Solid-phase epitaxy of CaSi2 on Si(1 1 1) and the Schottky-barrier height of CaSi2/Si(1 1 1)

Thin Ca films were evaporated on Si(1 1 1) under UHV conditions and subsequently annealed in the temperature range 200–650 °C. The interdiffusion of Ca and Si was examined by ex situ Auger depth profiling. In situ monitoring of the Si 2p core-level shift by X-ray photoemission spectroscopy (XPS) was employed to study the silicide formation process. The formation temperature of CaSi₂ films on Si(1 1 1) was found to be about 350 °C. Epitaxial growth takes place at T≥400 °C. The morphology of the films, measured by atomic force microscopy (AFM), was correlated with their crystallinity as analyzed by X-ray diffraction (XRD). According to measurements of temperature-dependent I–V characteristics and internal photoemission the Schottky-barrier height of CaSi₂ on Si(1 1 1) amounts to qΦ_Bn=0.25 eV on n-type and to qΦ_Bp=0.82 eV on p-type silicon.     

On a new calcium vanadate: synthesis, structure and Li insertion behavior

A synthetic form of the mineral hewettite was prepared via a new route in aqueous medium, starting either from the crystalline compound Li_1.1V₃O₈, or from its amorphous precursor. The anhydrous, crystalline derivative Ca_0.5V₃O₈ was obtained by heating the synthetic hewettite at 250°C under dynamic vacuum. The diffraction studies show that the 2D structure of Ca_0.5V₃O₈ involves the same V₃O₈ layers as in the hewettite or in Li_1+αV₃O₈. The stacking of the layers is similar to that in the metahewettite. A structural model is proposed, where the Ca²⁺ ions occupy octahedral sites in the interlayer space. The electrochemical behavior of Ca_0.5V₃O₈ vs. lithium insertion is presented. It is original and reveals particularly good performances in terms of stability during cycling at C/5 rate. The homologues obtained with Mg or Ba, instead of Ca, are briefly presented.     

Microwave absorption properties of composite powders with low density

The composites of barium ferrite coated on hollow ceramic microspheres were prepared using sol-gel technique. The crystal structure, morphology and microwave absorption properties of composite powders with different weight ratio of microspheres were studied with XRD, EDS, FESEM and vector network analyzer. The results show that the microwave absorption properties of composite powders are greatly improved. The maximum microwave loss of composite powders reaches 31 dB with an amount of 50 wt.% microspheres, and its density is only about 1.80 g/cm³. The effect of hollow ceramic microspheres on the microwave absorption property is also discussed.     

Preparation and microwave absorption properties of electroless Co-Ni-P coated strontium ferrite powder

A new type of Co-Ni-P coated strontium ferrite nanocomposite was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The plating process was studied carefully. The morphology, crystal structure and microwave absorption properties of the Co-Ni-P coated powder were studied with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDX) and vector network analyzer. The results show that the strontium ferrite powder was successfully coated with Co-Ni-P alloy and possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −44.12 dB. The bandwidth with the loss above −10 dB exceeds 13.8 GHz.     

VUV-UV excited luminescent properties of LnCa4O(BO3)3:RE (Ln=Y, La, Gd; Re=Eu, Tb, Dy, Ce)

Calcium lanthanide oxyborate doped with rare-earth ions LnCa₄O(BO₃)₃:RE³⁺ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band E_ct were calculated and compared with their excitation spectra.Eu³⁺ and Tb³⁺ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce³⁺ ions do not show efficient luminescence and quench the luminescence of Tb³⁺ ions when Tb³⁺ and Ce³⁺ ions are co-doped into LnCOB. GdCOB doped with Dy³⁺ shows yellowish white light under irradiation of 254 nm light for the reason that Gd³⁺ ions transfer the energy from itself to Dy³⁺. Because of the existence of Gd³⁺, the samples of GdCOB:RE³⁺ show higher excitation efficiency than LaCOB:RE³⁺ and YCOB:RE³⁺, around 188 nm, which indicates that the Gd³⁺ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb³⁺, Dy³⁺ and Eu³⁺.     

光电光谱法分析钢中钙

本文研究了用光电光谱法测定钢中钙的方法 ,确定了最佳分析条件 ,分析了共存元素的干扰情况。用本方法测定钢中钙 ,具有良好的准确度和精密度 ,结果令人满意。     

复合型铁氧体全极化器

应用耦合波理论 ,对有两组NS/N′S′四磁极磁化铁氧体中极化传输进行了分析 .在X、S波段对多种椭圆极化进行了测试 ,还完成了 0°～ 180°范围内多种线极化波测试 .最后对全极化器应用作了简单介绍 .     

Mössbauer study of nanodimensional nickel ferrite – mechanochemical synthesis and catalytic properties

Iron–nickel spinel oxide NiFe₂O₄ nanoparticles have been prepared by the combination of chemical precipitation and subsequent mechanical milling. For comparison, their analogue obtained by thermal synthesis is also studied. Phase composition and structural properties of iron–nickel oxides are investigated by X-ray diffraction and Mössbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. An influence of the preparation method on the reduction and catalytic properties of iron–nickel samples is established.     

Effects of pH and citric acid contents on characteristics of ester-derived BaFe12O19 powder

The single domain size of BaFe₁₂O₁₉ powder with crystallite sizes less than 200 nm was produced using a citric acid precursor method. Fe³⁺ and Ba²⁺, in a molar ratio of 12, were chelated by COOH⁻ in an aqueous solution. After ethylene glycol additions, esterification, dehydration, and calcination led to the formation of ester-derived BaFe₁₂O₁₉ powder. High pH and/or high citric acid contents in the starting solution are required to complete chelate metallic ions in the solution and to form pure barium ferrite powder at 1073 K. Pure single magnetic domain BaFe₁₂O₁₉ particles of M(30 kOe)≈54 emu/g, M_r≈28 emu/g, and H_c≈3.7 kOe were produced using [citric acid]/[metallic ions]=1.5 and pH7.     

Effects of microstructure on the temperature dependence of relative initial permeability of NiCuZn ferrites

In the present work, ferrites with compositions of (Ni_0.27Zn_0.64Cu_x)Fe_1.98O₄ (x=0.1, 0.2) were prepared by conventional ceramic methods. The relationship between the microstructure and the temperature dependence of relative initial permeability was investigated. It was found that intergranular pores in the ferrites generate large demagnetizing fields, reducing the temperature dependence of the effective anisotropy field H_eff, and decreasing the temperature dependence of the relative initial permeability accordingly. However, intragranular pores pin the movement of domain walls. Compared with the permeability induced by domain wall motion, the permeability that resulted from the spin rotation is more sensitive to temperature. As a result, the relative initial permeability of ferrites becomes more sensitive to temperature with increasing micropores within grains.