Preparation and dielectric properties of La doped NBCCTO ceramics

Journal of Electroceramics - CaCu3Ti4O12 ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical...     

Phase transformation and microwave dielectric properties of BiPO4 ceramics

Monazite-type compounds, BiPO₄ polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO₄ has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600^∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950^∘C has good microwave dielectric properties; the relative dielectric constant (ε _r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ _f ) = − 79 ppm/ ^∘C.     

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.     

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.     

Synthesis, characterization and giant dielectric properties of CaCu3Ti4O12 ceramics prepared by a polyvinyl pyrrolidone-dimethylformamide solution route

CaCu₃Ti₄O₁₂ powders were successfully prepared by a polyvinyl pyrrolidone-dimethylformamide solution route. Pure phase of CaCu₃Ti₄O₁₂ was achieved at a low calcination temperature and short reaction time at 800 °C for 3 h. High porosity and neck-grain growth network were observed in CaCu₃Ti₄O₁₂ powders. The sintered CaCu₃Ti₄O₁₂ ceramic with fine-grained microstructure exhibited a very high dielectric constant of 1.26?×?10⁴ and low loss tangent of about 0.07 at 1 kHz and 20 °C. Nonlinear current-voltage behavior and dielectric properties were found to be closely related to the microstructure.     

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.     

Effects of BaWO4 and MnWO4 on the microwave dielectric properties of (Zr0.8 Sn0.2)TiO4 ceramics

Abstract

The effects of BaWO₄ and MnWO₄ on the microwave dielectric properties for (Zr_0.8Sn_0.2)TiO₄ ceramics have been investigated as a function of additives concentrations (0–5 mol%). As the amount of BaWO₄ and MnWO₄ increase up to 1 mol%, the unloaded Q increases due to reduction of the oxygen vacancy concentration. Further addition of BaWO₄ or MnWO₄ causes the unloaded Q to decrease due to the presence of secondary phases, either BaWO₄ itself or a needle shaped undetermined MnWO₄ phase. The temperature coefficient of resonant frequency can be controlled by the volume mixing rule for (Zr_0.8Sn_0.2)TiO₄ and secondary phases.     

Microwave dielectric properties of Mg4Nb2O9 ceramics produced by hydrothermal synthesis

Mg₄Nb₂O₉ ceramics have been prepared by a hydrothermal synthesis in order to reduce the sintering temperature. The sintering and microwave dielectric properties of the hydrothermally processed Mg₄Nb₂O₉ were studied under various sintering temperatures ranging from 900 to 1300°C. The highest Q×f _o value of 26,069 GHz was obtained at the sintering temperature of 1300°C and is attributed to the increased density and appropriate grain growth. τ _f value of ?17.1 ppm/°C was improved by the addition of TiO₂ and τ _f value of 6.7 ppm/°C was obtained at 20 wt% TiO₂. Chemical compatibility of Mg₄Nb₂O₉ with Ag was tested to identity the possibility of using Mg₄Nb₂O₉ for an LTCC application. Since any secondary phase was not observed in the XRD pattern of the mixtures of Mg₄Nb₂O₉ and Ag powder heat treated at 900°C, it was considered that the Mg₄Nb₂O₉ system is applicable to the multilayer microwave devices using Ag as an electrode.     

Stability and microwave dielectric characteristics of (Ca1−x Sr x )LaAlO4 ceramics

The stability of K₂NiF₄ structure in MRAlO₄ (M?=?Sr and Ca; R?=?=?La, Nd, Sm, and Y) ceramics was discussed via calculating the relative difference between the tolerance factors for ABCO₄ and ABO₃ structure, and the K₂NiF₄ structure became unstable when the above difference was greater than 4.3%. Among the above ceramics, CaLaAlO₄ and SrYAlO₄ were not stable. To improve the stability of K₂NiF₄ structure in CaLaAlO₄, the effects of Sr substitution for Ca were investigated. The stability of K₂NiF₄ structure in (Ca_1?x Sr _x )LaAlO₄ ceramics increased with increasing x, and it became stable when x?>?0.9. Good microwave dielectric properties were achieved in (Ca_0.05Sr_0.95)LaAlO₄ ceramics: ??=?16.7, Q.f?=?28,171 GHz, τ _f ?=??52.4 ppm/°C.     

Structural and dielectric properties of BaCexTi1-xO3 ceramics

ABSTRACT

In this paper, we prepare silver nanowires circuit graphics by UV-curing technology. The optimal condition of preparation of the silver nanowires circuit graphics are examined. Experiment results show that the UV-curing technology is a kind of individual, low-cost and environment-friendly method to prepare silver nanowires circuit graphics. The main influence factors on the lines' width are the UV beam power and scanning speed. And we also study the influence of the hot pressing temperature on the resistivity of the circuit graphics. In the experiments, the optimal condition is that the UV beam power is 190 mW and the scanning rate is 6 cm/s, then we get the minimum line width, which is 0.25 mm. The thickness of silver nanowires layer is 100 µm and the hot pressing temperature is 100°C, we will get the sample whose resistivity is 21× 10^?5 Ω·cm.     

Effects of structural characteristics on microwave dielectric properties of (1−x)CaWO4 –xLaNbO4 ceramics

Dependences of microwave dielectric properties on the structural characteristics of (1−x)CaWO₄–xLaNbO₄ ceramics were investigated as a function of LaNbO₄ content (0.0 ≤ x ≤ 0.5). A single phase with tetragonal scheelite structure was obtained up to x = 0.35, and then the mixture phases with scheelite and fergusonite structure were detected. With the increase of LaNbO₄, the deviation of the observed dielectric polarizabilities calculated by the Clausius-Mosotti equation from the theoretical values calculated by the additivity rule of dielectric polarizability, was decreased due to the decrease of oxygen bond valence in ABO₄ scheelite structure. Dielectric constant (K) and temperature coefficient of resonant frequency (TCF) were increased with LaNbO₄ content due to the decrease of oxygen bond valence. Q ⋅ fvalue was dependent on the atomic packing fraction of unit cell as well as the grain size. Typically, K = 13.3, Qf = 50,000 GHz and TCF = −8.7 ppm/^oC were obtained for the specimens with 0.3 mol of LaNbO₄ sintered at 1150^oC for 3 h.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

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.     

K2FeO4的制备、表征及其电化学性能

高产率制备K2FeO4以及考察用其制作碱性Zn/K2FeO4模拟电池的电性能.以KClO、Fe(NO3)3为原料,用氧化法制备K2FeO4,研究了反应温度、反应时间以及KClO与Fe(NO3)3物质的量比等因素对K2FeO4产率的影响;用红外光谱对产物进行了分析表征;还测试了碱性Zn/K2FeO4模拟电池的电性能.研究结果表明:在饱和的KOH体系下控制反应温度为30℃,反应时间为90 min,KClO与Fe(NO3)3的物质的量比为1.5:1.0时制备K2FeO4可得到最佳产率;红外光谱的分析证实,所得产物的主要成分是K2FeO4;碱性Zn/K2FeO4模拟电池的电性能与碱性Zn/MnO2模拟电池的相比,开路电压达1.72 V(后者为1.5 V),平均工作电压1.42 V(后者为1.2 V);放电曲线更平稳,K2FeO4的放电比容量比MnO2的高48.7%.     

Fabrication and characterization of micropatterned barium titanate ceramics

A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO₃) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO₃ nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO₃ nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO₃ nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO₃ ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films.     

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.     

LiNixMn2-xO4材料的合成和性能表征

采用共沉淀法制备了锂离子电池正极材料LiNixMn2-xO4（x=0.1,0.2,0.3,0.4,0.5,0.6）。XRD测试结果表明,除LiNi0.6Mn1.4O4外,其他的试样均为尖晶石结构。电化学性能测试表明：试样在4.0 V左右平台的容量随掺镍量的增加而减小,在4.7 V左右平台的容量随掺镍量的增加而增加,但总容量变化不大。试样的循环性能随掺镍量的增加而提高。     

PVDF-HFP/AgClO4-丙酮固体电解质的制备和性能

制备了PVDF-HFP/AgClO4-丙酮高分子固体电解质,用差示扫描量热法(DSC)、X射线衍射光谱法(XRD)及阻抗测量表征了电解质的性能。该电解质室温电导率达7.32×10-4S/cm,添加乙酰丙酮后,电导率可上升至10-3S/cm。体系在75℃以下稳定,较高温度下由于丙酮等溶剂挥发而使导电性能下降。