Effect of alloying with boron on the phase composition and structure of Ni3Al

The structure of Ni₃Al alloy prepared by self-propagating high-temperature synthesis is studied by means of transmission electron diffraction, scanning microscopy, and X-ray structural analysis. The effect of alloying with boron on the morphology of the alloy structure is established. The grain and defect structures are investigated. The dislocation density and the internal stress are measured.     

XRD, TDPAC and LAPW study of Hf10B2 under high pressure

The crystallographic structure and electronic properties of Hf¹⁰B₂ were studied as a function of pressure by combining X-ray diffraction measurements with full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed up to a pressure of 30.8 GPa, with a total volume contraction of V/V ₀?=?0.85 and a bulk modulus value of B ₀?=?232 ±13 GPa. The calculated V _zz value at the hafnium site is linearly increasing as a function of the pressure induced volume reduction, while the V _zz value at the boron site stays almost zero. The major contribution to the V _zz value at the hafnium site comes from a p–p contribution next to the probe nucleus, with a relatively large d–d contribution of about 25%. This unusual large d–d contribution arises from the hafnium p–d electrons coupling.     

Auger parameter of hafnium in elemental hafnium and in hafnium oxide

X-ray photoelectron spectroscopy has been used to determine the Auger parameters in elemental hafnium and in hafnium oxide (HfO₂). The zirconium L_α line has been used as a source of excitation to study the 3d core levels of hafnium, the 1s core level of oxygen, and the X-ray excited MNN Auger region of hafnium and KVV Auger region of oxygen. The Auger parameters for hafnium and oxygen have been determined from these spectral data. In case of oxygen, the Auger parameter has been compared with the corresponding value in water. The change in the Auger parameter is observed to be negative for hafnium and positive for oxygen. We have shown that the opposite signs of the Auger parameters in binary systems can be utilized to determine the direction of charge transfer between the constituents. This is consistent with the chemical shift due to charge transfer. This chemical shift in the core level has been evaluated by subtracting the relaxation shift from the experimentally observed core level shift. It is found to be positive for the 3d_5/2 core level of hafnium in the oxide indicating a charge transfer from hafnium to oxygen in the oxide. The observations are consistent with Pauling’s electronegativity criterion.     

Surface structure and catalytic activity of rapidly quenched amorphous iron based alloys: II. Effect of hydrochloric acid treatment

The surface structure of Fe₈₀B₂₀ and Fe₄₀Ni₄₀B₂₀ amorphous alloys in the as-received state and after HCI treatment was studied by X-ray photoelectron spectroscopy. The surface composition and valence state determined in depth were related to the catalytic activity and selectivity revealed in CO+H₂ reaction. It was established that on the shiny side of the Fe₈₀B₂₀ sample deep oxidation took place due to the removal of the boron oxide layer by HCI etching, while on the dull side the originally porous layer became smooth resulting in the formation of a compact oxide layer decreasing thereby the accessible metal sites. On the other hand, on the Fe₄₀Ni₄₀B₂₀ alloy, after removing the prevailing boron oxide and iron oxide layer, an increased number of nickel and iron sites was responsible for the enhanced catalytic activity. Accordingly, on pure iron-boron alloy the catalytic activity considerably decreased whereas on iron-nickel-boron alloy not only a six-fold activity increase was measured but the olefin selectivity was significantly diminished due to the hydrogen activating function of nickel.     

Effect of boron in Fe 70 Al 30 nanostructured alloys produced by mechanical alloying

The substitution of aluminum by boron in the Fe₇₀Al₃₀ system prepared by high energy ball milling is studied when the B content ranged from 0 up to 20 at. %, and the milling times were 24, 48 and 72 h. X-ray diffraction (XRD) patterns of Fe₇₀Al₃₀ showed a predominant bcc structural phase with a lattice parameter larger than that of α-Fe. A second (tetragonal) phase arose with the addition of boron. It is associated to the existence of (Fe, Al)₂B, although the values of the lattice parameters are slightly different from those found in the literature. This phase shows high stability; its lattice parameters and the Mössbauer parameters do not show notable variations, either with milling time or composition. It was also evidenced that an increase of boron content and of milling time produced a decrease of the lattice parameter of the Fe-Al bcc structure. This is in agreement with the small atomic radius of boron in comparison with that of aluminum. This also allows boron to occupy interstitial sites in the lattice, increasing the grain size and giving rise to the ductile character of the alloy. On the other hand, 300 K transmission Mössbauer spectra (TMS) were fitted, for low boron concentrations (<8 at.%), with a hyperfine field distribution (HFD) associated with the bcc phase. For high boron content (≥8 at.%), a magnetic component related to the tetragonal phase is added and its broadened lines are attributed to the disordered character of Fe₂B, probably induced by the milling process.     

Low-Spin Ferriheme Models of the Cytochromes: Correlation of Molecular Structure with EPR and Mössbauer Spectral Parameters

The electronic properties of the intermetallic compound HfCo₃B₂ were investigated using combined TDPAC measurements and first principles LAPW calculations. The V _zz value at the hafnium site is determined from dominant positive p–p contribution, with less than 20%, negative s–d and d–d contributions. Based on the calculated density of state (DOS) at 0 K, a band contribution (γ _band) of 7.26 (mJ/mol/K²) to the value of the electronic specific heat coefficient (γ) was obtained. This relatively low γ _band value is attributed to the hybridization between hafnium d-states, boron 2p-states and cobalt 3d-states, formed at the energy interval below E _Fermi. This hybridization, together with the dip in the DOS around E _Fermi, implies a possible reduction of the low temperature magnetic moment in this compound.     

Features of the surface layers of TiNi-based alloy thin ribbons

The chemical composition of the surface of TiNi-based alloys in the form of ribbons produced by rapid melt quenching in oxygen-containing environment has been investigated. It is shown that titanium oxide is formed on the Ti₅₀Ni₂₅Cu₂₅ alloy surface, while on the Ti_39.2Ni_24.8Cu₂₅Hf₁₁ alloy surface titanium and hafnium oxides are formed. Atomic-force microscope images reveal crystalline structures of titanium oxide with sizes of up to 500 × 500 nm² on the surface of the Ti₅₀Ni₂₅Cu₂₅ sample. After removing the surface oxide layer by ion etching, the ratio of elements becomes close to the stoichiometric composition.     

Structural, dielectric and electromechanical study of Hf-substituted BaTiO3 thin films fabricated by CSD

Hafnium-substituted barium titanate thin films were deposited on platinized silicon substrates. Two different concentrations of solutions (0.1 M and 0.3 M) were used to deposit films of various compositions Ba(Ti_1-x,Hf_x)O₃ (x=0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4). The microstructure of the films depended on the concentration of the solution. Lower concentration (0.1 M) solutions led to columnar films, but with higher hafnium percent compositions the columnar structure was lost. The films which were derived from the 0.1 M concentration solutions had better dielectric and electrical properties compared to the films derived from a higher concentration (0.3 M). All the films were found to be polycrystalline in nature. The dielectric constant of the films was found to decrease with higher amounts of hafnium substitution. From the I–V characteristics it is noticed that the leakage decreases by almost four orders of magnitude with a hafnium substitution of 40%. The d₃₃ values of the films were between 23 and 5.6 pm/V for the different films. PACS 68.55.-a; 81.20.Fw; 77.84.Dy; 77.55.+f     

X-ray absorption and emission spectroscopy at the Hf L1 edge of hafnium-(silicon)-oxide ultra-thin films

X-ray absorption and emission spectroscopic study at the Hf L₁ edge was applied to investigate the local structure around hafnium atoms in Hf(Si)O_x ultra-thin films, which are the most promising candidates for the high-k gate dielectric material of next generation CMOS devices. HfSiO_x showed an extra absorption above the Hf-L₁ threshold, which is not seen in HfO_x. HfSiO_x also had stronger Compton scattering peak in Hf-Lγ emission region, and smaller Hf-Lγ₂/Lγ₃ ratio, compared with those of HfO_x. These differences should be caused by partial replacements of hafnium atoms by silicon atoms as the second nearest neighbors of a hafnium atom.     

Mechanism of crystallization of the Ni70Mo10B20 alloy above the glass transition temperature

The phase transformations occurring in the Ni₇₀Mo₁₀B₂₀ alloy in the course of heating above the glass transition temperature are investigated using x-ray diffraction, transmission electron microscopy, high-resolution electron microscopy, and differential scanning calorimetry. It is shown that annealing of the alloy above the glass transition temperature leads to segregation of the amorphous phase into regions enriched with and depleted in molybdenum and/or boron. An increase in the temperature or time of annealing is accompanied by primary crystallization in regions of each type. Crystallization of the regions enriched with molybdenum results in the formation of face-centered cubic crystals of a molybdenum solid solution in nickel (phase 2). Nickel boride crystallizes in the regions enriched with boron. The face-centered cubic phase (phase 1), which is similar to pure nickel, crystallizes in the regions depleted in molybdenum and boron. Nanocrystals of phase 1 are free of defects. Nanocrystals of phase 2 with larger sizes contain a great number of defects.     

Band structure of the superconducting MgB2 compound and modeling of related ternary systems

Band structure of a novel superconductor—magnesium diboride—is studied by the self-consistent FP-LMTO method. Density of states near the Fermi level of MgB₂ and its electronic properties are governed by the metal-like boron 2p orbitals in the planar network of boron atoms. The modification of the band structure of MgB₂ upon doping the boron (with Be, C, N, and O substitutional impurities) and the magnesium (with Be, Ca, Li, and Na substitutional impurities) sublattices or upon the introduction of structural vacancies (boron nonstoichiomety) is analyzed. The electronic structures of MgB₂ and hypothetical CaB₂ are also studied as functions of pressure.     

Theoretical calculations on structural and electronic properties of BGaAsBi alloys

The structural and electronic properties of cubic B _x Ga_1?x As_1?y Bi _y alloys with bismuth (Bi) concentration of 0.0625, 0.125, 0.1875 and 0.25 are studied with various boron (B) compositions by means of density functional theory (DFT) within the Wu-Cohen (WC) exchange correlation potential based on generalized gradient approximation (GGA). For all studied alloy structures, we have implemented geometric optimization before the volume optimization calculations. The obtained equilibrium lattice constants and band gap of studied quaternary alloys are investigated for the first time in literature. While the lattice constant behavior changes linearly with boron concentration, increasing small amount of bismuth concentration alter the lattice constant nonlinearly. The present calculation shows that the band gap decreases with increasing bismuth concentration and direct band gap semiconductor alloy became an indirect band gap with increasing boron concentration. From the band offset calculation we have shown that increasing B and Bi concentration in host GaAs reduced the valance band offset in a heterostructure formed by GaAs and studied alloys.     

Photoemission and electronic structure of Mo,Ru and Amorphous MoRuB and MoRuP

The electronic structures of molybdenum, ruthenium and amorphous Mo₄₈ Ru₃₂ B₂₀ and Mo₄₀ Ru₄₀ P₂₀ are investigated by the XPS and UPS techniques. The experimental results of pure elements are in agreement with previous band calculations. The valence bands of the amorphous alloys are quite comparable to those obtained from pure Mo and Ru assuming hypothetical alloys. For the investigated alloys, the electronic DOS's at the Fermi level are intermediate between those of transition metal components. The disordering on the band structure, due to alloying effects, is found to be larger for the phosphorus based alloy than for the boron one. A qualitative band model can explain the various observed properties; the experimental results are also discussed in relation with the atomic volumes.     

Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

The negative electrode development for a Ni–MH battery prototype

The negative electrode development for a nickel-metal hydride battery (Ni–MH) prototype was performed with the following procedure: (1) the Lm_0.95Ni_3.8Co_0.3Mn_0.3Al_0.4 (Lm=lanthanum rich mischmetal) intermetallic alloy was elaborated by melting the pure elements in an induction furnace inside a boron nitride crucible under an inert atmosphere, (2) the obtained alloy was crushed and sieved between 44 and 74 μm and mixed with teflonized carbon; (3) the compound was assembled together with a current collector and pressed in a cylindrical matrix. The obtained electrode presented a disc shape, with 11 mm diameter and approximately 1 mm thickness. The crystalline structure of the hydrogen storage alloy was examined using X-ray diffractometry. The measured hcp lattice volume was 1.78% larger than the precursor LaNi₅ intermetallic alloy, increasing the available space for hydrogen movement. Energy dispersive spectroscopy (EDS) and scanning electronic microscopy (SEM) measurements were used before and after hydriding in order to verify the alloy sample homogeneity. The negative electrode was electrochemically tested by using a laboratory cell. It activates almost totally in its first cycle, which is an excellent characteristic from the commercial point of view. The maximum discharge capacity reached was 314.2 mA h/g in the 10th cycle.     

Photocatalytic Activities of Boron Doped Titanium Dioxide Nanoparticles and its Composite with Polyaniline

Abstract

Titanium dioxide (TiO₂) was doped with a nonmetalic element, boron (B), and the boron doped TiO₂ (B-TiO₂) was combined with polyaniline (Pani) through an in-situ polymerization technique. The photocatalytic activity of the prepared samples was monitored by the degradation of methylene blue under UV light irradiation. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to reveal the effect of boron doping on the crystalline and chemical structure of the photocatalyst, respectively. The morphological and elemental compositional characteristics of the samples were evaluated using field emission scaning electron microscopy (FE-SEM) and energy dispersive x-ray analysis. The optical band gap energy of the prepared samples was obtained by UV-Visible (UV-Vis) spectroscopy. B-TiO₂ exhibited enhanced photocatalytic performance compared to the undoped photocatalyst. Furthermore, compared with TiO₂ and B-TiO₂, Pani/B-TiO₂ displayed superior photocatalytic activity. The composite achieved almost 26% methylene blue degradation within 150?minutes. Although the boron doping enhanced the crystallinity of TiO₂ slightly, it did not affect the morphology. FTIR confirmed the presence of tri-coordinated interstitial boron in the Ti–O–B bonds. The UV-Vis spectra displayed a red shift with the incorporation of the boron atoms. The incorporation of the boron atoms in the TiO₂ crystal structure are suggested to promote the separation of the photoinduced electron-hole pairs, a possible reason for the enhanced photocatalytic activity. B-TiO₂ and its composite with polyaniline could be considered as a promising photocatalyst to remove organic dyes from the wastewater.     

Nanoscale order in GaAs:(B, Sb)

Nanoscale order caused by self-assembling of 1B4Sb and 4B10Sb clusters in GaAs:(B, Sb) is described. Self-assembling occurs in wide ranges of temperature and impurity concentration. Co-doping with boron and Sb isoelectronic impurities transforms GaAs into GaAs-rich B_xGa_1−xSb_yAs_1−y quaternary alloy. The self-assembling conditions are obtained from 0 to 800 °C with boron and Sb concentrations from x=1×10^–5 to x=2×10^–4 and from y=5×10^–4 to y=0.01, respectively. If Sb content is much larger than that of boron almost all boron atoms are in 1B4Sb clusters up to 800 °C and other boron impurities are isolated. If boron content is nearly equal or larger than that of Sb the formation of 4B10Sb clusters is preferential.     

Studies on the valence state of Ce and Eu in some new boron and silicon containing rare earth intermetallic compounds

Compounds of the formula RPd₃B _x (R=rare earth with 0?x?1) and RPd₃Si _x (R=La, Ce, Eu with 0?x?0.3) can be prepared by alloying boron or silicon with parent RPd₃ compounds. Addition of boron (silicon) does not change the structure but results in lattice expansion. The valence state of Ce in CePd₃ and that of Eu in EuPd₃ is strongly influenced by boron and silicon. Ce is known to be in a valence fluctuating state in CePd₃ while Eu is trivalent (J=0) in EuPd₃. The increase in the lattice parameter as a function of boron concentration is observed to be larger in CePd₃B _x and EuPd₃B _x compared to that in other RPd₃B _x alloys giving the first indication of the change in the valence state of Ce and Eu. This is confirmed from susceptibility measurements. With the addition of boron, susceptibility increases and the effective paramagnetic moments approach the values corresponding to Ce³⁺ (J=5/2, μ_eff=2.54 μ _B ) and Eu²⁺ (J=7/2, μ_eff=7.94 μ _B ) in the two alloy systems CePd₃B _x and EuPd₃B _x respectively. In the case of europium alloys,¹⁵¹Eu Mössbauer studies point out the importance of near-neighbour environment effects. Further, in EuPd₃B, where all the europium ions are crystallographically equivalent, a single Mössbauer line, with an isomer shift characteristic of europium ions in valence-fluctuating state, is observed at 300 K. However, at 88 K the Mössbauer absorption splits into two lines corresponding to europium ions in two valence states,e.g. divalent- and trivalent-like. Such a behaviour indicates thermally-induced charge ordering of europium ions. Addition of silicon to CePd₃, like boron, results in unusual lattice expansion and changes the valency of cerium towards 3⁺. the valence change is further corroborated by susceptibility measurements. In EuPd₃Si _x alloys, susceptibility and Mössbauer studies indicate that in the limiting single phase alloy EuPd₃Si_0.25 the europium ions are on the verge of valence instability. Susceptibility results on CeRh₃B _x alloys are also presented.     

TDPAC investigation on thermally related HfF4.3H2O and HfO2

The hyperfine quadrupole interaction of HfF₄.3H₂O at Hf sites is investigated from 14 to 820 K. No transitions have been found. After the complete dehydration of this compound at 393 K, chemical reactions take place which give rise to hafnium oxifluorides and metastable forms of hafnium oxide. Heating treatments at increasing temperatures make HfO₂ turn into its monoclinic phase.     

The effect of silicon on the structure and properties of Fe-Cr-Co permanent magnet alloys

The influence of silicon in amounts of up to 4.33 wt% was studied in terms of its effect on micro- and macrostructure, on non-metallic inclusions, on mechanical hardening and on magnetic properties of Fe-28Cr-24Co alloy of equiaxial grain structure and of partially ordered structure-the so-called semicolumnar structure. Optimum magnetic properties in the examined alloy are attained with silicon content Si = 1.04 wt%. Magnetic properties of an alloy of semicolumnar structure are markedly superior to those of the alloy devoid of that structure. With up to 1.04 wt% of silicon, the macrostructure of the alloy remains practically unchanged, while with higher contents of silicon a refinement of the structure takes place. The stereometric parameters of non-metallic inclusions (Al₂O₃, SiO₂, Al₂O₃·SiO₂) increase with silicon contents Si > 1.04 wt%. The hardness of the alloy after homogenizing is practically constant up to silicon content Si = 1.65 wt%, but it increases slightly with Si > 1.65 wt%. The examined alloy with silicon up to 1.65 wt% is ductile in the quenched state and could also be cold-worked.