Study of the crystallography of slip in the alloy Ni3Al

It has been established that cubic slip is an effective mechanism for the strain of the Ni₃A1 alloy even at room temperature. Traces of cubic slip were observed in an electron microscope for all degrees of strain. The critical spalling stress in the plane of the cube is small and approximately 2.5 kg/mm². In a two-phase alloy consisting of segregations, '-phase (Ni₃Al) and a disordered matrix (-phase), the traces of cubic slip generated in the ordered phase which have reached the phase boundary, are even continued into the segregations of the disordered phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 7, pp. 42–47, July, 1971.     

Structural transformations in the alloy EI702

The structural transformations in the dispersion-hardening alloy EI702 have been investigated by the electrical resistivity method. The activation energies for the various stages in the change of electrical resistivity have been determined by the Meechan-Brinkman and Kauffman-Koehler methods. The activation energies obtained lead to the conclusion that short-range ordering takes place during annealing of the alloy in question. Further change in the electrical resistivity is associated with the formation of locally ordered segregations enriched to the composition (Ni,Fe)₃(Ti,Al) and with the development of dispersion hardening.     

Effect of the chemical composition on amorphization of titanium-nickelide-based alloys with fast neutrons

The structural state of a Ti₅₀Ni₄₇Fe₃ single crystal irradiated with fast neutrons (F = 2.5 × 10²⁰ cm^?2) at a temperature of 340 K was studied using thermal neutron diffraction. The alloy of this chemical composition was chosen in searching for a radiation-resistant shape memory material. It is established that this alloy retains its crystalline state after irradiation, whereas the Ti₄₉Ni₅₁ crystal studied previously is completely amorphized after similar irradiation. A detailed analysis of the structural state of the irradiated ternary alloy allowed us to discover the main physical causes of its radiation resistance.     

Influence of growth and anneal conditions on the surface roughness of L10 Fe50PdxPt50−x thin films

We deposit Fe₅₀Pd_xPt_50−x alloy thin films by magnetron sputtering onto a TiN seed layer. Chemically ordered L1₀ films are obtained which display large perpendicular magnetic anisotropy. We find that the surface roughness of the film depends strongly on the growth and anneal conditions as well as the Pd composition of the film. Smooth films are obtained by deposition above the chemical ordering temperature and by removing Pd from the alloy.     

A study of thermal parameters of Ag50Pd50 alloy using X-ray diffraction

Thermal parameters of Ag₅₀Pd₅₀ alloy were studied using the in-situ X-ray diffraction (XRD) technique. Diffraction experiments in the temperature range 308-1178 K showed that the alloy forms a face centered cubic (fcc; A1-type) structure. Temperature dependence of the lattice parameter was investigated using the Bragg line displacement method. Results show that the lattice parameter for the alloy increases with increase in temperature. The temperature dependent XRD data was utilized to determine the mean linear thermal expansion (MLTE (%)) and coefficient of thermal expansion (CTE) ‘α’ in the mentioned temperature range. It was observed that the values of CTE vary between 9.3 and 14.6 [K⁻¹][10⁻⁶]. The same data was also utilized to determine the Debye temperatures Θ_D and mean square amplitude of vibration (MSAV) (u²(T)) for this alloy. Values of thermal parameters as determined in this investigation are in good agreement with the estimated values as well as with those for other alloys of noble metals.     

First-principles calculations on the role of Ni-doping in Cun clusters: From geometric and electronic structures to chemical activities towards CO2

First-principles calculations have been applied to investigate the role of Ni-doping in modifying the geometric and electronic structures of Cu_n clusters (n=1-12), and the chemical activity of clusters towards CO₂. The results reveal that Ni-doping introduces a significant modulation of the electronic structures, such as the density of states, HOMO-LUMO gaps and the d-band centers, which dominate their chemical activities towards CO₂ adsorption. Our findings contribute valuable information for high efficient Cu-Ni alloy nano-catalyst design.     

Investigations of binary lithium-zinc,lithium-cadmium and lithium-lead alloys as negative electrodes in organic solvent-based electrolyte

The thermodynamic properties of the binary LiZn, LiCd and LiPb alloy systems were investigated in an organic solvent-based electrolyte at ambient temperature. Titration curves showed several intermediate phases existing in each lithium alloy system. There was a wide composition range in Li_yCd (1.5 ⩽ y ⩽ 3), which showed a very low equilibrium potential (below 60 mV) against pure lithium. There was a longer potential plateau in the LiPb system corresponding to Li_yPb (1 ⩽ y ⩽ 3) at about 450 mV against pure lithium. The preliminary charge-discharge and polarization results showed rather fast kinetics for Li_yZn (0.67 ⩽ y ⩽ 1), Li_yCd (1.5 < y < 2.0), and Li_yPb (1 < y < 3).     

Theoretical study of CuxAg1−xI alloys

We have performed first-principles calculations using full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT) to investigate the fundamental properties of Cu_xAg_1−xI alloys. We used both GGA96 [J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865.] and EVGGA [E. Engel, S.H. Vosko, Phys. Rev. B. 47 (1993) 13164.] generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential. Quantities such as lattice constants, bulk modulus, band gap, density of occupied states and effective mass were calculated as a function of copper molar fraction x. These parameters were found to depend non-linearly on alloy composition x, except the lattice parameter, which follows Vegard's law. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers; we have concluded that the band-gap energy bowing was mainly caused by the chemical charge-transfer effect and the volume deformation , while the structural relaxation contribute to the gap bowing parameter at smaller magnitude. The calculated phase diagram shows a broad miscibility gap for this alloy with a high critical temperature.     

Crystal structure and physical properties of magnetic shape memory alloys Ni50 − x Cu x Mn29Ga21

The phase composition, crystal structure, and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of the stoichiometric alloy Ni₅₀Mn₂₅Ga₂₅ and nonstoichiometric alloys Ni_{50 ? x} Cu _x Mn₂₉Ga₂₁ (x = 0, 1, 2) with the thermoelastic martensitic transformation have been investigated. The influence of the chemical composition on the transformations and physical properties of the alloys has been determined.     

Fine structure and mechanical properties of the shape-memory Ni<Subscript>50</Subscript>Ti<Subscript>32</Subscript>Hf<Subscript>18</Subscript> alloy rapidly quenched by spinning

We have reported the results of investigations of the structure and chemical and phase compositions of the amorphous Ni₅₀Ti₃₂Hf₁₈ alloy prepared by rapid quenching from melt by spinning and subjected to heat treatments. The specific features of the fine polycrystalline alloy structure formation depending on the heat-treatment mode have been studied by transmission and scanning electron microscopy, chemical microanalysis, electron diffraction, and X-ray diffraction analysis. According to the data on the temperature behavior of electrical resistivity, critical temperatures of devitrification and subsequent thermoelastic martensitic transformation B2 → B19′ have been determined. The mechanical properties in different heat-treatment modes have been investigated.     

The effect of the violation of Vegard's law on the optical bowing in Si1 − xGex alloys

The effect of the deviation of the lattice parameters from Vegard's rule on the optical bowing of the fundamental gap in Si_{1 − x}Ge_x semiconductor alloys is discussed. Our computations are based on the pseudopotential method. To make allowance for the chemical disorder, the virtual-crystal approximation is used, including a correction to the alloy potential. Our results show that the bowing parameter is highly improved when the lattice relaxation effect is included which indicates the importance of the lattice mismatch in the electronic band structure calculations of IV-IV semiconductor alloys.     

Band-gap bowing calculation of SixSn1−x alloy

Using ab initio pseudopotential method within the local density approximation we have investigated the electronic properties of Si_xSn_1−x semiconducting alloy. The bowing parameter of the band-gap energy variation with alloy concentration is found to be large. We also analyzed its origin in terms of chemical and structural effects.     

Properties of CuIn(SxSe1−x)2 polycrystalline thin films prepared by chemical spray pyrolysis

CuIn(S_xSe_1−x)₂ thin polycrystalline films were grown by the chemical spray pyrolysis method on the glass substrate at 280-400°C. The alloy composition in the film was studied with relation to that in the splay solution. Films were characterized by X-ray diffraction, optical absorption, Raman spectroscopy, resistivity and surface morphology. The CuInSe₂-rich alloy films grown at high substrate temperature had chalcopyrite structure, while, the CuInS₂-rich films grown at low substrate temperature exhibited sphalerite structure. Optical-gap energies were smaller than that of the bulk crystal by 0.1-0.2 eV for CuInS₂-rich films. Raman spectra exhibited both CuInSe₂-like and CuInS₂-like A₁ modes, and their relative changed systematically with alloy composition.     

Photoemission studies of a clean and oxidized niobium-aluminum alloy using synchrotron radiation

The alloy formation and oxidation of a Nb-rich Nb-Al alloy has been studied using core level photoemission in combination with synchroton radiation as a surface sensitive probe. Exactly the same chemical shifts were observed from both the Nb-Al alloy and an Al-evaporated Nb surface, indicating similar structural arrangements. It is found that the oxidation rate of Nb in these structures is drastically decreased in comparison to either pure Nb metal or Nb₃Sn. Two stages in the oxidation of the Nb-Al alloy are clearly distinguished by chemical shifts of the Al_2p, Nb_4p and O_2p levels.     

First-principles calculations on the origins of the gap bowing in InAs1-xPx alloys

We perform self-consistent ab-initio calculations to study the structural, electronic and thermodynamic properties of InAs_1-xP_x alloy. The full potential-linearized augmented plane wave (FP-LAPW) method was employed within density functional theory (DFT). The ground-state properties are determined for the bulk materials (InAs and InP) as well as for the different concentration of their alloys. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The gap bowing for the alloy of interest was found to be mainly caused by the charge-exchange contributions. In addition, the thermodynamic stability of InAs_1-xP_x alloy was investigated by calculating the excess enthalpy of mixing ΔH_m and the calculated phase diagram showed a broad miscibility gap with a high critical temperature.     

Segregation and adsorption of sulphur on Ni50Fe50(100) alloy: Studies of the surface composition and structure and of the effects on the passivation

The surface composition of Ni₅₀Fe₅₀(100) alloy was studied and the segregation and adsorption of sulphur were investigated by AES, LEED and radiotracer (³⁵S) techniques. Ion etching produces a surface composition identical to the matrix composition (Ni:Fe=1:1). In the temperature range 300–600°C iron segregates on the surface and nitrogen was detected. Heating to higher temperatures (>600°C) also causes the segregation of iron as well as the segregation of sulphur. The durface reaches a stable composition that does not depend on further changes of the temperature in the range 25–800°C. It consists of an almost complete monolayer of iron segregated on the alloy. The segregation of sulphur leads to the formation of a c(2×2) structure. A sulphur coverage of 45 ng cm^-2, consistent with the c(2×2) structure, was measured by the radiotracer method after chemisorption in gaseous H₂S/H₂ mixtures at 550° and 200 Torr. This sulphur monolayer is stable in a range of p_H2S/p_H2=7.4 × 10^-5-6×10^-4. Above this pressure, a preferential sulphidation of iron is observed. The effects of sulphur on the anodic dissolution and passivation of the alloy in acid solution were studied. Adsorbed sulphur promotes the dissolution and delays the passivation. When the alloy is doped with sulphur, bulk sulphur accumulates on the surface during the dissolution of Ni and Fe. This anodic segregation leads to the formation of an adsorbed layer of sulphur, followed by the growth of a sulphide which blocks the formation of the protective oxide film.     

Magnetic and electronic studies in the granular (Ni0.84Fe0.16)54(alumina)46 sputtered thin films

We have studied the magnetization in the granular (Ni_0.84Fe_0.16)₅₄(alumina)₄₆ alloy. The thermomagnetization curve is found to obey the Bloch law. Spin wave stiffness constant D and the exchange constant A were calculated from the experimental results. The magnetic experimental measurements have been interpreted in the framework of random magnetic anisotropy (RMA) model. The results have shown that it is possible to extend the application of RMA to the granular alloy. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. In addition, self-consistent ab initio calculations, based on Korringa–Kohn–Rostocker (KKR), are performed to investigate magnetic and electronic properties of the granular alloy. Spin polarization within the framework of the coherent potential approximation (CPA) is considered.     

Magnetic and electrical properties of the half-metallic ferromagnets Co2CrAl

This paper presents the results of measurements of the magnetic and electrical properties of the ferromagnetic alloy Co₂CrAl in two structural states: (i) after severe plastic deformation and (ii) after shortterm high-temperature annealing of the deformed specimens. The experiments have been performed at temperatures in the range from 2 to 900 K in magnetic fields H ≤ 50 kOe. The ferromagnetic Curie temperature T _C and the paramagnetic Curie temperature Θ have been determined (T _C = 305 K and Θ = 326 K), as well as the spontaneous magnetic moment μ _S and the effective magnetic moment μ_eff per molecule of the alloy (μ _S = 1.62 μ_B and μ _eff ² = 8.2 μ _B ² ). It has been shown that the magnetic crystalline anisotropy energy of the alloy is on the order of ～5 × 10⁵ erg/g. The specific features of the electrical properties are associated with the presence of an energy gap in the electronic spectrum near the Fermi level E _F and with the change in the parameters of the energy gap as a function of the temperature.     

On the selective catalytic behaviour of the Cu-NI alloy surface

The selective catalytic behaviour of the Cu_xNi_1?x alloy surface is studied. The concentration dependence of the catalytic activity with respect to chemical reactions involving cracking and non-cracking of C-C bonds is calculated for a simple model for C-C bonds. Surface segregation and local environment effects on chemisorption both calculated from a microscopic electronic theory using tight-binding approximation are taken into account.