Volume collapse phase transitions in cerium-praseodymium alloys under high pressure

Cerium-12at%Praseodymium(Ce_0.88Pr_0.12) and Ce-50at%Praseodymium(Ce_0.50Pr_0.50) alloy samples that contain a random solid-solution of Ce (4f¹ (J?=?5/2)) and Pr (4f² (J?=?4)) localized f-states have been studied by angle dispersive x-ray diffraction in a diamond anvil cell to a pressure of 65?GPa and 150?GPa respectively using a synchrotron source. Ce_0.88Pr_0.12 alloy crystallizes in a face-centered cubic (γ-phase) structure at ambient conditions, while Ce_0.50Pr_0.50 alloy crystallizes in the double hexagonal close packed (dhcp) structure at ambient conditions. Two distinct volume collapse transitions are observed in Ce_0.88Pr_0.12 alloy at 1.5?GPa and 18?GPa with volume change of 8.5% and 3% respectively. In contrast, Ce_0.50Pr_0.50 alloy shows only a single volume collapse of 5.6% at 20?GPa on phase transformation to α-Uranium structure under high pressure. Electrical transport measurements under high pressure show anomalies in electrical resistance at phase transitions for both compositions of this alloy.     

Electron transport properties of ß-phase Co0.50Ti0.50 alloy films with various degrees of long range order

The influence of the structural disorder on the electron transport properties of Co_0.50Ti_0.50 alloy films in a temperature range of 4.2-300 K has been investigated at zero and 0.5 T of magnetic field. The disordered state in the alloy films was obtained by vapor quenching deposition onto substrates cooled by liquid nitrogen. The changes in the transport properties of the alloy films caused by the order-disorder structural transformation and the external magnetic field are explained by the analyses using various models for the electron transport in the disordered systems. Received 18 May 1999 and Received in final form 18 January 2000     

Preparation of a novel Ni/Co-based alloy gradient coating on surface of the crystallizer copper alloy by laser

A high wear-resistant gradient coating made of Ni/Co-based alloys on the surface of a Cu alloy substrate was synthesized using a YAG laser induced in situ reaction method. The coating consists of three layers: the first is a Ni-based alloy layer, the second and third are Co-based alloy layers. The microhardness increases gradually from 98 HV in the Cu alloy substrate to the highest level of 876 HV in the third layer. The main phase of the Co-based alloy layer is CoCr₂(Ni,O)₄, coexisting with the Fe₁₃Mo₂B₅, Cr(Co(Mo, and FeCr_0.29Ni_0.16C_0.06 phases. Wear tests indicate that the gradient coating has good bond strength and wear properties with a wear coefficient of 0.31 (0.50 for the Cu alloy substrate). Also, the wear loss of the coating is only 0.01 g after it has been abraded for 60 min, which is only one fifth of that of the Cu alloy of the crystallizer. Wear tests of the gradient coating reveal good adhesive friction and wear properties when sliding against steel under dry conditions. This novel technique may have good application to make an advanced coating on the surface of the Cu alloy crystallizer in a continuous casting process.     

First-principles calculations to investigate half-metallic ferromagnetism in Zn0.50Ti0.50S alloy by using DFT + U calculations

ABSTRACT

The spin-polarized structural, electronic and magnetic properties of the Ti-doped zincblende ZnS compound at x?=?0.50 (Zn_0.50Ti_0.50S alloy) have been investigated by employing the first-principles full-potential linearised augmented plane wave with local orbitals (FP-L/APW?+?lo) method within the frame-work of spin-polarized density functional theory (spin-DFT). For the treating of the structural properties, the electronic exchange and correlation (XC) functional was defined by generalised gradient approximation (GGA), whereas both GGA and GGA?+?U approximations are applied to treat and to compare the electronic and magnetic properties (U is the Coulomb repulsion energy). It has been confirmed that the ferromagnetic (FM) state of this alloy is found the most stable phase; however, all the equilibrium lattice parameters such as; lattice constant (a₀), bulk modulus (B₀), and its first-pressure derivative (B′) are computed in all paramagnetic, ferromagnetic and anti-ferromagnetic phases. The calculations of electronic properties unveil the perfect half-metallic character in the tetragonal Zn_0.50Ti_0.50S system. The computed magnetic properties reveal that the total magnetic moment is mainly originated from the transition element (TM) of Ti. Moreover, we have found that the p-d hybridisation is the paramount responsible for the reduction of the magnetic moment of TM from its free space charge value and for the production of minor magnetic moments on the nonmagnetic Zn and S sites.     

Effect of Gd2O3 on the hydrogen evolution property of nickel–cobalt coatings electrodeposited on titanium substrate

The effect of rare earth compound, Gd₂O₃, on the microstructure and the hydrogen evolution property of Ni–Co alloy electrode was studied. The morphology and microstructure were characterized by SEM and XRD, respectively, and the electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from steady-state polarization curves, Tafel curves and electrochemical impedance spectroscopy measurements carried out in 0.50 M Na₂SO₄+0.10 M H₂SO₄ solution. It was found that the embedded Gd₂O₃ particles largely enhanced the electrocatalytic activity of Ni–Co alloy electrode to hydrogen evolution reaction.     

Dopant activation in Sb-implanted relaxed Si1−xGex alloy layers grown on compositionally graded buffers

Supersaturated solid solutions of substitutional, electrically active Sb have been obtained by ion implantation of relaxed epitaxial Si_1?xGe_x alloy layers grown on compositionally graded buffers. Substitutional and nonsubstitutional Sb fractions in relaxed Si_0.85Ge_0.15, Si_0.65Ge_0.35 and Si_0.50Ge_0.50 alloy layers implanted to a dose of 5×10¹⁵ Sb cm^?2 and annealed isothermally at temperatures ranging from 400 to 850°C have been studied by Rutherford backscattering/channeling, transmission electron microscopy and Hall-effect and sheet resistivity measurements. A supersaturated solution of Sb corresponding to a peak carrier concentration of 4×10²⁰ cm^?3 and an electrically active fraction of 40% of the implanted dose is observed by Hall measurements for the case of Si_0.85Ge_0.15 and Si_0.65Ge_0.35 alloys annealed at 550°C.     

Studies on the valence electronic structure of Fe and Ni in Fe x Ni1−x alloys

K _β-to-K _α X-ray intensity ratios of Fe and Ni in pure metals and in Fe _x Ni_1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a ²⁴¹Am point source, to understand as to why the properties of permalloy Fe_0.2Ni_0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe_0.2Ni_0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.     

(Pt3Co)1-xNix合金薄膜的结构、磁性和磁光特性研究

采用直流溅射的方法,在Pt₃Co合金靶上加贴Ni片,把（Pt₃Co)_1-xNi_x合金薄膜中非磁性原子与磁性原子的比率从3：1调制到1：1.通过高角X射线衍射谱和磁性的研究,发现<111>织构至少在0.33—0.50的Ni成分范围内不是引起垂直磁各向异性的主要原因.在此基础上研究了(Pt₃Co)_1-xNi_x合金薄膜的磁光特性.研究表明,适量Ni合金化（x=0.43)可以获得较低的(Pt₃Co)_1-xNi_x合金薄膜居里温度,同时保持较高的垂直磁各向异性、较大的矫顽力和蓝波长下较高的Kerr转角,从而为PtCoNi合金薄膜的实用化提供了实验参考. 关键词：     

The influence of pH and bath composition on the properties of Fe-Co alloy film electrodeposition

Fe-Co films were electrodeposited on ITO glass substrates from the electrolytes with different molar ratio of Co²⁺/Fe²⁺ and different pH values (2.1, 2.9, 3.7, and 4.3) at 25 °C. The properties of Fe-Co alloy films depend on both Co²⁺ and Fe²⁺ concentrations in electrolyte and pH values was studied. The content of Co increases from 40% to 85% as the mole ratio of CoSO₄/FeSO₄ increasing from 0.50/0.50 to 0.90/0.10 in electrolyte and slightly decreases from 77% to 63% as the pH values increasing from 2.1 to 4.3. The X-ray diffraction analysis reveals that the structures of the films strongly depend on the Co content in the binary films. The surface morphologies of the films are influenced by the combined action of composition and phase structure. The saturation magnetization reaches a maximum value of 2974.03 emu/cm³ and coercivity reaches a minimum value of 42.72 Oe of the Fe_0.30Co_0.70. The saturation magnetization reaches a maximum values of 2974.03 emu/cm³ and coercivity reaches a minimum values of 42.72 Oe of the Fe_0.30Co_0.70 at pH = 2.9.     

The influence of oxygen vacancies on the magnetic state of La<Subscript>0.50</Subscript>D<Subscript>0.50</Subscript>MnO<Subscript>3−γ</Subscript> (D=Da,Sr) manganites

The crystal structure and magnetic and electric transport properties of polycrystalline La_0.50D_0.50MnO_3?γmanganites (D=Ca, Sr) were studied experimentally depending on the concentration of oxygen vacancies. The La_0.50Sr_0.50MnO_3?γ system of anion-deficient compositions was found to be stable and possess a perovskite structure only up to the γ=0.25 concentration of oxygen vacancies, whereas, for the La_0.50Ca_0.50MnO_3?γ system, we were able to obtain samples with the concentrations of oxygen vacancies up to γ=0.50. The stoichiometric La_0.50D_0.50MnO₃ (D=Ca, Sr) compositions had O-orthorhombic (Ca) and tetragonal (Sr) unit cells. The unit cell of the anion-deficient La_0.50Sr_0.50MnO_3?γ manganites also became O-orthorhombic when the concentration of oxygen vacancies increased γτ;0.16). Oxygen deficiency in La_0.50Sr_0.50MnO_3?γ first caused the transition from the antiferromagnetic to the ferromagnetic state γ～0.06) and then to the spin glass state γ～0.16). Supposedly, the oxygen vacancies in the reduced La_0.50Sr_0.50MnO_{3? γ} samples with γ≥0.16 were disordered. The special feature of the La_0.50Ca_0.50MnO_3?γ manganites was a nonuniform distribution of oxygen vacancies in the La_0.50Ca_0.50MnO_2.75 phase. In the La_0.50Ca_0.50MnO_2.50 phase, the type of oxygen vacancy ordering corresponded to that in Sr₂Fe₂O₅, which led to antiferromagnetic ordering. The specific electric resistance of the La_0.50D_0.50MnO_3?γ anion-deficient samples increased with increasing oxygen deficiency. The magnetoresistance of all samples gradually increased as a result of the transition to the magnetically ordered state. Supposedly, the La_0.50Ca_0.50MnO_3?γ manganites in the range of oxygen vacancy concentrations 0.09≤γ≤0.50 had a mixed state and contained microdomains with different types of magnetic ordering. The experimentally observed properties can be interpreted based on the model of phase layering and the model of superexchange magnetic ordering.     

Local-order hypotheses and atomic arrangement in the glassy alloy As0.45Se0.05Te0.50 by X-ray diffraction

Summary The radial atomic distribution of the amorphous alloy As_0.45Se_0.05Te_0.50 was studied through the X-ray diffraction data supplied by samples obtained through quenching. The short-range order was determined by interpreting the radial distribution function (RDF), using a theoretical expression which takes into account the variation in the atomic scattering factors withs (the scattering vector module), and approximates them to polynomic functions. The tetra- and tri-coordinated arsenic hypotheses, quoted in the literature for glassy alloys containing this element, were considered. The result of the study is that, for the alloy in question, only the tri-coordinated arsenic hypothesis is compatible with the structural information that was experimentally obtained. A spatial atomic distribution model was generated according to this arsenic coordination, using the conveniently modified Monte Carlo random method. The model is a network of triangular pyramids with arsenic atoms at some vertices. A comparative analysis of the main structural parameters of this model revealed their good agreement with the values given in the literature for similar alloys.     

Spin-wave scattering from A γ-Fe47Mn53alloy

Spin waves in the antiferromagnetic alloy γ-Fe_0.5Mn_0.5 have been studied at $\text{295° K(}\text{T}\text{T}{}_{\mathrm{N}}\text{= 0.63)}$ by the inelastic neutron scattering technique. We observed an isotropic dispersion and obtained a value for the spin-wave velocity of 255 ± 30 meV Å (3.88 ± 0.50 × 10⁶ cm/sec), which is the order of the spin-wave velocity in Cr (a typical itinerant antiferromagnet). The energy gap at q = 0 was found to be 7.0 ± 0.5 meV. These results suggest the existence of a long-range spin ordering in the conduction electrons of this alloy.     

In situ Mössbauer studies of vapor quenched Ag/Fe and Au/Fe films

Metastable alloys of Ag_1-xFe_x (x=0.17, 0.30, 0.50, 0.54, 0.56 and 1.0) and the stable Au_1-yFe_y (y=0.18 and 0.25) alloy were prepared as thin films by vapor quenching method on low temperature kapton substrate. The X-ray diffraction spectra of all Ag/Fe samples. withx<-0.56, have indication of fee structure with very small grain size. The present work reports in-situ Mössbauer results on Ag/Fe and Au/Fe films. The spectra obtained are characteristic of homogeneous disordered alloy with broad magnetic hyperfine field distribution. Aging effect inducing cluster formation was observed in Ag/Fe films after they were heated to room temperature, but this behavior was not detected in Au/Fe samples.     

Effect of the size factor on the magnetic properties of manganite La0.50Ba0.50MnO3

Nanocrystalline manganite La_0.50Ba_0.50MnO₃ was synthesized by an optimized sol-gel method. The initial sample was subjected to step-by-step heat treatment under air atmosphere. The ion stoichiometry, the morphology of crystallites of ceramics, and the magnetic properties were studied. It is established that the average crystallite size D increases from ～30 nm to ～7 μm with increasing annealing temperature. All of the samples studied are characterized by a perovskite-like cubic structure, with the unit cell parameter a increasing continuously from ～3.787 to ～3.904 Å with the average crystallite size. The most significant lattice compression (≈3%) occurs in the sample with an average crystallite size of ～30 nm. The increase in the average crystallite size causes a nonmonotonic increase in the Curic temperature T _C from ～264 to ～331 K and in the spontaneous magnetic moment σ _S from ～1.52 to ～3.31 μ_B/f.u. The anomalous behavior of the magnetic properties of the manganite La_0.50Ba_0.50MnO₃ obtained is explained by the competition between two size effects, namely, the frustration of the indirect exchange interactions Mn³⁺-O-Mn⁴⁺ on the nanocrystallite surface and the crystal lattice compression due to the crystallite surface tension.     

Investigation of magnetic phase transformations in a system of Nd1−x BaxMnO3−δ (0≤x≤0.50) depending on the conditions of preparation

Investigations are performed of the crystal structure and magnetic and electromagnetic properties of single crystals (0.23 ≤x≤0.34) and polycrystals (0 ≤x ≤0.50) of an Nd_1?x Ba_xMnO_3?δ system of solid solutions. It is found that, for samples prepared in the air, the maximal Curie temperature (T _C ) does not exceed 150 K, while, in the case of polycrystalline samples in the concentration range of 0.34 ≤x ≤0.50, prepared in a reducing medium (a gaseous mixture of argon and carbon monoxide), T _C increases to 320 K. As a result of the reducing medium effect on the compositions, the type of the magnetic phase transition to the paramagnetic state changes from the first to second order. The electrical resistivity of reduced polycrystalline samples (0.34≤x ≤0.50) decreases in magnitude and correlates with the behavior of magnetization. Both series of samples, prepared both in the air and in a reducing medium, exhibit a transition from the metal to dielectric state at a temperature below T _C . The temperature and field dependences of magnetization for the stoichiometric polycrystalline com-position of Nd_0.50Ba_0.50MnO₃ are measured under conditions of hydrostatic pressure. It is demonstrated that the hydrostatic pressure induces in Nd_0.50Ba_0.50MnO₃ the transition from the antiferromagnetic to ferromagnetic state. Based on the measurement results, hypothetical magnetic phase diagrams are constructed for the system of solid solutions being treated, depending on the concentration of barium and the method of preparation. It is found that no T _TC increase is observed in single crystals (0.23≤x≤0.34) such as is observed in polycrystals. It is assumed that the abrupt increase in T _C of polycrystalline samples prepared in a reducing medium is a result of the emergence of extended defects and microstresses in the crystal lattice.     

Correlation between long-wavelength magnetic excitations and an inhomogeneous magnetic structure in γ-FeNi alloys

An energy analysis of small-angle neutron scattering in Fe _x Ni_1?x (x = 0.50, 0.57, 0.65 at %) alloys is performed at various temperatures and wavevectors. Low-energy long-wavelength magnetic excitations other than spin waves of the Holstein-Primakoff type are detected. These data and the data obtained earlier for the Fe_0.65Ni_0.35 alloy indicate that the density of states of the low-energy long-wavelength magnetic excitations correlates with the inhomogeneity of the magnetic structure of the alloys, which is caused by the iron concentration and a competing exchange interaction (J _NiNi > 0, J _FeNi > 0, J _FeFe < 0).     

Studies on luminescence properties and energy transfer in Ce/Dy co-doped CaS nano-phosphors

Luminescence properties of CaS:Ce co-doped with dysprosium has been studied. Ce/Dy co-doped CaS nanophosphors (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50, CaS:Ce_0.75Dy_0.25) were synthesized using the solid state diffusion method. The phase purity of the samples was confirmed using XRD data. The particle size was calculated using Debye–Scherrer formula and was found to be varying between 50 and 60 nm for all the three samples (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50 and CaS:Ce_0.75Dy_0.25). TEM image analysis of CaS:Ce_0.50Dy_0.50 shows nearly spherical particles with diameter varying between 50 and60 nm. One way energy transfer from Dy³⁺ to Ce³⁺ in CaS host has been investigated using photoluminescence studies. Thermoluminescence of these nanophosphors has been studied for 0.5 Gy–21 kGy dose of gamma rays and the dose linearity of CaS:Ce_0.50Dy_0.50 has been compared with CaSO₄:Dy (standard TL dosimeter). Linear behavior over a large dose range between 0.5 Gy and 21 kGy was found for CaS:Ce_0.50Dy_0.50 as compared to CaSO₄:Dy (nanocrystalline and microcrystalline) but it is found to be less sensitive than microcrystalline CaSO₄:Dy. To identify the peaks of Ce³⁺ and Dy³⁺ in CaS, the TL spectra of CaS, CaS:Ce, CaS:Dy and CaS:Ce_0.50Dy_0.50 were recorded. The addition of dopants does not add new peaks in CaS but aid to enhance the TL emission. The peaks in CaS may be associated to intrinsic traps in the host lattice.     

Effect of the substitution of S for Se on the structure of the glasses in the system Ge0.23Sb0.07S0.70−xSex

Glasses in the system Ge-Sb-S/Se, expected to have high nonlinear index, have been elaborated with different S/Se ratio in order to increase the nonlinear optical properties of these glasses. We report results of a systematic study examining the relationship of the physical properties to the structure of the glasses in the system Ge_0.23Sb_0.07S_0.70−xSe_x with x=0, 0.05, 0.10, 0.20, 0.50 and 0.70 where the substitution of S for Se has been made. The decrease of the glass transition temperature and the increase of the density with the progressive substitution of S for Se have been correlated, in accordance with the red shift of the absorption band gap, to the progressive decrease of corner-sharing GeS_4/2 units for 0.05<x<0.50 and of the progressive increase of corner-sharing GeSe_4/2 units and Ge-Se-Ge when x>0.50.     

Magnetism in FeAl,CoAl, CoGa and NiAl

Isothermal magnetization vs field data from 1.6 to 300°K for Ni_0.48Al_0.52, Ni_0.50Al_0.50, Co_0.48Al_0.52 and Co_0.50Al_0.50 can be described in terms of contributions from magnetic clusters, from “antistructure” transition metal atoms on Al sites, and from a field- and temperature-independent susceptibility. The moment of antistructure Ni is 0.3μ_B in both nickel alloys. In both cobalt aluminides as well as in Co_0.47Ga_0.53, the antistructure Co moment is 1μ_B. The moment of antistructure Fe in Fe_0.49Al_0.51 is 2.2μ_B.     

Directional frustration of magnetic moments in (U0.50Dy0.50)Ni2B2C

Polycrystalline (U_0.50Dy_0.50)Ni₂B₂C solid solution was prepared and found by X-ray diffraction to crystallize in BCT LuNi₂B₂C-type structure (space group I4/mmm) of the end compounds UNi₂B₂C and DyNi₂B₂C. AC susceptibility and magnetization show paramagnetic behavior down to 6.5 K, with the values θ=−5(5) K and μ_eff=7.7(1) μ_B, compatible with those of the end compounds, and indicate possible cooperative phenomena at lower temperatures. The observed paramagnetism, at variance with antiferromagnetic ordering in (Pr_0.50Dy_0.50)Ni₂B₂C, is attributed to a directional frustration of the magnetic moments on the (U,Dy) site.