Microwave dielectric properties of low-firing BiNbO4 ceramics with V2O5 substitution

The effect of V₂O₅ substitution on the sintering behavior and the microwave dielectric properties of BiNbO₄ ceramics were studied. The sintering temperatures of Bi(V _x Nb_1?x )O₄ ceramics decrease from 990 to 810°C with x value increasing from 0.002 to 0.064. The size of grains increased with the sintering temperature increasing and decreased with the substitution amount increasing. The dielectric properties are affected by the microstructures very much. The quality factor Q value is from 2500 to 4000 at about frequency?=?5 GHz and reach to the maximum when x?=?0.032. With the different x value, the Q _f values change between 15000 to 20000 GHz; the τ _f values changes between 0 and +20 ppm/°C between temperature range 25～85°C and decreased with the increasing of x value.     

Liquid phase effect of La2O3 and V2O5 on microwave dielectric properties of Mg2TiO4 ceramics

Dielectric ceramics of Mg₂TiO₄ (MTO) were prepared by solid-state reaction method with 0.5–1.5 wt.% of La₂O₃ or V₂O₅ as sintering aid. The influences of La₂O₃ and V₂O₅ additives on the densification, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that La₂O₃ and V₂O₅ additives lowered the sintering temperature of MTO ceramics to 1300 °C and 1250 °C respectively, whereas the pure MTO exhibits highest density at 1400 °C. The reduction in sintering temperature with these additives was attributed to the liquid phase effect. The average grain sizes of the MTO ceramics added with La₂O₃, and V₂O₅ found to decrease with an increase in wt%. The dielectric constant (ε_r) was not significantly changed, while unloaded Q values were affected with these additives, and the values were in the range of 92,000–157,550 GHz and 98,000–168,000 GHz with the addition of La₂O₃ and V₂O₅, respectively. The dielectric properties are strongly dependent on the densification and the microstructure of the MTO ceramics. The decrease in Q×f _o value at higher concentration of La₂O₃ and V₂O₅ addition was owing to inhomogeneous grain growth and the liquid phase which is segregated at the grain boundary. In comparison with pure MTO ceramics, La₂O₃ and V₂O₅ additives effectively improved the densification and dielectric properties with lowering of sintering temperature. The proposed loss mechanisms suggest that the oxygen vacancies and the average grain sizes are the influencing factors in the dielectric loss of MTO ceramics.     

Low-temperature sintering and microwave dielectric properties of Mg4Nb2O9 ceramics

The effects of V₂O₅ and Li₂CO₃ on the sinterability and microwave dielectric properties of Mg₄Nb₂O₉ (MN) ceramics were investigated. With addition of 1.5wt% V₂O₅, the dielectric constant (?) and Q·? value of MN ceramics sintered at 1,000 °C are comparable to those of pure MN sintered at 1,400 °C. The good results are because of the enhancement of the density by liquid sintering at the lower temperatures. With the mixtures of V₂O₅ and Li₂CO₃, the sintering temperature of MN was further reduced to 925 °C at the expense of the quality factor (Q·?) value. Typically, ? of 13.7 and Q·? value of 78,000 GHz were obtained for the specimens with mixtures of 1.5wt% V₂O₅ and 1.5wt% Li₂CO₃ and sintered at 925 °C for 5 h.     

The sintering behavior and microwave dielectric properties of Mg4(Nb,Sb)2O9 ceramics

The sintering behavior, microstructure and microwave dielectric properties of Mg₄(Nb_2?x Sb _x )O₉ (0?≤?x?≤?2) solid solutions were investigated systematically by X-ray diffraction(XRD), scanning electron microscopy(SEM) and a network analyzer. The solid solutions of Mg₄(Nb_2?x Sb _x )O₉ was formed with x value being no more than 1.6. The dielectric constant (?) of the sintered ceramics decreased from 13.06 to 6.28 with Sb content x from 0 to 1.6. With a substitution of Sb⁵⁺ for Nb⁵⁺ (0.04?≤?x?≤?0.08), the sintering temperature of Mg₄Nb₂O₉ ceramics was decreased from 1400 to 1300 °C without degradation of the Qf values. The optimum microwave dielectric properties of ??～?12.26, Qf?～?168,450 GHz, and τ _f?～??56.4 ppm/°C were obtained in the composition of Mg₄(Nb_1.6Sb_0.4)O₉ sintered at 1300 °C.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C     

Preparation and property of BaTi2O5 ceramics by arc-melting and spark plasma sintering

In the present study, a new procedure, arc-melting followed by spark plasma sintering, was employed to prepare BaTi₂O₅ ceramics with high relative density and large dimension. Single-phased BaTi₂O₅ powders were synthesized from BaCO₃ and TiO₂ powders by arc-melting, and then the BaTi₂O₅ powders were densified by spark plasma sintering at different temperatures (1273-1473?K) and pressures (20-50?MPa). Single-phased BaTi₂O₅ ceramic was obtained at and below 1423?K, however, it tended to decompose at elevated temperatures. Considering the upperbound decomposing temperature, we further enhanced the densification of BaTi₂O₅ ceramics by increasing the sintering pressure, and a high relative density of 92.1?% was achieved at 50?MPa. The permittivity of the BaTi₂O₅ ceramics was 28.7 at 1?MHz, and increased with the measuring temperature, reaching a maximum value of 191 at the Curie temperature of?~?740?K.     

Effects of V2O5 addition on the phase-structure and dielectric properties of zinc titanate ceramics

V₂O₅-doped zinc titanate ceramics (ZnTiO₃) were prepared by conventional mixed-oxide method combined with a semi-chemical processing. The effects of V₂O₅ addition on the phase-structures and the dielectric properties of ZnTiO₃ ceramics were investigated. The results show the sintering temperature of zinc titanate ceramics could be lowered from 1,150 to 930 °C by reducing the size of starting powders using a semi-chemical processing; and with adding V₂O₅ addition, the densification temperature of ZnTiO₃ ceramics could be reduced to 875 °C. Also the phase transition temperature from hexagonal ZnTiO₃ phase to cubic Zn₂TiO₄ was lowered by adding V₂O₅. The best properties were: ? _r?=?20.6, $ Q \times f = 8,873\;{\text{GHz}} $ , when the ceramics was sintered at 900 °C, which is a promising candidate in the field of multi-layer devices requiring low sintering temperature (≤900 °C).     

正极材料V2O5的研究进展

综述了近年来锂离子电池正极材料V2O5的不同制备方法与V2O5的结构、电化学性能的关系,重点阐述了用低温法(溶胶-凝胶法)制备非晶态V2O5(包括干凝胶、气凝胶、类气凝胶).     

Thermoelectric Ca3Co4O9 ceramics consolidated by Spark Plasma sintering

Hole-doped Ca₃Co₄O₉ (Co349) ceramics were prepared using solid-state reaction. Two processing strategies have been used to produce the thermoelectric oxide ceramics, Conventional and Spark Plasma (SPS) Sintering to control the grains consolidation, texturation and sample densification. Thermoelectric properties were measured and the influence of the processing conditions on the properties was evidenced. SPS favours shorter elaboration times and produces samples with larger thermoelectric properties due to better densification and alignment. The effect of the free deformation and texturation using the SPS technique is discussed. Seebeck coefficient values of 180 μV/K at 873 K are obtained.     

Effect of microwave sintering on structural, morphological and dielectric properties of Ba(FeNb)0.5O3 ceramics

Polycrystalline Ba(FeNb)_0.5O₃/BFN ceramics were sintered conventionally and in a microwave (MW) furnace, respectively. Conventional and microwave sintering temperatures were same with different soaking times. Microwave sintering of BFN ceramics showed enhanced grain growth with improved dielectric properties. Highest dielectric constant (~29,913 at 1 kHz) at room temperature (RT) was observed in BFN ceramics sintered in MW furnace for 30 min. At RT, a non-Debye type of dielectric relaxation was observed in both conventionally and MW sintered BFN ceramics. The observed giant dielectric constant of conventionally and MW sintered BFN ceramics was attributed to intrinsic (space charge polarization) and extrinsic (Maxwell-Wagner type polarization) effects, respectively.     

Self-constrained sintering of Al2O3/glass/Al2O3 ceramics by glass infiltration

Though need for precise alignment of interlayer patterning in LTCC application, there have been few reports about zero-shrinkage sintering techniques. In this study, ceramic substrate with minimal x–y shrinkage was prepared by glass infiltration method with ‘Al₂O₃/glass/Al₂O₃’ structure. Glass infiltration into alumina particle layer was observed with variation of both sintering temperature (700?≤?T _sint.?≤?900 °C) and alumina particle size distribution (0.5?≤?D ₅₀?≤?1.8 μm). Since glass had low viscosity enough to infiltrate at 700 °C, infiltration started at that temperature and infiltrated up to 20 μm or so with temperature increase, but infiltration depth did not increase noticeably above 750 °C. Based on these results, when sintered at 900 °C with controlled sheet thickness of both glass and alumina, the shrinkage in x–y direction was calculated as less than 0.2%, with 40% in z direction. Dielectric constant (? _r) measured 6.19 with quality factor (Q) of 552 at 1 GHz of frequency. From these results, it is thought that zero-shrinkage ceramic substrates would be obtained without de-lamination.     

Effect of Zn2SnO4 on the sintering and electrical properties of SnO2 ceramics

SnO₂ ceramics with relative density about 98 % were obtained based on the addition of Zn₂SnO₄. The shrinkage of the ceramic samples increased sharply and got a saturated value about 13.3 % with doping more than 0.2 mol% Zn₂SnO₄. In the dielectric spectra, no relaxation peaks were observed and no deep trap states could be detected from 50–300 °C and 40–5 M?Hz. Thus, the oxygen vacancies may not be necessary for the densification of SnO₂ ceramics during sintering process. For all the samples, nonlinear electrical properties were observed and the breakdown electrical fields are in good agreement with the barrier height. With increasing Zn₂SnO₄ content, the activation energies E _a for O^? or O^2? adsorbed at grain boundary decreased and the doping of Zn₂SnO₄ may be an important reason for the improve of grain conductivity and formation of Schottky barrier.     

Crystal structure and the effect of annealing atmosphere on the dielectric properties of the spinels MgAl2O4, NiFe2O4, and NiAlFeO4

The non-transition metal spinel MgAl₂O₄ and the transition metal spinels (NiFe₂O₄, NiAlFeO₄) have been prepared by standard ceramic processing method in the air. The effect of annealing atmosphere on the dielectric properties after sintering has been studied. The annealing atmospheres were N₂, O₂, and N₂–H₂ mixture. Dielectric constant ? _r and tangent loss tanδ have been characterized by varying the measuring temperature and frequency (5 Hz–5 MHz) using the impedance analyzer. The ? _r and tanδ of the non-transition metal spinel MgAl₂O₄ remained unchanged even with varying the annealing atmosphere. While the dielectric properties of the transition metal spinels, NiFe₂O₄ and NiAlFeO₄ were critically dependent on the annealing atmosphere. Crystal structural models for the samples manufactured in air have been tested by the Rietveld refinement method for both the centrosymmetric Fd-3m and the noncentrosymmetric F-43m. The electron density distributions were determined by the whole pattern fitting based on the maximum entropy method (MEM). The dielectric properties of the samples have been also discussed in terms of the structure and electron distribution analysis results.     

Structural and microwave dielectric properties of Ba5-xLaxTixNb4-xO15 ceramics

The structural and microwave dielectric properties of Ba_5?x La _x Ti _x Nb_4?x O₁₅ (1?≤?x?≤?3) was investigated. The single phase with A₅B₄O₁₅-type cation-deficient hexagonal perovskite structure was obtained over the whole composition range. These ceramics have high dielectric constant up to 56, high quality factors (Q?×?f ) up to 35,000, and low temperature coefficient of resonant frequencies (τ _f ) in the range +69 to ?3 ppm °C^?1. The dielectric constants and τ _f of these ceramics gradually decrease parallel to an increase in B-site bond valence with increasing La and Ti content.     

Electrical and optical characterization of Ag2V4O11 and Ag4V2O6F2

The two silver vanadium oxide phases—Ag₂V₄O₁₁ and Ag₄V₂O₆F₂—were prepared by hydrothermal synthesis. The electrical conductivity of both silver vanadate powders was determined by the powder-solution-composite (PSC) method. The conductivities obtained were 0.0085 ± 0.0005 and 0.0005 ± 0.00015 S/cm for the Ag₂V₄O₁₁ and Ag₄V₂O₆F₂, respectively, the first such report for the Ag₄V₂O₆F₂ phase. The optical gap and the transmission where studied by diffuse reflectance. Both were larger for Ag₄V₂O₆F₂ than Ag₂V₄O₁₁, concomitant with a decrease in carrier content.     

烧结工艺对纳米Li4Ti5O12性能的影响

以醋酸锂和钛酸四丁酯为原料、冰醋酸和无水乙醇为水解抑制剂和溶剂,采用溶胶-凝胶法经高温烧结制备了纳米Li4Ti5O12负极材料,系统研究了烧结工艺对材料组成、结构和电化学性能的影响.研究表明,烧结温度是影响材料性能的最主要因素,恒温时间次之.采用两步烧结法,将所得前驱体以5C/min的速率升温到600℃,保温6h,然后...     

V2O5含量对Bi2O3-V2O5复合添加NiCuZn铁氧体性能的影响

用传统陶瓷工艺制配了(Ni0.16Cu0.2Zn0.64O)1.02(Fe2O3)0.98铁氧体材料,研究了Bi2O3-V2O5复合添加对材料烧结特性和磁性能的影响.结果表明,复合添加bi2O3-V2O5能促进样品致密化、提高起始磁导率和品质因数.当添加0.3wt%Bi2O3、0.15wt%V2O5时,930℃烧结起始磁导率μi＞800、品质因数(94)、密度(5.12 g/cm3)都达到较大值,比同样配方只掺杂Bi2O3的NiCuZn材料明显提高.     

Synthesis and characterization of novel Ca2Zn4Ti15O36 microwave ceramics derived from sol-gel powder

A novel microwave dielectric ceramics with composition of Ca₂Zn₄Ti₁₅O₃₆ (CZT) have been synthesized at different sintering temperatures, using citrate sol-gel derived powder. The sintering behavior and the phase identification of the powders were evaluated using differential thermal analysis-thermo gravimetric analysis and X-ray powder diffraction analysis techniques. The phase of CZT can be observed in the powder calcined at 900 °C. The single-phase of CZT, however, can only be obtained at sintering temperature of 1,000 °C or above. The single-phase CZT ceramics can be sintered into dense at 1,100 °C, exhibiting excellent microwave dielectric properties of ? _r?=?48.1, Q?×?f?=?27,000 GHz, and τ _f?=?+53.5 ppm/°C. The effects of sintering temperature on the density, microstructure, and dielectric properties of the sintered ceramics were investigated. The mechanism responsible for the change of dielectric properties with sintering temperature was also discussed.     

Low temperature sintering and microwave dielectric properties of Ba3Ti5Nb6O28 with B2O3 and CuO additions

The low sintering temperature and the good dielectric properties such as high dielectric constant (ε _r ), high quality factor (Q × f), and small temperature coefficient of resonant frequency (TCF) are required for the application of chip passive components in wireless communication low temperature co-fired ceramics (LTCC). In the present study, the sintering behaviors and dielectric properties of Ba₃Ti₅Nb₆O₂₈ ceramics were investigated as a function of B₂O₃-CuO content. The pure Ba₃Ti₅Nb₆O₂₈ system showed a high sintering temperature (1250^∘C) and had the good microwave dielectric properties: Q × f of 10,600 GHz, ε _r of 37, TCF of −12 ppm/^∘C. The addition of B₂O₃-CuO was revealed to lower the sintering temperature of Ba₃Ti₅Nb₆O₂₈, 900^∘C and to enhance the microwave dielectric properties: Q × f of 32,500 GHz, ε _r of 40, TCF of 9 ppm/^∘C. From the X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) studies, these phenomena were explained in terms of the reduction of oxygen vacancies and the formation of secondary phases having the good microwave dielectric properties.     

Improved giant dielectric properties in microwave flash combustion derived and microwave sintered CaCu 3 Ti 4 O 12 ceramics

The nanocrystals of CaCu3Ti4O12 ceramic were prepared by microwave flash combustion technique. The microwave sintering of powders was optimized to 1025 − 1075 °C for 20 min with heating and cooling rate of 50 °C/min. Microstructural evaluation of sintered sample was carried out using SEM. The dielectric properties were measured in the frequency range 10–2 × 106 Hz and the temperature range 30–100 °C. The CCTO sample sintered at 1075 °C had giant dielectric constant 53,300 at 100 Hz. It was observed that dielectric constant was greatly increased on a slight increase in sintering temperature. Modulus and impedance analysis were performed to explore the observed unusual dielectric response. Grain and grain boundary resistance were observed as 8 Ω and 350,000 Ω, respectively. The grain boundary activation energy for electro-conduction was calculated as 0.65 eV by using the characteristic frequencies in cole-cole plots. It was noticed that the thermally activated charge carriers had long-range mobility.