Electric and dielectric properties of MgGd0.1Fe1.9O4 ferrite

MgGd_0.1Fe_1.9O₄ ferrite with improved electrical and dielectric properties has been synthesized by conventional ceramic technique. X-ray analysis confirmed the single-phase inverse spinel structure of the ferrite. The dc resistivity is increased by one order of magnitude as compared to Magnesium ferrite. The dielectric loss of the sample investigated at room temperature is only 3 × 10⁻³ at 3 MHz. High resistivity and low dielectric loss can be correlated with better compositional stoichiometry, size and nature of the additives. The variation of dielectric properties of the sample as a function of frequency in the range 0.1–20 MHz has been studied at different temperatures. In addition to this, the electric and dielectric properties have been studied as a function of temperature. Possible mechanisms contributing to the results have been discussed minutely in this paper.     

AlN ceramics prepared by high-pressure sintering with La2O3 as a sintering aid

The magnetic and dielectric properties of Bi–Zn codoped Y-type hexagonal ferrite was investigated. The samples with composition of Ba_2−xBi_xZn_0.8+xCo_0.8Cu_0.4Fe_12−xO₂₂ (x = 0–0.4) were prepared by the solid-state reaction method. Phase formation was characterized by X-ray diffraction. The microstructure was observed via scanning electron microscopy. The magnetic and dielectric properties were measured using an impedance analyzer. Direct current (dc) electrical resistivity was measured using a pA meter/dc voltage source. Minor Bi doping (x = 0.05–0.25) will not destroy the phase formation of Y-type hexagonal ferrite, but lower the phase formation temperature distinctly. Bi substitution can also promote the sintering process. The Bi-containing samples (x > 0.05) can be sintered well under 900 °C without any other addition. The sintering temperature is about 200 °C lower than that of the Bi-free sample. The Bi–Zn codoped samples exhibit excellent magnetic and dielectric properties in hyper frequency. These materials are suitable for multi-layer chip-inductive components.     

Impedance spectroscopy and dielectric properties of Ce and La substituted Pb0.7Sr0.3(Fe0.012Ti0.988)O3 nanoparticles

We present the structural, microstructural, dielectric and impedance behavior of Pb_0.7Sr_0.3[(Fe_2/3Ce_1/3)_0.012Ti_0.988]O₃ (PSFCT) and Pb_0.7Sr_0.3[(Fe_2/3La_1/3)_0.012Ti_0.988]O₃ (PSFLT) nanoparticles. These nanoparticles were prepared by a chemical synthesis route using polyvinyl alcohol as surfactant. The X-ray diffraction pattern shows polycrystalline nature with coexistence of tetragonal and cubic phase in both PSFCT and PSFLT nanoparticles. The average particle size has been measured using Scherer's relation. The average particle sizes also measured by TEM are 10 and 11 nm, and by SEM 9 and 12 nm, respectively, of PSFCT and PSFLT nanoparticles. By measuring the value of relative permittivity (?′) and loss (tan δ) at lower frequency, the dielectric properties show Maxwell-Wagner type interfacial polarization. However, due to nano size effect of PSFCT and PSFLT, dispersionless dielectric response has been observed up to higher frequency of 15 MHz. The frequency dependent real (Z′) and imaginary (Z″) parts of impedance confirmed the variation which was observed in dielectric properties. The values of resistance of grain boundaries, R_gb is higher than grains, R_g indicates that the effect of grain boundaries is dominant on electrical properties when the size of nanoparticles is quite small.     

Microwave dielectric properties of temperature stable Li2ZnxCo1−xTi3O8 ceramics

The Li₂Zn_xCo_1−xTi₃O₈ (x = 0.2-0.8) solid solution system has been synthesized by the conventional solid-state ceramic route and the effect of Zn substitution for Co on microwave dielectric properties of Li₂CoTi₃O₈ ceramics has also been investigated. The microwave dielectric properties of these ceramics show a linear variation between the end members for all compositions. The optimized sintering temperatures of Li₂Zn_xCo_1−xTi₃O₈ ceramics increase with increasing content of Zn. The specimen with x = 0.4 sintered at 1050 °C/2 h exhibits an excellent combination of microwave dielectric properties with ?_r = 27.7, Q_u × f = 57,100 GHz and τ_f = −1.0 ppm/°C.     

Preparation of textured K2BiNb5O15 ceramics with rod-like templates by the screen-printing technique

This work focuses on the fabrication of textured ceramics with rod-like templates using screen-printing technique. Rod-like K₂BiNb₅O₁₅ (KBIN) crystals with an aspect ratio of 10:1 were synthesized by the reaction of K₂CO₃, Bi₂O₃ and Nb₂O₅ in molten KCl flux at 1100 °C for 2 h. The KBIN templates were mixed with equiaxed powder of the same composition and oriented through the screen-printing reactive templated grain growth (SP-RTGG) technique. By printing onto a flexible polymer substrate and repeating the process of printing and drying, thick films with a thickness of several hundred micrometers were produced, then subsequently removed from the substrate, stacked layer by layer together and pressed into pieces. Textured KBIN ceramics were successfully obtained by this method. SEM and XRD were performed to study the grain growth and orientation degree. The textured K₂BiNb₅O₁₅ ceramics showed an orientation degree (Lotgering factor) of 42% along 〈0 0 1〉 direction. The analysis of the dielectric properties of the textured K₂BiNb₅O₁₅ ceramics revealed obvious anisotropies.     

Synthesis and characterization of polypropiolate sodium (PPNa)-Fe3O4 nanocomposite

Polypropiolate sodium (PPNa)-Fe₃O₄ nanocomposites were successfully synthesized by the precipitation of Fe₃O₄ in the presence of sodium polypropiolate and followed by reflux route. Structural, morphological, electrical and magnetic properties evaluation of the nanocomposite were performed by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating scanning magnetometry (VSM) and conductivity measurements. Crystalline phase was identified as magnetite with an average crystallite size of 7 ± 3 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM, by log-normal fitting, is ∼9 ± 1 nm. FT-IR analysis shows that the binding of PPNa on the surface of iron oxide is through bidentate linkage of carboxyl group. TGA analysis showed the presence of 20% PPNa around 80% magnetic core (Fe₃O₄)…PPNa-Fe₃O₄ nanocomposite show superparamagnetic characteristics at room temperature. It is found that the a.c. conductivity of the nanocomposites obeys the well-known power law of frequency in which it also depends on temperature. Additionally, its d.c. conductivity showed that two operating regions of the activation energy. Both real and imaginary parts of either permittivity exhibit almost the same attitudes which are the indication of the same ability in the stored energy, and dissipation of energy within the PPNa and PPNa-Fe₃O₄ nanocomposites.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Impedance analysis of thermally modified SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)₂O₉ (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. The obtained samples were thermally modified in high vacuum to study the influence of the formed defects on the dielectric and electrical properties of the samples. Scanning electron microscopy with an energy dispersion X-ray spectrometer was applied to investigate the grain structure and stoichiometry of the studied ceramics. Their dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material which was controlled by thermal modification of the tested ceramics. This phenomenon can be ascribed to the presence of ionized space charge carriers such as oxygen and bismuth vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. Moreover the temperature dependence of various electrical properties was determined and discussed.     

通过水热法合成的纳米铁酸镍/石墨复合阳极材料具有优异的电化学性能

作为锂离子电池阳极材料的铁酸镍及其相关材料,由于其具有较高的理论比容量,近来受到广泛关注。为了克服在充放电过程中的较低导电性与较大的体积膨胀等不良因素,本文通过水热法合成了纳米铁酸镍钉扎在石墨表面而形成的复合物。该纳米铁酸镍/石墨复合物表现出了较高的比容量以及优异的循环性能。其初始放电容量接近1478mAh g-1,并且在100 mA g-1的电流密度下循环50周之后,其可逆容量依然高达1109 mAh g-1。在1000 mA g-1的充电电流情况下,该复合材料的充电容量也能保持750 mA g-1。这优异的电化学性能主要归功于纳米铁酸镍能够稳定的钉扎在石墨表面上,这种特殊的结构增强了材料的导电性同时也增大了材料的表面比容量。     

Growth and dielectric properties of Ca3NbGa3Si2O14 crystals

A new langasite type single crystal Ca₃NbGa₃Si₂O₁₄ (CNGS) was grown by Czochralski (CZ) method. The structure of CNGS crystal was determined by X-ray powder diffraction, the lattice parameters were a=0.8087 ± 0.0001 nm, c=0.4974 ± 0.0002 nm, V=0.2817 ± 0.0002 nm³; The congruency of CNGS was examined by measuring the chemical composition of the grown crystal by quantitative X-ray fluorescent (XRF) analysis. The melting point of CNGS crystal was measured by using the differential scanning calorimetry (DSC). Dielectric properties of (1 1 0) wafer plate were studied in the temperature range from 298.15 to 873.15 K; the frequency dependence of dielectric loss in the frequency range 10 Hz–13 MHz was measured.     

Effect of Ni substitution on the structural and transport properties of NixMn0.8−xMg0.2Fe2O4; 0.0 ≤ x ≤ 0.40 ferrite

Ni_xMn_0.8−xMg_0.2Fe₂O₄; 0.0≤ x ≤0.40 was prepared by standard ceramic technique, presintering was carried out at 900 °C and final sintering at 1200 °C with heating/cooling rate 4 °C/min. X-ray diffraction analyses assured the formation of the samples in a single phase spinel cubic structure. The calculated crystal size was obtained in the range of 75-130 nm. A slight increase in the theoretical density and decrease in the porosity was obtained with increasing the nickel content. This result was discussed based on the difference in the atomic masses between Ni (58.71) and Mn (54.938). IR spectral analyses show four bands of the spinel ferrite for all the samples. The conductivity and dielectric loss factor give nearly continuous decrease with increasing Ni-content. This was discussed as the result of the significant role of the multivalent cations, such as iron, nickel, manganese, in the conduction mechanism. Anomalous behavior was obtained for the sample with x = 0.20 as highest dielectric constant, highest dielectric loss and highest conductivity. This anomalous behavior was explained due to the existence of two divalent cations on B-sites with the same ratio, namely, Mg²⁺ and Ni²⁺.     

Low-firable high-K dielectric in the Zrx(Zn1/3Nb2/3)1−xTiO4 ceramic system

Composite ceramics in the solid solution of Zr_x(Zn_1/3Nb_2/3)_1−xTiO₄ (x = 0.1-0.4) have been prepared by the mixed oxide route. Formation of solid solution was confirmed by the X-ray diffraction patterns. The microwave dielectric properties, such as dielectric constant (?_r), Q × f value and temperature coefficient of resonant frequency (τ_f) have been investigated as a function of composition and sintering temperature. With x increasing from 0.1 to 0.4, the dielectric constant decreases from 70.9 to 43.2, and the τ_f decreases from 105 to 55 ppm/°C. The Q × f value, however, increases with increasing x value to a maximum 26,600 GHz (at 6 GHz) at x = 0.3, and then decreases thereafter. For low-loss microwave applications, a new microwave dielectric material Zr_0.3(Zn_1/3Nb_2/3)_0.7TiO₄, possessing a fine combination of microwave dielectric properties with a high ?_r of 51, a high Q × f of 26,600 GHz (at 6 GHz) and a τ_f of 70 ppm/°C, is suggested.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

(Y_(0.95)Eu_(0.05))_2O_3亚微米球、微米板片的选择合成及荧光性能的形貌依存性(英文)

采用先水热合成(150°C,12h)、后煅烧(1000°C)来实现(Y0.95Eu0.05)2O3亚微米球形和微米板片红色荧光颗粒的形貌可控合成。通过XRD、FT-IR、FE-SEM和PL等检测手段对样品进行分析。结果表明:将尿素与Y+Eu的摩尔比由10增大至40～100,得到的前驱体由碱式碳酸盐亚微米球转变为碳酸盐微米片;经1000°C煅烧所得氧化物能够继承前驱体的形貌特征;板片二维形貌的限制内部晶粒自由生长,使更多的(400)晶面暴露在板片颗粒表面;在250nm紫外光的激发下,荧光颗粒的荧光发射峰位及荧光不对称因子[I(5D0→7F2)/I(5D0→7F1),～11]均与颗粒形貌的相关性不强,但荧光强度呈现明显的形貌依存性;微米板片颗粒的尺寸大,从而其比表面积小,因此具有更高的荧光强度(微米板片在～613nm处的荧光强度为球形颗粒的～1.33倍)。     

Microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric resonators

Ba(Zn_1/3Ta_2/3)O₃ (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO₃, ZnO, and Ta₂O₅ powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications.     

Structural and electrochemical properties of LiV3O8 prepared by combustion synthesis

LiV₃O₈ powders were prepared by combustion synthesis, using metallic nitrates as the oxidant and metal sources and urea as fuel. The effect of (Li + V)/CO(NH₂)₂ ratio and heat-treatment temperature on the structure and electrochemical properties were discussed. The electrochemical behavior of the product showed that sample B₁ synthesized at 300 °C with 1:0.5 ratio of (Li + V)/CO(NH₂)₂ showed the highest initial discharge capacity of 317.3 mAh g⁻¹ and the best cycle ability with 238.9 mAh g⁻¹ after 30 cycles.     

Preparation of Fe2O3/graphene composite and its electrochemical performance as an anode material for lithium ion batteries

The micro-sized sphere Fe₂O₃ particles doped with graphene nanosheets were prepared by a facile hydrothermal method. The obtained Fe₂O₃/graphene composite as the anode material for lithium ion batteries showed a high discharge capacity of 660 mAh g⁻¹ during up to 100 cycles at the current density of 160 mA g⁻¹ and good rate capability. The excellent electrochemical performance of the composite can be attributed to that graphene served as dispersing medium to prevent Fe₂O₃ microparticles from agglomeration and provide an excellent electronic conduction pathway.     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.     

Spectroscopic and dielectric studies on MnO doped PbO–Nb2O5–P2O5 glass system

PbO–Nb₂O₅–P₂O₅ glasses containing different concentrations of MnO ranging from 0 to 2.5 mol% were prepared. A number of studies viz., differential thermal analysis, infrared, optical absorption, luminescence, Raman and ESR spectra, magnetic susceptibility and dielectric properties (constant ′, loss tan δ, ac conductivity σ_ac over a range of frequency and temperature) of these glasses have been carried out. The results have been analyzed in the light of different oxidation states of manganese ions. The analysis indicates that when the concentration of MnO is around 1.0 mol%, manganese ions mostly exist in Mn²⁺ state, occupy network forming positions with MnO₄ structural units and increase the rigidity of the glass network. When MnO is present in higher concentrations, these ions seem to exist mostly in Mn³⁺ state and occupy modifying positions.     

Nb2O5掺杂NiFe2O4陶瓷材料的显微结构和导电性能

以NiO、Fe2O3和Nb2O5为原料,采用固相烧结法合成陶瓷粉体,通过等静压-气氛烧结法制备Ni1-xNbxFe2O4(x=0,0.02,0.05,0.07,0.10,0.20)陶瓷试样,并对其进行导电性能测试。通过XRD、SEM、EDX、FTIR和XPS等分析手段对材料的物相组成、显微结构和微区成分进行表征,研究Nb2O5掺杂对陶瓷材料显微结构和导电性能的影响。结果表明:Nb2O5掺杂抑制NiFe2O4基体中NiO相的出现,过量时生成FeNbO4相;适量掺杂(x=0.05)有利于消除晶界孔隙,提高陶瓷的烧结密度;与未掺杂试样相比,掺杂Nb2O5的NiF2O4陶瓷材料的导电性均得到很大改善,其中掺杂量x=0.05的Ni0.95Nb0.05Fe2O4陶瓷试样在1 233 K的电导率较纯NiFe2O4的提高60%。