Magneto-optical properties of transition metal compounds XPt3 (X = V, Cr, Mn, Fe, Co) and X3Pt (X = Fe, Co)

We have studied theoretically the electronic structure and magneto-optical Kerr effect (MOKE) of XPt₃ (X = V, Cr, Mn, Fe, Co) and X₃Pt (X = Fe, Co) compounds from first principles using the full potential linearized augmented plane wave (FPLAPW) method within the local spin density approximation. The calculated magneto-optical spectra show the features of the experimental spectra which can be attributed to electronic transitions. For the Pt based compounds of 3d transition metals, we find the largest Kerr angle of −1.17° for MnPt₃ in the polar geometry which is in good agreement with the experimental data. Our calculations show an increase in Kerr rotation for XPt₃ series which can be correlated to an increase in the unpaired valence d-electrons of 3d transition metal (X) up to MnPt₃ and then a decrease for FePt₃ and CoPt₃. The Kerr spectrum is analyzed to ascertain the origin of the various peaks in terms of optical transitions. In addition, the effect of interchanging X and Pt atoms in XPt₃ is also studied in order to have greater insight for the dependence of Kerr spectra on configuration and local environment of these two atoms.     

Microstructure and strength of B2-ordered (Ni,Co)Al

A transmission electron microscopy (TEM) investigation of the morphologies and crystal structures of precipitates in supersaturated B2-ordered (Ni,Co)Al has revealed that rod-like precipitates of the (Ni,Co)₂Al phase with a hexagonal structure form parallel to the <111> direction of the B2 matrix. By aging at temperatures below 973 K, a long period superlattice structure of hexagonal (Ni,Co)₂Al was formed. The (Ni,Co)Al hardens appreciably by the precipitation of these phases. An energy dispersive spectroscopy (EDS) was used to analyze the compositions of each phase formed in the B2-(Ni,Co)Al. The effects of the dispersion of the (Ni,Co)₂Al phase on the temperature dependence of the strength of the B2-(Ni,Co)Al have been investigated over a temperature range from 298 K to 1173 K.     

Li(Mn1/3Ni1/3Co1/3)1-yMyO2(M=Al,Mg,Ti)正极材料的制备及性能

采用液相共沉淀合成锰镍钴氢氧化物前驱体, 在前驱体中掺入元素M(M=Al, Mg, Ti), 与锂结合生成Li(Mn1/3Ni1/3Co1/3)0.98M0.02O2材料, 结果表明掺杂可有效提高材料的循环性能. X射线衍射结果表明 随掺钛量增大(0≤y≤0.15), 晶格畸变增大, 半高宽变大, 晶粒粒径增大; 其中掺钛量y=0.1的材料电化学性能表现最好, 以20 mA/g电流充放电, 在2.5～4.6 V电压区首次放电容量可达215 mA·h/g.     

Structure and electrochemical properties of Li(Ni_(0.5)Mn_(0.5))_(1-x)TixO_2 prepared by one-step solid state reaction

1Introduction Many efforts have been made to develop new materials as an alternative to LiCoO2due to the relatively high cost and toxicity of Co.Since OHZUKU and MAKIMURA[1]successfully synthesized LiNi0.5Mn0.5-O2with excellent performance by solid state …     

Cycle stabilities of the La0.7Mg0.3Ni2.55−xCo0.45Mx (M = Fe, Mn, Al; x = 0, 0.1) electrode alloys prepared by casting and rapid quenching

In order to improve the cycle stability of La–Mg–Ni system (PuNi₃-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Fe, Mn and Al, and the electrode alloys La_0.7Mg_0.3Ni_2.55−xCo_0.45M_x (M = Fe, Mn, Al; x = 0, 0.1) were prepared by casting and rapid quenching. The effects of the substitution of Fe, Mn and Al for Ni and rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM indicate that element substitution has no influence on the phase compositions of the alloys, but it changes the phase abundances of the alloys. Particularly, the substitution of Al and Mn obviously raises the amount of the LaNi₂ phase. The substitution of Al and Fe leads to a significant refinement of the as-quenched alloy's grains. The substitution of Al strongly restrains the formation of an amorphous in the as-quenched alloy, but the substitution of Fe is quite helpful for the formation of an amorphous phase. The effects of the substitution of Fe, Mn and Al on the cycle stabilities of the as-cast and quenched alloys are different. The positive influence of the substitution elements on the cycle stabilities of the as-cast alloys is in proper order Al > Fe > Mn, and for as-quenched alloys, the order is Fe > Al > Mn. Rapid quenching engenders an inappreciable influence on the phase composition, but it markedly enhances the cycle stabilities of the alloys.     

Raman active phonons of RFe3(BO3)4, R=La or Nd, single crystals

Oriented single crystals of RFe₃(BO₃)₄, with R=La or Nd, have been studied by Raman spectroscopy. Spectra with the relevant polarization configurations have been recorded in order to obtain the symmetry of the observed phonons. The factor group analysis and the correlation with the free (BO₃)³⁻ ion are done in order to identify most of the phonons associated with the two different types of (BO₃)³⁻ ion present in the crystal. The number and symmetries of the optical Raman active modes are 7A₁+19E, among which 4A₁+8E can be assigned as mostly due to (BO₃)³⁻ vibrations. 7A₁+18E modes were observed.

The highest energy peaks have been assigned to the regular planar (BO₃)³⁻ and to the three irregular (BO₃)³⁻ groups. The two lowest energy peaks of A₁ symmetry (around 180 and 300 cm⁻¹) are very probably related to the BO₃ rotatory mode and to Fe displacements. R ions do not participate in A₁ symmetry modes. The E mode around 90 cm⁻¹ (the lowest frequency mode) is probably due to the R ions which have the longest bonds and are the heaviest ions.     

新型复合贮氢合金Zr_(0.9)Ti_(0.1)(Ni,Co,Mn,V)_(2.1)的制备与电化学性能

采用熔铸方法制备母合金Zr0 .9Ti0 .1(Ni,Co ,Mn ,V) 2 .1,进而在母合金基础上添加吸氢剂B ,利用球磨制得 4种复合贮氢合金。X射线衍射结果表明 ,随着球磨时间的增加 ,复合合金由晶态转化为非晶态 ;电化学测试结果表明 ,复合合金经过 1～ 2次球磨就能完全活化 ,具有很好的活化性能 ;在 6 0mA/g电流下 ,复合贮氢合金C和D的稳定容量均可达到 44 0mA·h/ g左右 ,比母合金高出 80mA·h/ g ;但随着球磨时间的延长 ,所得的复合合金容量比铸态母合金的还低 ;在 30 0mA/g电流下 ,复合合金D具有较好的循环稳定性 ,经过 2 0 0次循环后其容量仅衰减 3 %。     

Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets

When sintered Sm(Co, Fe, Cu, Zr)_z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr)_z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr)_z magnets can keep excellent magnetic properties when the carbon content is below 0.1 wt.%: Br ≥ 10 kGs, H_cj ≥ 22 kOe, BH_max ≥ 25 MGOe. When the carbon content is above 0.1 wt.%, Br, H_cj and BH_max decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)₅ phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43 wt.%, there is not enough Sm(Co, Cu)₅ phase to form a uniform cellular microstructure. Br, H_cj and BH_max are approximate to zero. Since carbon has little influence on the content of Sm₂(Co, Fe)₁₇ phase, Ms can keep a high value (≥100 emu/g). ZrC has high melting point (3420 °C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases.     

Composition dependence of structure and optical properties of Cu2ZnSn(S,Se)4 solid solutions: An experimental study

The evolution of structure and optical properties of Cu₂ZnSn (S_xSe_1−x)₄ (CZTSSe) solid solutions in a wide composition range (0 ≤ x ≤ 1) has not been fully elucidated. We have performed comprehensive characterization on the CZTSSe powders with different S/Se ratios, which were synthesized by the solid state reaction method. X-ray diffraction patterns demonstrate that the lattice parameters a and c of CZTSSe decrease lineally when S replace Se gradually, which obeys the Vegard's rule. The A₁ Raman modes of CZTSSe show a typical two-mode behavior. The absorption spectra reveal that the band gap of CZTSSe can be tuned monotonously between 0.96 and 1.5 eV with almost linearity, and a small band gap bowing constant (b ≈ 0.08 eV) is deduced.     

Synthesis and characterization of layered Li（Ni1/3Mn1/3CO1/3）O2 cathode materials by spray-drying method

Spherical Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 was prepared via the homogenous precursors produced by solution spray-drying method. The precursors were sintered at different temperatures between 600 and 1 000 ℃ for 10 h. The impacts of different sintering temperatures on the structure and electrochemical performances of Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 were compared by means of X-ray diffractometry(XRD), scanning electron microscopy(SEM), and charge/discharge test as cathode materials for lithium ion batteries. The experimental results show that the spherical morphology of the spray-dried powers maintains during the subsequent heat treatment and the specific capacity increases with rising sintering temperature. When the sintering temperature rises up to 900 ℃ , Li(Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 attains a reversible capacity of 153 mA·h/g between 3.00 and 4.35 V at 0.2C rate with excellent cyclability.     

95W-5（Ni／Fe／Co）合金高温变形及影响因素

通过温度、应变速率对95W-5（Ni／Fe／Co）合金流变应力曲线的影响，分析了该合金的变形特点。结果表明：该合金在200℃～600℃温度范围内变形时，初始加工硬化十分显著。宏观上表现为合金的屈服强度较高。95W-5（Ni／Fe／Co）合金在700℃～1300℃的流变应力曲线有一明显的特点就是曲线的斜率变小，而且出现短暂稳定态的流动。这是由于粘结相发牛动态回复的结果。此外该合金的高温塑性亦随应变速率的增大而增加。扫描电镜分析结果从微观上验证了该合金高温塑性变化的原因。     

Structure and electrochemical properties of Li(Ni0.5Mn0.5)1-xTixO2 prepared by one-step solid state reaction

The layered compound Li(Ni_0.5Mn_0.5)_1-xTi_xO₂ powders were prepared with Ni(OH)₂, MnCO₃, Li₂CO₃ and TiO₂ by one-step solid state reaction. The effect of doping Ti on the structure and electrochemical properties was studied. The XRD results indicate that the powders with 0≤x≤0.05 have good layered structure and trace of impurity appears in the samples with x≥0.1. The SEM photographs show that the particle size distributes homogeneously and the sample with x=0.15 has larger particle size than other samples. The charge-discharge tests show that Li(Ni_0.5Mn_0.5)_0.95Ti_0.05O₂ synthesized at 800 °C for 36 h exhibits good electrochemical properties. It firstly delivers 173 mA·h/g and maintains 90% of the initial discharge capacity after 30 cycles. The cyclic voltammetry and differential capacity vs voltage curves show that the major oxidation and reduction peaks are around 3.95 V and 3.75 V, respectively, assigned to Ni²⁺/Ni⁴⁺ oxidation-reduction process. A weak peak around 4.5 V is found during the oxidation process in the first cycle, which can be regarded as the main reason of the large drop of discharge capacity in the initial cycle.     

Formation and chemical leaching effects of nonequilibrium Al0.6(Fe25Cu75) alloy powder produced by rod milling

The formation and chemical leaching effects of a nonequilibrium Al_0.6(Fe₂₅Cu₇₅)_0.4 powder produced by rod milling is described. X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and vibrating sample magnetometry were used to characterize both the as-milled and leached specimens. After 400 h of milling, only the bcc AlFe phase with an amorphous phase was detected in the XRD patterns. The crystallite size for the bcc AlFe phase (110) after 400 h of milling was about 5.3 nm. The peak temperature and the crystallization temperature of the as-milled powders were 448.7 and 428.0 °C, respectively. Al atoms leaching from the as-milled bcc AlFe powders in the L1 condition did not alter the diffraction pattern significantly, even though Al atoms had been removed. After the L1 specimen was annealed at 500 °C for 1 h, the bcc AlFe phase transformed to the fcc Cu, Fe, and CuFe₂O₄ phases. The peak widths of L1 and L2 specimens were similar, but became broader than that of the as-milled powder. The saturation magnetization decreased with increasing milling time, and a value of 10.4 emu/g was reached after 400 h of milling. After cooling the specimen from 750 °C, the magnetization slowly increased at approximately 491.4 °C, indicating that the bcc AlFe phase had transformed to the fcc Cu and Fe phases.     

Microstructure and electromagnetic properties of Al18B4O33w/Co composite particles prepared by electroless plating method

Al₁₈B₄O₃₃w/Co composite particles were prepared successfully through electroless plating Co on Al₁₈B₄O₃₃ whiskers. The growth behavior of the coatings, the effect of the process parameters and the electromagnetic properties of the prepared Al₁₈B₄O₃₃w/Co composite particles were investigated. The reduced Co nucleated first on the pre-activated surface of the whiskers to form insular particles which then grew larger gradually and eventually merged together to form continuous coatings. The reaction rate increased but the mass gain decreased with the increase of the bath pH and the bath temperature. The crystallinity of the deposited Co decreased with the increase of phosphorous content as well as the bath temperature. The effect of loading is much weaker compare to that of bath pH and bath temperature. The permittivity and the permeability of the prepared Al₁₈B₄O₃₃w/Co composite particles are markedly higher than those of the raw Al₁₈B₄O₃₃ whiskers in microwave band. Relaxation resonance is found in the samples with thick Co coatings due to the presence of eddy current, which deteriorates the permeability of the Al₁₈B₄O₃₃w/Co composite particles.     

Influences of the substitution of Fe for Ni on structures and electrochemical performances of the as-cast and quenched La0.7Mg0.3Co0.45Ni2.55−xFex (x = 0–0.4) electrode alloys

In order to improve the cycle stability of the La–Mg–Ni system PuNi₃-type hydrogen storage electrode alloys, Ni in the alloy was partially substituted by Fe. The La_0.7Mg_0.3Co_0.45Ni_2.55−xFe_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substitution of Fe for Ni on the structures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results of the electrochemical measurement indicate that the substitution of Fe for Ni obviously decreases the discharge capacity, high rate discharge capability (HRD) and discharge potential of the as-cast and quenched alloys, but it significantly improves their cycle stabilities, and its positive impact on the cycle life of as-quenched alloy is much more significant than on that of the as-cast one. The microstructure of the alloys analyzed by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two major phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Fe for Ni helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously increase.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Microstructure and shape-memory characteristics of Ni56Mn25−xCoxGa19 (x = 4, 8) high-temperature shape-memory alloys

NiMnCoGa alloys were studied as candidate of high-temperature shape-memory alloys with Mn substituted by Co. The results show that the hot workability and room-temperature ductility of NiMnGa alloys can be greatly improved by forming ductile γ phase through Co addition. When the amount of γ phase is about 19%, the tensile stress and strain are 491 MPa and 8.2%, respectively. When the amount of γ phase increased to about 43%, the tensile stress and strain are 729.3 MPa and 14.1%, respectively. The reversible strain due to shape-memory effect is 2.1% under a prestrain of 5.3% for x = 4, and the shape-memory ability almost disappears for x = 8 due to large amount of γ phase, which seriously hampers the reorientation of martensitic variants and/or detwinning.     

93W/Ni/QSn4-3扩散焊接接头的显微结构和力学性能

采用扩散焊接的方法制备出加入Ni箔中间层的钨合金(93w)与锡青铜合金(QSn4-3)焊接接头样品.利用XRD,SEM和EPMA对焊接接头的物相组成和显微结构进行了分析,并测量了焊接接头样品的抗拉强度.结果表明,加镍的93W与QSn4-3进行扩散焊接时,焊接层的显微结构结合紧密,Ni与Cu元素之间以及93W合金的添加剂元素在Ni箔中分布存在明显的连续变化层.物相分析和显微硬度结果表明Ni元素与QSn4-3中的Cu元素和93W的添加剂元素的固溶反应,促进了93W,Ni/QSn4-3焊接接头强度的大幅度提高.

Abstract：

The 93W/Ni/QSn4-3 joint was prepared by diffusion bonding at vacuum using pure nickel foil as interface layer. The microstructure and composition were characterized by SEM and EP-MA. The tensile strength of joint was also measured. The test results show that Ni foil improves the tensile strength of 93W/Ni/QSn4-3 joint. The thickness of Ni interlayer becomes thiner obviously because of the diffusion layer between Ni element of Ni foil and W and additional elements of 93W alloy, as well as the gradient layer of Ni and Cu elements. Solution reactions between Ni element of Ni foil and Cu element of QSn4-3 alloy, W and additional elements of 93W alloy achieve the joint of 93W/Ni/QSn4-3, that is why tensile strength of 93W/Ni/QSn4-3 joint welded is improved.