Ordering of atoms in 3d sublattice of the intermetallic quasibinary system Dy(Fe1−xMnx)2

Methods of x-ray analysis and nuclear -resonance (Mössbauer effect) have been used to study the distribution of iron and manganese atoms in the intermetallic quasibinary system Dy(Fe_1–xMn_x)₂, which is isostructural to the Laves phase C15. Ordering of atoms of transition metals has been found in 3d sublattice of intermetallic compounds Dy(Fe_1–xMn_x)₂ with the formation of a triple superstructure having the stoichiometric composition Dy(Fe_0·.25Mn_0·.75)₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 55–60, June, 1986.     

Novel ternary iron-rich,rare-earth iron silicides: R3(Fe1−x Si x )22 (x ∼ 0.16)

In our search for new ternary rare-earth (R) iron silicon intermetallic compounds, a novel ternary phase with the chemical formula R₃Fe_18.5Si_3.5 has been identified with the RFeSi ratio in the range of 12–1574–7810–12. We have studied compounds with R=Gd, Tb, Dy, Ho, Er, Tm and Lu. All of the samples, except for R=Lu, form the new ternary phase3–22. X-ray diffraction data suggest that for R=Gd and Tb, the crystal structure is the rhombohedral Th₂Zn₁₇-type structure and for R=Dy, Ho, Er and Tm, the hexagonal Th₂Ni₁₇-type structure. We suggest that a 1/4 replacement of the R sites by Fe(Si) dumbbells in the CaCu₅-type structure leads to the new3–22 phase, which is an ordered version of the TbCu₇-type structure.⁵⁷Fe Mössbauer spectroscopy has been used to determine the hyperfine parameters of the⁵⁷Fe nuclei in the3–22 compounds. At 295 K, the average hyperfine field of the new3–22 phase ranges from 19.8 T (R=Ho) to 22.2 T (R=Gd). Thermogravimetric analysis (TGA) of these compounds gives Curie temperatures in the range 467 K (Tm)–549 K (Gd). Furthermore, our Mössbauer analysis enables us to investigate the preferential site occupancy shown by Si in these structures.     

Hydrogenation of Zr2Ni

The intermetallic compound Zr₂Ni has been found to take up hydrogen on charging at room temperature. Zr₂(NiFe) H_4.7 and Zr₂(NiFe) H_4.5 show the same structure (CuAl₂ type) as the uncharged compound but with an expanded lattice.Analysis of room temperature spectra in zero and applied fields indicates that the⁵⁷Fe atoms occupy Ni sites in Zr₂(Ni ⁵⁷Fe). Volume expansion effects account for about one third of the increase in isomer shift ( +0.58 mms^–1) observed on hydrogenation. The distribution of hydrogen atoms around the probe³⁷Fe atoms also causes a decrease of 0.23 mms^–1 in the mean value for the quadrupole splitting compared Rith uncharged Zr₂Ni.     

Temperature dependence of resistance to micro- and macrodeformation in precipitation-hardening Co-Ni-Ti and Co-Ni-Ti-Al alloys. II

The temperature dependence of mechanical properties (T) in the region of micro- and macroformations ( - 10^–6-10^–3) of the Co-Ni-Ti, and Co-Ni-Ti-Al alloys was studied in various structural states. It was shown that precipitation of Co³Ti phase in the alloy being investigated does not determine the anomalous temperature dependence (T) similar to that observed in various alloys with precipitation of Ni₃Al phase. Experimental data obtained indicated that temperature dependence of macroscopic yield point is determined by the dependence of the resistance to the onset of plastic flow on temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 52–57, September, 1972.     

Synthesis and characterization of a large amount of branched Ni2Si nanowires

A large amount of Ni₂Si nanowires sheathed with amorphous silicon oxide has been generated from Ni substrates, for the first time, by thermal chemical vapor deposition using SiH₄ gas at 500 °C. The Ni₂Si nanowires obtained possess substantial amounts of branches (about 2-m length) grown on the main stems (about -–30 80nm diameter and -–10 20m length). High-resolution transmission electron microscopy and electron diffraction have revealed the orthorhombic Ni₂Si phase and the orientation. At the tail end along the branch grown on a stem an amorphous phase was also observed. The Raman spectrum was further used to characterize the product. A possible growth process of the branched Ni₂Si nanowires is briefly discussed. PACS 81.05.Bx; 81.07.Bc; 81.15.Gh; 87.64.Ee; 87.64.Je     

Growth of Ni2Si by rapid thermal annealing: Kinetics and moving species

The growth kinetics is characterized and the moving species is identified for the formation of Ni₂Si by Rapid Thermal Annealing (RTA) of sequentially deposited Si and Ni films on a 100 Si substrate. The interfacial Ni₂Si layer grows as the square root of time, indicating that the suicide growth process is diffusion-limited. The activation energy is 1.25±0.2 eV in the RTA temperature range of 350–450° C. The results extend those of conventional steady-state furnace annealing quite fittingly, and a common activation energy of 1.3±0.2 eV is deduced from 225° to 450° C. The marker experiment shows that Ni is the dominant moving species during Ni₂Si formation by RTA, as is the case for furnace annealing. It is concluded that the two annealing techniques induce the same growth mechanisms in Ni₂Si formation.     

A new structure of In-based ohmic contacts ton-type GaAs

Electrical, structural and reaction characteristics of In-based ohmic contacts ton-GaAs were studied. Attempts were made to form a low-band-gap interfacial phase of InGaAs to reduce the barrier height at the metal/semiconductor junction, thus yielding low-resistance, highly reliable contacts. The contacts were fabricated bye-beam sputtering Ni, NiIn and Ge targets on VPE-grownn ⁺-GaAs film (1 m, 2 × 10¹⁸ cm^–3) in ultrahigh vacuum as the structure of Ni(200 Å)/ NiIn(100 Å)/Ge(40 Å)/n ⁺-GaAs/SI-GaAs, followed by rapid thermal annealing at various temperatures (500–900°C). In this structure, a very thin layer of Ge was employed to play the role of heavily doping donors and diffusion limiters between In and the GaAs substrate. Indium was deposited by sputtering NiIn alloy instead of pure In in order to ensure In atoms to be distributed uniformly in the substrate; nickel was chosen to consume the excess indium and form a high-temperature alloy of Ni₃ln. The lowest specific contact resistivity ( _c) of (1.5 ± 0.5) × 10^–6 cm² measured by the Transmission Line Method (TLM) was obtained after annealing at 700°C for 10 s. Auger sputtering depth profile and Transmission Electron Microscopy (TEM) were used to analyze the interfacial microstructure. By correlating the interfacial microstructure to the electronical properties, In _x Ga_{1– x}As phases with a large fractional area grown epitaxially on GaAs were found to be essential for reduction of the contact resistance.This work was supported by the National Natural Sciences Foundation of China (NSFC)     

Superconductivity and magnetic properties of Nb—Al phases: Nb2Al and NbAl3

Magnetic properties of tetragonal phases in Nb—Al system have been investigated down to 0.42°K. It has been found that the-phase (Nb₂Al) and the intermetallic compound NbAl₃ are superconductors with superconducting transition temperature 0.74°K and 0.64°K, respectively. Magnetic susceptibility of the investigated phases does not depend on temperature within the range 4.2°K–300°K, and is equal =(1.0±0.1) × 10^–6 emu)/g for Nb₂Al, and =(0.9±0.03) × 10^–6 emu/g for NbAl₃.On leave of absence from Institute for Solid State Physics of Bulgarian Academy of Sciences, Sofia, Bulgaria     

XRD and bulk magnetic studies on Ni-Cd and Ti doped Ni-Cd ferrites

For the ferrites Ni _x Cd_1–x Fe₂O₄ (x=0.3, 0.4,1) the lattice parameter, grain size, electrical resistivity, initial permeability, Curie temperature and squareness of the magnetization curve were measured. The results are discussed in terms of the model of the canted spin structure taking into account the domain structure of the polycrystalline ferrite.     

Hall effect in the ternary ordered alloys Ni3(Mn,Fe) and Ni3(Mn,Co) 1. Disordered solution solutions

The normal and anomalous Hall constants R₀ and R_s, respectively, and the resistivity have been measured for the quasibinary alloys Ni₃Mn-Ni₃Fe and Ni₃Mn-Ni₃Co. The results imply that in ternary alloys of Ni₃Mn containing slight Fe and Co impurities the hole regions of the Fermi surface make an important contribution to R₀ and that the primary scattering mechanism for the carriers corresponding to the anomalous Hall current in the alloys with Fe at room temperature is phonon scattering. It is concluded that the Fermi surface of the Ni₃Mn-Ni₃Fe alloys is closed.Translated from Izvestiya VUZ. Fizika, No. 3, pp. 21–29, March, 1970.     

On the magnetic behaviour of cadmium nickel ferrites

The magnetic behaviour of the mixed ferrite Cd_xNi_1–xFe₂O₄ system withx ranging from 0 to 0.9 are studied at different temperatures using the Mössbauer technique. The one-third power law and the empirical relation of the hyperfine magnetic fields (A-B) site dependence are verified. Néel points are determined for all compounds and the magnetic interactions are also discussed.     

Electric quadrupole interactions in Ru-Sc alloys

In TDPAC studies of the electric quadrupole interaction in Ru_xSc_1–x alloys two different electric fieldgradients (EFG) have been observed at the site of⁹⁹Ru: V_zz(I)=12.6·10¹⁷ V/cm² and V_zz(II)=18.9·10₁₇ V/cm². The corresponding relative fractions f(I) and f(II), respectively, vary with the Ru concentration x. For low concentrations x<0.01 most nuclei (f(I)0.8) experience the smaller EFG V_zz(I). At x=0.01, however, the fraction f(I) goes abruptly to zero and V_zz(II) becomes dominant. In view of these results the previous interpretation of V_zz(II) as the EFG of dilute Ru on substitutional Sc sites can no longer be maintained. The Ru-Sc configurations producing these EFG's have not yet been identified. In the intermetallic compound Ru₂Sc the interaction is completely different, in RuSc₃, however, similar values have been observed.     

Investigation of electrical resistivity and average magnetic moment per atom of Ni3(Fe,Ti) and Ni3(Mn,Ti) alloys

The electrical resistivity and average magnetic moment per atom of Ni₃(Fe, Ti) and Ni₃(Mn, Ti) alloys were measured. X-ray structural analysis revealed the presence of the Ni₃Ti phase in Ni₃(Fe+7% Ti) and Ni₃(Fe + 10.3% Ti), and strong interaction of Ni and Ti is deduced. The introduction of Ti into Ni₃Mn reduces the antiferromagnetic Mn-Mn interaction and thus leads to greater ordering.Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 9–12, May, 1981.     

Thermal equilibrium concentrations and effects of negatively charged Ga vacancies in n-type GaAs

We have calculated the thermal equilibrium concentrations of the various negatively charged Ga vacancy species in GaAs. The triply-negatively-charged Ga vacancy, V _Ga ^3– , has been emphasized, since it dominates Ga self-diffusion and Ga-Al interdiffusion under intrinsic and n-doping conditions, as well as the diffusion of Si donor atoms occupying Ga sites. Under strong n-doping conditions, the thermal equilibrium V _Ga ^3– concentration, , has been found to exhibit a temperature independence or a negative temperature dependence, i.e., the value is either unchanged or increases as the temperature is lowered. This is quite contrary to the normal point defect behavior for which the point defect thermal equilibrium concentration decreases as the temperature is lowered. This property provides explanations to a number of outstanding experimental results, either requiring the interpretation that V _Ga ^3– has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect non-equilibrium phenomena.     

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.     

Determination of the far infrared optical constants of η-doped bulk CdxHg1?xTe (CMT) by dispersive fourier transform spectroscopy

Far infrared phase and amplitude reflectivity measurements have been made on two bulk Cd_xHg_1–xTe mixed crystals with composition x=0.29 and x=0.22 by dispersive Fourier transform spectroscopy (DFTS). The results have been used to calculate the real and imaginary parts of the dielectric function (, ) from the Fresnel relations. A plasma contribution is observed in the spectra in addition to the phonon response. For both samples a broad but weak reflection band around 95–105 cm^–1 is observed as well as the expected two-oscillator response from the HgTe-like and CdTe-like optical phonons. This feature is attributed to absorption due to phonon combination bands, but it is too broad to enable assignments to be made. There is no evidence of additional features in the CdTe region due to clustering.     

Magnetic susceptibility of vanadium garnets NaPb2Co2V3O12 and NaPb2Ni2V3O12

Vanadium garnets NaPb₂Co₂V₃O₁₂ and NaPb₂Ni₂V₃O₁₂ have been successfully synthesized. The X-ray diffraction experiments indicate that these compounds have the garnet structure of cubic symmetry of space group with the lattice constant of 12.742 Å (NaPb₂Co₂V₃O₁₂) and 12.666 Å (NaPb₂Ni₂V₃O₁₂), respectively. The magnetic susceptibility of NaPb₂Ni₂V₃O₁₂ shows the Curie-Weiss paramagnetic behavior between 4.2 and 350 K. The effective magnetic moment μ_eff of NaPb₂Ni₂V₃O₁₂ is 3.14 μ_B due to Ni²⁺ ion at A-site and the Weiss constant is −3.67 K (antiferromagnetic sign). For NaPb₂Co₂V₃O₁₂, the simple Curie-Weiss law cannot be applicable. The ground state is the spin doublet and the first excited state is spin quartet , according to Tanabe-Sugano energy diagram on the basis of octahedral crystalline symmetry. This excited spin quartet state just a bit higher than ground state influences strongly the complex temperature dependence of magnetic susceptibility for NaPb₂Co₂V₃O₁₂.     

Far infrared reflection spectra in narrow-gap semiconductors

Far infrared reflection spectra of Cd_XHg_1–X Se are measured in the region 20 to 600 cm^–1 at temperatures between 5 and 77 K. Reflection spectra are explained well by the dynamic dielectric function which is constructed as a sum of ₈–₈ interband, intraband and phonon contributions. The plasmon-LO phonon coupling effect is also discussed.     

ArF laser CVD of hydrogenated amorphous silicon: The role of buffer gases

ArF laser-induced CVD has been employed to generate hydrogenated amorphous silicon (a-Si:H) from Si₂H₆ gas dilute with He, Ar, or H₂. The formation of amorphous films or powder is found to depend critically on the kind of buffer gas, the stationary total and partial gas pressures, and the substrate temperature. These dependences have been investigated in the 1–5 Torr pressure and 100–400 °C temperature ranges. They are semiquantitatively discussed in terms of ArF laser photolysis of disilane, gas heating by heat flow from the substrate and laser irradiation, diffusion, and gas phase polymerization. Furthermore, photo ionization has been observed but found irrelevant for the a-Si:H layer properties. The photo and dark conductivities ( _ph, _d) of the semiconductor layers are determined by the substrate temperature. The _ph values range between 10^–7 and 10^{–4 –1} cm^–1 and the _d values between 10^–11 and 10^{–8 –1} cm^–1. The maximum ratio _ph/ _d amounts to 4×10⁴. The layers are further characterized by their optical band gap and activation energy. The layer properties are compared to literature values of amorphous films prepared by various photo, HOMO, and plasma CVD methods.     

Some Results of Investigations into High-Rate Hot Extrusion of Malleable Cast Iron

Based on the results of our investigations, an optimal temperature and strain-rate regime of high-rate extrusion is established (with strain rates V ₀ = 10–100 m/s, temperatures T ₀ = 800–1000°C, and elongations = 1.94–4.0) in which a deformable material (KC 37-12 malleable cast iron) manifests a high ductility. In addition, the mechanical properties – the compression strength _cs and the Brinell hardness – increase 2–3 times compared to those of cast specimens. Based on the data obtained, a novel method of rod extrusion from malleable cast iron has been developed.