti₄O₁₂ ceramics with 1 wt.% CuO addition can be effectively reduced to 1160 °C, about 200 °C lower than that of pure BaSm₂Ti₄O₁₂ ceramics, while good microwave dielectric properties of ɛ_r = 75.8, Q*f = 4914.6 GHz and τ_f = −7.65 ppm/°C were still achieved.     

Effects of CaF2 addition on sintering behavior and microwave dielectric properties of ZnTa2O6 ceramics

Microwave dielectric ceramics ZnTa₂O₆ were prepared by conventional mixed oxide route. The effects of CaF₂ addition on the microstructures and microwave dielectric properties of ZnTa₂O₆ ceramics were investigated. Formation of second phase can be detected at the high addition of CaF₂ (0.5–1.0 wt.%). Variation of grain shapes were observed with CaF₂ content increasing. The sintering temperature of CaF₂-doped ZnTa₂O₆ ceramics can be effectively lowered from 1400 °C to 1225 °C due to liquid phase effect. The microwave dielectric properties were affected by the amount of CaF₂ addition. At 1225 °C for 4 h, ZnTa₂O₆ ceramics with 0.25 wt.% CaF₂ possesses excellent microwave dielectric properties: ε_r = 31.32, Q × ? = 73600 GHz(6.8 GHz) and τ_? = ? 6.97 ppm/°C.     

Effect of sintering temperature and time on microwave dielectric properties of CaNb2O6 ceramics

The microwave dielectric properties of CaNb₂O₆ ceramics were investigated with a view to their application in mobile communication. The CaNb₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures and sintering times. A maximum density of 4.67 g/cm³ was obtained for CaNb₂O₆ ceramic, sintered at 1,400 °C for 4 h. Dielectric constants (ε _r ) of 13.3–18.1 and quality factor (Q × f) of 12,200–50,000 GHz were obtained at sintering temperatures in the range 1,300–1,500 °C for 4 h. Dielectric constants (ε _r ) of 18.0–18.1 and quality factor (Q × f) of 44,300–50,000 GHz were obtained for sintering times in the range 2–6 h at a sintering temperature of 1,400 °C. A dielectric constant (ε _r ) of 18.1, a quality factor (Q × f) of 50,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?54 ppm/°C were obtained when CaNb₂O₆ ceramics were sintered at 1,400 °C for 4 h.     

Mg4(Ta1-xVx)2O9陶瓷的烧结特性和微波介电性能

用固相法制备了一系列Mg4(Ta1-xVx)2O9(MTV)陶瓷,研究了V5 取代Ta5 、MTV陶瓷的烧结特性和微波介电性能.用XRD和SEM研究其晶体结构和微观形貌.结果表明:在组分x≤0.3范围内形成了Mg4(Ta1-xVx)2O9连续固溶体.少量V5 取代Ta5 能够使MTV陶瓷的烧结温度从1450℃降至1150℃,但同时品质因数降低.x=0.1,1150℃烧结的Mg4(Ta1-0.1V0.1)2O9陶瓷具有较好的微波介电性能:ε约为11,Q·f值达41000GHz(8GHz).     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Low temperature sintering and microwave dielectric properties of MgNb2O6 ceramics

The effects of co-doped CuO and B₂O₃ addition on the sintering temperature, microstructure and microwave dielectric properties of MgNb₂O₆ ceramics prepared with conventional solid-state route were investigated. When both CuO and B₂O₃ were added, the MgNb₂O₆ ceramics were not only sintered at 1000 °C but also improved the Qf value. MgNb₂O₆ ceramics can be well sintered to approach to 98.1% theoretical density with 2.0 wt.% CuO–B₂O₃ additive due to its liquid phase effect. With 2.0 wt.% CuO–B₂O₃, a dielectric constant of 21.5, a Qf value of 108,000(GHz) and a τ _f value of −44 ppm/°C of MgNb₂O₆ ceramics doped with CuO–B₂O₃ sintered at 1050 °C for 2 h are obtained. The variation of ε _r, Qf and τ _f were also explained based on the difference in microstructures.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Influence of V2O5 additions to Ba(Mg1/3Ta2/3)O3 ceramics on sintering behavior and microwave dielectric properties

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg_1/3Ta_2/3)O₃ exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V₂O₅ (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg_1/3Ta_2/3)O₃ ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V₂O₅ addition. The detected second phase Ta₂O₅ was mainly the result of V⁵⁺ substitution in the ceramics. Dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V₂O₅ addition due to the increase in B-site ordering. The ε_r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τ_f value of 7.2 ppm/°C were obtained for Ba(Mg_1/3Ta_2/3)O₃ ceramics with 0.25 wt.% V₂O₅ addition sintered at 1500 °C for 3 h.     

ZnO掺杂对CLST微波介质陶瓷烧结及介电性能的影响

研究了烧结助剂ZnO对CaO-Li2O-Sm2O3-TiO2(简写为CLST)系微波介质陶瓷的烧结特性及介电性能的影响.结果表明:ZnO的添加能有效地降低CLST陶瓷的烧结温度至1150℃.掺杂2wt%ZnO的CLST陶瓷取得了较好的介电性能:εr=84,tanδ=0.009,τf=-15ppm/℃.     

Low-temperature firing and microwave dielectric properties of MgTiO3 ceramics with Bi2O3–V2O5

The effects of Bi₂O₃–V₂O₅ additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃ Ceramics were investigated. The Bi₂O₃–V₂O₅ addition lowered the sintering temperature of MgTiO₃ ceramics effectively from 1400 to 875 °C due to the liquid-phase effect. The microwave dielectric properties were found to strongly correlate with the amount of Bi₂O₃–V₂O₅ addition. The saturated dielectric constant decreased and the maximum Qf values increased with the increasing V₂O₅ content, which is attributed to the variation of the second phase including Bi₂Ti₂O₇, Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. At 875 °C, MgTiO₃ ceramics with 5.0 mol% Bi₂O₃–7 mol% V₂O₅ gave excellent microwave dielectric properties: ε_r = 20.6,Qf = 10420 GHz (6.3 GHz).     

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Ca₂Ce₂Ti₅O₁₆ dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO₂ and another unidentified phase (that vanished at ? 1400 °C) as secondary phases along with the parent Ca₂Ce₂Ti₅O₁₆ phase. The amount of the parent Ca₂Ce₂Ti₅O₁₆ phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ? _r and Q _u f _o increased with sintering temperature. An ? _r ～ 81.5, Q _u f _o ～ 5915 GHz and τ _f ～ 219 GHz were achieved for the sample sintered at 1450 °C.     

Preparation and microwave dielectric properties of Bi2Ti4O11 ceramics

Single phase of Bi₂Ti₄O₁₁ ceramics, which belong to meta-stable phase compounds, were synthesized by controlling the reaction time through conventional solid-state method. The effects of annealing time on phase composition of Bi₂Ti₄O₁₁ ceramic powders and sintered ceramics were studied by XRD analysis. Second phase Bi₂Ti₂O₇ appeared when the annealing time shorter than 4 h. However, pure phase of Bi₂Ti₄O₁₁ powders can be formed by prolonging the annealing time to 6 h at 1,000 °C. The sintering temperatures on microstructure and microwave dielectric properties of Bi₂Ti₄O₁₁ ceramics were investigated. The results show that ceramics sintered at 1,075–1,175 °C are single phase of Bi₂Ti₄O₁₁ and present two different sizes of prismatic shape grains. Smaller size crystals grow into larger ones with increasing sintering temperature. The ceramics sintered at 1,125 °C reach a maximum density and have a microwave dielectric properties of ε_r = 51.2, Q × f = 3,050 GHz and τ_f = ?297 ppm/°C.     

Low temperature sintering and microwave dielectric properties of Ba4Sm9.33Ti18O54 ceramics

The effect of BaCu(B₂O₅) (BCB) on the sinterability, microstructure and microwave dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) has been investigated. Dilatometric measurements reveal that the sintering temperature of BST can be reduced by the addition of BCB. Microstructural analysis shows abnormal grain growth with large amount of BCB. A ceramic composite with Q × f = 4000 GHz, ?_r = 52 and τ_f = ?29 ppm/°C which can be sintered at 950 °C is obtained when 10 wt% BCB is added to BST. EDS analysis shows that the composite is chemically compatible with silver.     

Reduction in sintering temperature and tunable microwave dielectric properties in NaCa4V5O17 via compositional engineering

Some Li⁺-substituted NaCa₄V₅O₁₇ ceramics were designed and fabricated by the solid-state reaction method. Effects of cation doping on the sintering behavior, crystal structure, microstructure, and dielectric properties were systematically studied. As expected, Li⁺ substitution effectively reduced the densification temperature of NaCa₄V₅O₁₇ ceramics and lower the relative permittivity (ε_r), but surprisingly increased the quality factor (Q×f). A composition with 20?mol% Li⁺ dopants exhibits the highest Q×f?=?66,000?±?124?GHz coupled with an ε_r of 10.4?±?0.1 and a τ_f of ? 81.3?±?1.4?ppm/°C. Such compositional dependence in dielectric properties was analyzed in terms of ionic polarization and packing fraction.

     

Electrical and magnetic properties of Mg0.85Co0.15Fe2O4 ceramics with V2O5 additives

In this study, magnesium-cobalt ferrite (Mg_0.85Co_0.15Fe₂O₄) powder was synthesized using a solid-state synthesis method, followed by the liquid sintering using 0.50–3.00 wt% vanadium oxide (V₂O₅) at 1050 °C for 2 h. X-ray diffraction (XRD) studies confirmed the formation of spinel ferrite. Microstructure studies revealed that by increasing the amount of V₂O₅ from 0.50 to 3.00 wt%, the average grain size was reduced from 15.9?±?5.9 to 7.0?±?2.5 μm and the samples were highly densified. V₂O₅ promoted the sintering process and reduced the dielectric constant (ε′), loss tangent (tanδ), and increased electrical resistivity. A magnesium-cobalt ferrite sample with 25.4 dielectric constant, 0.078 loss tangent, and 9.0?×?10⁵ Ω.cm resistivity at 1 MHz was achieved using 3.00 wt% V₂O₅. Increasing V₂O₅ content caused increasing coercivity (Hc) from 89 to 129 Oe. Moreover, the maximum saturation magnetization (Ms) value of 26.8 emu/g was obtained for the sample containing 1.50 wt% V₂O₅. The small dielectric loss tangent of the samples at 1 MHz suggests applications of these ceramics in microwave devices.