The Effect of Ge, Ni, and Fe Doping on the Ga Activity in the CoGa B2 Phase

Gallium activity in the B2 (CsCl-type) phase of ternary Co–Ga–X (X = Ge, Ni, and Fe) alloys was measured by the EMF method with a stabilized zirconia solid electrolyte. The temperature range was 1050–1250 K and the concentrations of the added elements were 2–6 at-% Ge and Ni, and 1–3 at-% Fe. The reference electrodes were Fe,Fe_xO or Ga,Ga₂O₃. The effect on the activity of gallium in the B2 phase with the addition of other elements was found to be the largest with Ge and the smallest in the case of Ni.     

Electrodeposition and characterization of zinc–nickel–iron alloy from sulfate bath: influence of plating bath temperature

The electrodeposition of ternary zinc–nickel–iron alloy was studied in acidic sulfate bath. The comparison between Zn, Ni, and Fe deposition and Zn–Ni and Zn–Ni–Fe co-deposition revealed that the remarkable inhibition of Ni and Fe deposition takes place due to the presence of Zn²⁺ in the plating bath. The increase in corrosion resistance of ternary deposits is not only attributed to the formation of γ-Ni₂Zn₁₁ phase but also to iron co-deposition and formation of iron phase. It was also found that the bath temperature has a great effect on the surface appearance and the deposit composition. The investigation was carried out using cyclic voltammetry and galvanostatic techniques for electrodeposition, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Morphology and chemical composition of the deposits were characterized by means of scanning electron microscopy and atomic absorption spectroscopy.     

Influence of Ni content on Fe–Nb–B alloy formation

In this work three alloys, Fe₇₄Nb₆B₂₀, Fe₆₄Ni₁₀Nb₆B₂₀ and Fe₅₄Ni₂₀Nb₆B₂₀, were obtained by mechanical alloying to analyze the influence of Ni content on Fe–Nb–B alloy formation. Structural analysis by X-ray diffraction (XRD) confirms that partial substitution of Fe by Ni favours the formation during milling of a more disordered structure. Furthermore, thermal stability study was performed by differential scanning calorimetry (DSC) because thermally induced structural changes can affect soft magnetic behaviour. After 40 h of milling time, all DSC curves show several exothermic effects on heating associated to structural relaxation and crystallization. All alloys present a crystallization process with associated activation energy values ranged between 238 and 265 kJ mol^–1 related to the crystalline growth of the bcc-Fe rich phase. In alloys with Ni, a second crystallization process appears at temperatures over 500°C with activation energies 397 (10% Ni alloy) and 385 kJ mol^–1 (20% Ni alloy) probably associated to the nucleation and crystalline growth of a new phase.     

Impact of Transition Metal Substituents on Polysilane Properties: Iron versus Ruthenium

Summary. The previously unknown ruthenio disilanes Rp–Si₂Me₄–C₆H₄X (Rp = η⁵-C₅H₅Ru(CO)₂; X = H, Br, –CHO, CH=C(CN)₂) were synthesized from ClSi₂Me₄C₆H₄X (X = H, Br) and Rp⁻ using conventional chemical methods. Trends in the UV/Vis absorption spectra indicate strong electronic coupling within the Rp–Si–Si–C_aryl fragment and, therefore, closely resemble the ones observed for the corresponding iron complexes. The four compounds however, were shown to be less sensitive towards UV irradiation. The crystal structure of Rp–Si₂Me₄–C₆H₄CH=C(CN)₂ was determined by X-ray diffraction and exhibits an all-trans-array of the Ru–Si–Si–C_aryl moiety, what is a basic requirement for optimal through-bond interaction.     

Phase Relations in the Ni–Mn–Ga Ternary System and Aging Effect on Shape Memory Properties of Ferromagnetic Ni<Subscript>2</Subscript>MnGa Sputtered Films

Summary. Isothermal sections of the Ni–Mn–Ga ternary phase diagram at 1073 and 1273 K were investigated over a wide range of alloy compositions. The range of the β-Ni₂MnGa phase, its equilibria with the γ-(Mn, Ni), α′-Ni₃Ga, and γ-Ni₃Ga₂ phases, and the liquidus and solidus lines were determined experimentally. The aging effect on the shape memory effect (SME) of Ni₂MnGa sputtered films was also investigated. The two-way SME of the constraint-aged films was confirmed by the temperature change.     

Determination of major, minor and trace elements in cobalt-substituted lithium nickelate ceramic powders by inductively coupled plasma optical emission spectrometry

An analytical method was developed for the determination of three major (Li, Ni and Co) and fourteen minor or trace elements (Al, Ba, Ca, Cu, Cr, Fe, K, Mg, Mn, Na, Si, Sr, Ti and V) in LiNi_1−x Co _x O₂ (x = 0.2–0.8) ceramic powders by inductively coupled plasma optical emission spectrometry. Sample dissolution was achieved by 25% nitric acid digestion in a microwave oven. For each element, an analytical line free from spectral interferences was selected. A detailed study of matrix effects over a wide interval of total excitation energy (TEE) lines (1.62–16.50 eV) was performed at near-robust plasma conditions. A remarkable enhancement in atomic lines with TEE <4 eV was noticed, whereas a significant reduction in atomic and ionic lines with TEE >4 eV was observed. The extrapolation to infinite dilution method was successfully used to overcome these nonspectroscopic interferences. Detection limits (3σ) varied from 0.21 mg kg⁻¹ for Sr to 49.7 mg kg⁻¹ for Na. The precision of determination (obtained as the relative standard deviation) was lower than 1% for the major elements Li, Ni and Co and between 0.69 and 10% for minor and trace elements. The accuracy of the method ranged from 91 to 101% for major elements, and from 90 to 110%, or close to this range, for most of the impurities in both of the samples studied.      

Aqueous germanate solution,alternative sol–gel precursor for preparation of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> diluted magnetic semiconductors

The solids content and gelation time of aqueous germanate solution were examined in this work. Samples of 5, 10 and 20 mol% Mn doped Ge were prepared by using the aqueous germanate solution as a liquid Ge precursor. No second phase such as Mn₅Ge₃ was detected in the 5 and 10 mol% Mn doped samples, implying that Mn ions were uniformly diluted into the Ge host matrix. The 5 and 10 mol% Mn-doped Ge samples exhibit room-temperature ferromagnetic behaviors that are likely originated from the RKKY (Ruderman–Kittel–Kasuya–Yosida)-like interaction between the localized Mn ions in the Ge matrix. Therefore, the aqueous germanate solution can be an alternative sol–gel precursor for preparation of the Mn _x Ge_1−x diluted magnetic semiconductors (DMSs).     

Sol–Gel Synthesis and Magnetic Studies of Titanium Dioxide Doped with 10% M (M=Fe,Mn and Ni)

TiO₂ nanocrystals doped with 1%, 5% and 10% Co/TiO₂ and 10% M (M=Fe, Mn and Ni) were prepared by the sol–gel technique and characterized using X-ray diffraction and SQUID. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) for the 5% Co/TiO₂ was observed by hydrogenating the sample at 573 K while the 1% sample remained paramagnetic. As the percentage of Co was increased from 5% to 10% the Curie temperature increased from 390 K to 470 K determined via extrapolation. Transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was also observed by hydrogenation of 10% Fe/TiO₂ at 573 K for 6 h. X-ray diffraction of the hydrogenated sample shows only single phase TiO₂ structure suggesting that the observed RTFM may be intrinsic but magnetic studies may suggest the possibility of Fe nanoparticles.     

Electrochemical reactivity of Li–Mn–O and Li–Fe–Mn–O spinels

Electrochemical reductive dissolution of Li–Mn–O and Li–Fe–Mn–O spinels and Li⁺ extraction/insertion in these oxides were performed using voltammetry of microparticles. Both electrochemical reactions are sensitive to the Fe/(Fe+Mn) ratio, specific surface area, Li content in tetrahedral positions, and Mn valence, and can be used for electrochemical analysis of the homogeneity of the elemental and phase composition of synthetic samples. The peak potential (E _P) of the reductive dissolution of the Li–Mn–O spinel is directly proportional to the logarithm of the specific surface area. E _P of Li–Fe–Mn–O spinels is mainly controlled by the Fe/(Fe+Mn) ratio. Li⁺ insertion/extraction can be performed with Mn-rich Li–Fe–Mn–O spinels in aqueous solution under an ambient atmosphere and it is sensitive to the regularity of the spinel structure, in particularly to the amount of Li in tetrahedral positions and the Mn valence. Electronic Publication     

Structure and stability of hypervalent NLi n Na2 (n = 1–4) and related species at density functional theory level

A number of configurations of NLi _n Na₂ (n = 1–4) species were optimized using the B3LYP–density functional theory method; the 6-31G^* basis set was used in this calculation. In order to study all possible dissociation energies, some related species such as NLi₂Na, NLi _n (n = 1–4), Li _n (n = 1, 2) and Na _n (n = 1, 2) were also considered. Optimizations of these species were followed by fundamental frequency calculations at the same level. Global minima of these species were shown to adopt C _{2 v} (NLi₄Na₂, NLi₂Na₂), D _{3 h} (NLi₃Na₂) and C _s (NLiNa₂ and NLi₂Na) configurations. All possible dissociation energies were obtained. Received: 30 November 1998 / Accepted: 15 October 1999 / Published online: 14 March 2000     

Thermodynamics of Structural Changes in Liquid Ge–Te Alloys Around the Eutectic Composition: Specific Heat Measurements and Thermodynamic Stability

Summary. We have obtained the specific heat, C_p, of liquid Ge–Te alloys around the eutectic composition (15 at.% Ge) and alloys up to 50 at.% Ge by combining the data obtained by modulation and adiabatic calorimetries. The results cover a wide temperature range from deeply undercooled state to 800°C. A very pronounced peak of C_p was observed for Te and alloys up to 20 at.% Ge. The peak position of C_p takes a maximum around the eutectic composition where the peak width becomes narrowest. Using a new thermodynamic relation, we clarify a correlation between the thermodynamic stability and structural changes in the liquid Ge–Te system.     

A small-core multiconfiguration Dirac–Hartree–Fock-adjusted pseudopotential for Tl – application to TlX (X = F, Cl, Br, I)

 A relativistic pseudopotential of the energy-consistent variety simulating the Tl²¹⁺ (1s– 4f) core has been generated by adjustment to multiconfiguration Dirac–Hartree–Fock data based on the Dirac–Coulomb–Breit Hamiltonian. Valence ab initio calculations using this pseudopotential have been performed for atomic excitation energies and for spectroscopic constants of the X0⁺ and A0⁺ states of TlX (X = F, Cl, Br, I). Comparison is made to experiment and to four-component density functional results. Received: 22 June 1999 / Accepted: 5 August 1999 / Published online: 15 December 1999     

A correlation-consistent basis set for Fe

 A series of correlation-consistent basis sets are developed for Fe. Our best computed ⁵F–⁵D separation in the Fe atom is in excellent agreement with experiment. Our best estimate for the FeCO D ₀ value is in good agreement with experiment. The ⁵Σ⁻–³Σ⁻ separation in FeCO has an error of 3.6 kcal/mol; while the origin of this error is not clear, it is probably not due to the basis set. Received: 5 March 2001 / Accepted: 2 May 2001 / Published online: 9 August 2001     

Ab initio and density functional theory studies on the mechanism of nucleophilic vinylic substitution of 4<Emphasis Type="Italic">H</Emphasis>-pyran-4-one and 2-methyl-4<Emphasis Type="Italic">H</Emphasis>-pyran-4-one with ammonia

 Nucleophilic vinylic substitutions of 4H-pyran-4-one and 2-methyl-4H-pyran-4-one with ammonia were calculated by the B3LYP method using the 6-31G(d,p) basis set. Bulk solvent effects of aqueous solution were estimated by the polarized continuum and Poisson–Boltzmann self-consistent reaction field models using the 6-311+G(d,p) basis set. In the gas phase different mechanisms were found for the two reaction systems calculated. The reaction of 4H-pyran-4-one proceeds through enol, whereas a feasible path for the less reactive 2-methyl-4H-pyran-4-one is the mechanism through a keto intermediate. Addition of ammonia in concert with proton transfer is the rate-determining step ofthe reaction. The mechanism proceeding either by a bimolecular nucleophilic substitution (S_N2) or by one involving a tetrahedral zwitterionic intermediate is shown to be unlikely in the gas phase or nonpolar solution. The effects of bulk solvent not only consist in a reduction of the various activation barriers by about 25–40 kJ mol⁻¹ but also in a change in the reaction mechanism. Received 26 May 2002 / Accepted 26 July 2002 / Published online: 14 February 2003     

Activity Measurements of Solid Ni–In Alloys by EMF Method with Zirconia Solid Electrolyte

Summary. The EMF of galvanic cells with stabilized zirconia solid electrolyte was measured to determine the activity of indium in solid Ni–In alloys in the temperature range of 970–1170 K and composition range of 5–55 mol% In. Activity of indium increases sharply in the ζ phase and Ni₁₃In₉ phase. The activity values are compared with literature data.     

Comparison of Prediction of Phase Equilibria in the Ag–In–Sb System at 200°C with Experimental Data

Summary. Binary thermodynamic data, successfully used for phase diagram calculations of binary systems Ag–In, Ag–Sb, and In–Sb, were used for prediction of phase equilibria in ternary Ag–In–Sb system at 200°C. Symmetrical Redlich–Kister–Muggianu model for ternary thermodynamic function calculation was proved to be best valid in this ternary system. Predicted equilibria were compared with experimentally (SEM, EDX) determined composition of phases in chosen alloys after long term annealing and with the results of DTA measurements.     

Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

 Combined analytical procedures consisting of wet digestion step followed by instrumental determination – differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) – as well as a direct analysis method – slurry sampling ETAAS – for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO₃-HClO₄-H₂O₂ is proposed for complete matrix decomposition prior to trace analyte determinati on by DPCSV or ETAAS. A mixture of HNO₃-H₂O₂ is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5–10% for wet digestion DPCSV or ETAAS and 3–9% for slurry sampling ETAAS in the range of 2 μgċg⁻¹ (Cd) to 12 μgċg⁻¹ (Fe). Received August 24, 1999. Revision January 20, 2000.     

An atom-in-molecules and electron-localization-function study of the interaction between O2 and VxOy+/VxOy (x = 1, 2, y = 1–5) clusters

 The most stable structures of V _x O _y ⁺/V _x O _y (x=1, 2, y=1–5) clusters and their interaction with O₂ are determined by density functional calculations, the B3LYP functional with the 6-31G* basis set. The nature of the bonding of these clusters and the interaction with O₂ have been studied by topological analysis in the framework of both the atoms-in-molecules theory of Bader and the Becke–Edgecombe electron localization function. Bond critical points are localized by means of the analysis of the electron density gradient field, ∇ρ(r), and the electron localization function gradient field, ∇η(r). The values of the electron density properties, i.e., electron density, ρ(r), Laplacian of the electron density, ∇²ρ(r), and electron localization function, η(r), allow the nature of the bonds to be characterized, and linear correlation is found for the results obtained in both gradient fields. Vanadium-oxygen interactions are characterized as unshared-electron interactions, and linear correlation is observed between the electron density properties and the V–O bond length. In contrast, O₂ units involve typical shared-electron interactions, as for the dioxygen molecule. Four different vanadium–oxygen interactions are found and characterized: a molecular O₂ interaction, a peroxo O₂ ²⁻ interaction, a superoxo O₂ ⁻ interaction and a side-on O₂ ⁻ interaction. Received: 15 October 2001 / Accepted: 30 January 2002 / Published online: 24 June 2002     

Ab initio calculations for the potential curves and spin–orbit coupling of Mg2

 The ground state and several low-lying excited states of the Mg₂ dimer have been studied by means of a combination of the complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS multireference second-order perturbation theory (CASPT2) method and coupled-cluster with single and double excitations and perturbative contribution of connected triple excitations [CCSD(T)] scheme. Reasonably good agreement with experiment has been obtained for the CCSD(T) ground-state potential curve but the dissociation energy of the only experimentally known A¹Σ _u ⁺ excited state of Mg₂ is somewhat overestimated at the CASSCF/CASPT2 level. The spectroscopic constants D _e, R _e and ω_e deduced from the calculated potential curves for other states are also reported. In addition, some spin–orbit matrix elements between the excited singlet and triplet states of Mg₂ have been evaluated as a function of internuclear separation. Received: 10 May 2001 / Accepted: 15 August 2001 / Published online: 30 October 2001