Structure changes in Al80Ni15Y5 amorphous alloy

The structure of Al₈₀Ni₁₅Y₅ amorphous alloy at various temperatures have been studied with X-ray diffraction methods. The obtained scattered intensities, structure factors, pair correlation functions and main structure parameters have been analyzed. Temperature dependences of the parameters suggest formation of Al, Al₃Ni and Al₂₃Ni₆Y₄ phases upon crystallization of an amorphous alloy.     

Band alignment at the interfaces of Al2O3 and ZrO2-based insulators with metals and Si

Internal photoemission of electrons was used to determine the band alignment in metal (Mg, Al, Ni, Cu, Au)-oxide-silicon structures with Al₂O₃- and ZrO₂-based insulators. For Al₂O₃- and ZrO₂ layers grown on Si by atomic layer deposition the barrier height between the Si valence band and the oxide conduction band was found to be 3.25 and 3.1 eV, respectively. Thermal oxidation of the Si/oxide stacks results in a barrier height increase to ≈4 eV for both cases due to formation of a silicate interlayer. However, there is a significant sub-threshold electron emission both from silicon and metals, indicating a high density of states in the band gap of the insulators. These states largely determine the electron transport across metal oxides and may also account for a significant dipole component of the potential barrier at the metal/ZrO₂ and metal/Al₂O₃ interfaces.     

XPS-study of the interaction of air-oxygen with platinum surfaces

The differences in the XPS spectra of the band regions Pt4f, Ols and VB between cleaned and air exposed polycrystalline platinum samples are discussed. After defined exposure it appears PtO_ads. and a cation configuration of 5d⁸ 6s¹ for platinum. This can be shown by line shapes, especially by the double peak structure of oxygen lines and by the asymmetrical tail on the high binding energy region of Pt4f combined with valence band results.     

Magnetocaloric effect in nano- and polycrystalline La0.8Sr0.2MnO3 manganites

The sol–gel method is applied to prepare the polycrystalline La_0.8Sr_0.2MnO₃ manganite and to reduce grain sizes of nanocrystalline sample down to 23 nm. The magnetocaloric effect was determined from isothermal magnetization measurements. Transition from the polycrystalline to nanocrystalline structure reduces the size of magnetocaloric effect and markedly broadens the temperature interval over which it occurs. The relative cooling power RCP(S) = 35 J/kg in polycrystalline manganite remains almost the same in the nanocrystalline case.     

Influence of Gd and Fe on crystallization of Al87Y5Ni8 amorphous alloy

Crystallization of amorphous Al-based alloys (Al-Y-Gd-Ni-Fe) was investigated by applying differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high resolution electron microscopy (HREM). It was shown that the crystallization in the examined alloys proceeds in three stages (DSC maxima). The two first stages are attributed to formation of solid solution of fcc Al(RE) nanograins in amorphous matrix. In the third stage the precipitation of ternary compound Al₁₉Ni₅RE₃ of the orthorhombic Al₁₉Ni₅Gd₃-type structure was observed. A partial substitution of Ni by Fe causes a change of stoichiometry and crystal structure of the ternary compounds: Al₈TM₄RE (TM = Fe, Ni; RE = Y, Gd) of the tetragonal ThMn₁₂ (Al₈Mn₄Ce)-type structure. A partial replacing of Y atoms by Gd in the Al₈₇Y₅Ni₈ based alloy shifts the Al(RE) nanocrystallization to lower temperatures. In contrast to this a partial replacing of Ni by Fe shifts the nanocrystallization to higher temperatures.     

Electronic structure investigation of V1−xNbxO2 mixed oxide by XES and XPS

The mixed oxide system V_1−xNb_xO₂ (x ≦ 0.12) has been studied by X-ray and photo-emission spectroscopy as a function of the composition. The metal L valence band spectra (VL_III and NbLβ_2.15) with increasing Nb concentration change their width and relative band intensity substantially pointing to charge flow and hybridization effects. The XPS valence band for x ≧ 0.04 indicates a total d band shift of 0.4 eV relative to smaller Nb concentrations. The measured core level spectra at higher Nb doping x ≈︁ 0.10 support the expected existence of V³⁺-Nb⁵⁺ pairs. A comparison of different X-ray spectra and the XPS valence band spectrum for x = 0.08 exhibits a more stronger V3d localization relative to Nb4d, favouring charge transfer and bonding variations with Nb doping. Our spectroscopial data confirm the established ideas concerning the electronic structure of rutile-like compounds and its change at the phase transition point.     

Amorphization and crystallization processes of the ball-milled Al–Y–Fe–TM alloys (TM = Ni,Co, Cu,and Fe)

High-energy ball milling was used to synthesize aluminum-based alloys containing amorphous and nanocrystalline phases to investigate the compositional effects of transition metals (TM) on the amorphization and crystallization processes of the ball-milled Al₈₅Y₇Fe₅TM₃ alloys (TM = Ni, Co, Cu, and Fe) were investigated. The crystallization kinetics of the ball-milled Al–Y–Fe–TM nanocomposite powders were studied using differential scanning calorimetry (DSC). The DSC results of Al₈₃Y₇Fe₅Ni₅ show that the crystallization temperature and the activation energy of crystallization are 668 K and 310 kJ/mol, respectively. In-situ high-temperature X-ray diffraction showed that the crystallization was a complex process involving growth of the nanocrystalline phase along with crystallization of the amorphous matrix phase.     

Short-range atomic order in the surface layer of sputter-deposited Al0.6W0.4 thin film investigated using directional elastic peak electron spectroscopy

A mechanism of creating maxima in directional elastic peak electron spectroscopy (DEPES) polar profiles for textured polycrystalline samples and for amorphous samples with a short-range atomic order is proposed and discussed. DEPES was used in investigating the atomic order in Al and W polycrystalline samples. The maxima found in DEPES polar profiles correspond with the texture expected for these samples on the basis of literature data. A method of processing DEPES data of amorphous metallic alloy with a short-range atomic order is proposed and successfully used for an Al_0.6W_0.4 alloy. The results obtained indicate that nanocrystals with an average linear size in the range of 1 nm and with a particular orientation with respect to the sample surface are present in the surface layer of the sample investigated. A concentration of nanocrystals with such orientation equal to 1.9 × 10¹⁹/cm³ was found when using of the contrast obtained for the maximum in the DEPES polar profile, corresponding to an incidence angle of zero. The contrast of DEPES profiles for the Al_0.6W_0.4 sample increases remarkably during annealing at 373 K. An increase in the amount of preferentially-oriented nanocrystals is suggested as the probable reason for this increase.     

X-ray diffraction study of amorphous alloys Al–Ni–Ce–Sc with using Ehrenfest’s formula

The effect of replacement of Ce by Sc in the amorphous Al₈₅Ni₁₀Ce₅ alloy on its structure has been studied. The replacement was shown to result in increasing the coordination number in the first coordination sphere, changing the type of short-range order. A splitting the first peak of the function of radial atom distribution into two subpeaks made it possible to determine separately the coordination number for the atom pair groups Ce–Al, Sc–Al, Al–Al and Ni–Al, Al–Al. The structure of the amorphous alloys Al₈₅Ni₁₀Ce_5−xSc_x (x = 0, 1, 5) was determined using X-ray diffractometry combined with application of Ehrenfest’s formula, which allowed us to directly determine the first coordination sphere radius from data on the structure factor and some cluster parameters obtained from the prepeak on the structure factor curve.     

Effect of Ni-addition on the crystallization behavior and the oxidation resistance of Zr-based metallic glasses below the crystallization temperature

The crystallization behavior of Zr_65.0Al_7.5Ni_10.0Cu_17.5 metallic glasses by addition of Ni with 753 K annealing treatment and its effect on the oxidation resistance around the supercooled liquid region at 663 K were studied. By annealing at 753 K, the nanocrystalline phase of bct-Zr₂Cu precipitates was observed in the Zr_65.0Al_7.5Cu_27.5 specimen, while microstructures consisting of finer nanocrystalline bct-Zr₂Cu, fcc-Zr₂Ni and Zr₆Al₂Ni formed in the Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen. The oxidation resistance of the melt-spun Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen was improved by addition of Ni, which is evidenced by less mass gain and thin oxide scale. The microstructural refinement by the formation of numerous nanocrystalline phases of bct-Zr₂Cu, fcc-Zr₂Ni and Zr₆Al₂Ni from the matrix resulted in an improvement of the oxidation resistance, whereas a relative coarse nanocrystalline phase consisting of bct-Zr₂Cu exhibited fast oxidation along grain boundaries. Although the oxide species for both specimens were composed of a large amount of CuO/Cu₂O, some tetragonal and monoclinic-ZrO₂ as well as a minor amount of the oxide state of Cu³⁺, the amount of oxides especially for ZrO₂ in the Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO₂.     

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al₂O₃ and ZrO₂ films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al₂O₃) or 0.6 nm (ZrO₂), the band gaps of the Al₂O₃ and ZrO₂ films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al₂O₃/Si and ZrO₂/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al₂O₃ and Zr 3p3 in ZrO₂ are 2.7 and 2.0 nm, respectively.     

Glass forming ability of the Al–Ce–Ni system

In the present work, the glass forming ability (GFA) and its compositional dependence on Al–Ni–Ce system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al₈₅Ni_15?XCe_X (X = 4,5,6,7,10), Al₉₀Ni₅Ce₅, Al₈₉Ni_2.4Ce_8.6, Al₈₀Ni_15.6Ce_4.4 and Al₇₈Ni_18.5Ce_3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al–Ni–Ce system alloys were enhanced by increasing the solute content and specifically the Ce content.     

AlxGa1−xN bulk crystal growth: Crystallographic properties and p–T phase diagram

The recent results on the growth of the Al_xGa_1−xN bulk single crystals (0.22≤x≤0.91) from solution in liquid Ga under high nitrogen pressure are discussed. We focus on the influence of temperature and the choice of the Al source on the crystal growth. The experiments involving different sources of aluminum such as Al metal, pre-reacted polycrystalline Al_yGa_1−yN and AlN powder are compared. The best results were achieved using pre-reacted polycrystalline Al_yGa_1−yN or/and AlN. Single-crystal structure refinement data of these Al_xGa_1−xN crystals are presented. We also update the p–T phase diagram of (Al,Ga)N compound at high N₂ pressure for various Al content, which is the basis for (Al,Ga)N synthesis.     

Lightweight Ti–Zr–Be–Al bulk metallic glasses with improved glass-forming ability and compressive plasticity

A series of lightweight Ti–Zr–Be–Al bulk metallic glasses (BMGs) have been developed through the addition of Al to Ti–Zr–Be ternary glassy alloy. By replacing Be with Al, the critical size of the glassy rod has been increased from 5 mm for Ti₄₁Zr₂₅Be₃₄ alloy to 7 mm for Ti₄₁Zr₂₅Be₂₉Al₅ alloy, while the yield strength of Ti₄₁Zr₂₅Be_34 ? xAl_x (x = 2–10) has been greatly enhanced, resulting in a significant increase of the specific strength which is defined as yield strength/density. Among these newly developed Ti–Zr–Be–Al BMGs, Ti₄₁Zr₂₅Be₂₆Al₈ glassy alloy exhibits a high specific strength of 4.33 × 10⁵ Nm/kg and a very large compressive plastic strain of 47.0%, which are much larger than those (3.69 × 10⁵ Nm/kg and 2.9%, respectively) for Ti₄₁Zr₂₅Be₃₄ glassy alloy. The present results show that Al is an effective alloying element for improving the glass-forming ability (GFA) and mechanical properties of Ti-Zr-Be glassy alloy.     

Structure of amorphous LaNi5D3.3 studied by neutron and X-ray diffraction

In situ neutron and X-ray diffraction measurements in a D₂ gas atmosphere at a constant pressure of 1 MPa were performed on amorphous LaNi₅D_3.3, which was prepared by mechanical alloying in a D₂ gas atmosphere. Reverse Monte Carlo (RMC) simulation based on the neutron and X-ray diffraction data was applied to construct a three-dimensional atomic arrangement of this amorphous alloy. The RMC model shows that more than 90% of the deuterium atoms occupy tetrahedral sites consisting of La and/or Ni atoms. Furthermore, the local environments around the Ni and La atoms were investigated by Voronoi polyhedral analysis of the RMC configuration of the metal atoms. The results show the presence of a number of prismatic-like polyhedra around a Ni atom.     

Physical properties of Zn‐ 22 wt.% Al‐ x wt.% Ce melt spun eutectoid alloy

Zn‐ 22 wt.% Al (Zn ‐ 40 Al in atomic%) eutectoid alloys with different Cerium (Ce) contents of 0, 1, 2, and 6 (in wt.%), 0.35, 0.70 and 2.1 (in atomic%) were rapidly solidified by melt spun technique. The effects of high cooling rate and alloying element (Ce) on microstructure of the studied alloys were analyzed by X‐ray diffractometry (XRD), scanning electron microscopy (SEM) and electrical resistance measurements. The results showed that the dendrites as well as grains size were refined by the additions of Ce. The main phases in melt spun alloys were α‐Al and η‐Zn, in addition to intermetallic CeZn₅ and Al₄Ce. Additional metastable intermetallic Al_0.71Zn_0.29 phase has been observed only for melt spun alloy of 6 wt.% Ce content. XRD peaks of melt spun alloys demonstrated a considerable broadening with percentage of Ce due to the grain refinement and lattice distortion. Moreover, increase of Ce content results in a decrease of Al lattice constant which could be related to formation of supersaturated solid solution of Zn and/or Ce in α‐Al. Crystallite size of all phases were in the range of nanometer scale which reflects the role of the high cooling rate and the existence of Ce as alloying element for producing nanocrystalline structure. Resistance measurements of melt spun alloys show that the relative resistance rate for the alloys of higher Ce content relaxed faster to lower value than that of lower Ce content. Electrical resistance and microstructure exhibit strongly Ce content dependence.     

Investigation of 1 S1/2O,1 S1/2C and 2 P3/2Ni states of argon ion implanted nickel metal

Polycristalline Ni samples were bombarded by 30 keV Ar ions with dose rates from 10¹⁶ ions/cm² to 10¹⁷ ions/cm². The investigation of the electronic states 1 S_1/2O, 1 S_1/2C and 2 P_3/2Ni was made by X-ray photoemission spectroscopy (XPS). The XPS core level spectra show features refering to different chemical compounds of oxygen and carbon with nickel. We have studied the change of this spectrum structure dependent on distance of the sample surface for various doses of implantation.     

Investigation of glass forming ability in Ce–Al–Ni alloys

The compositional dependence of the glass forming ability (GFA), the correlation between their GFA and the GFA related parameters, and the thermal stability of the Ce–Al–Ni alloys were investigated. Rapidly quenched Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) ribbons were prepared by melt spinning, and their phase transformations were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The experimental results indicated that the GFA of Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) alloys increased firstly and then decreased with the increasing of the Al content up to 20 at.%, respectively. It was found that only one parameter, F₁, in evaluated currently available empirical GFA parameters searching for metallic glasses with a good GFA, can reflect the GFA of the Ce–Al–Ni alloys. It was indicated that the thermal stability of alloy with fully amorphous maybe lower than that of alloy with partial amorphous.     

Electrochemical behavior of different structural states of the alloy Ti60Ni40

Potentiodynamic polarization studies were carried out on nanocrystalline I, nanocrystalline II and nanocrystalline III states having crystallite size 35 ± 5 nm, 18 ± 2 nm and 10 ± 2 nm of the alloy Ti₆₀Ni₄₀ in 1 M H₂SO₄ aqueous medium. It was observed that the nanocrystalline III state exhibits superior corrosion resistance as compared to the nanocrystalline II and nanocrystalline I states of the alloy Ti₆₀Ni₄₀. XPS studies were also performed after corrosion test and it was observed that nanocrystalline III state contains only Ti²⁺ and Ti⁴⁺ species whereas nanocrystalline I and nanocrystalline II state contains Ti²⁺, Ti³⁺and Ti⁴⁺ along with some unoxidized metallic Ti⁰ in the case of nanocrystalline I state. Thus the small crystallite size and the presence of only Ti²⁺ and Ti⁴⁺ species in the form of TiO and TiO₂ leads to the formation of a protective oxide film which is adherent, stable and improves the corrosion resistance of the nanocrystalline III state of the alloy Ti₆₀Ni₄₀.     

XPS characterization of corrosion films formed on the crystalline, amorphous and nanocrystalline states of the alloy Ti60Ni40

X-ray photoelectron spectroscopy investigations were carried out on the crystalline, amorphous and nanocrystalline states of the alloy Ti₆₀Ni₄₀ after corrosion test in 1 M HNO₃ aqueous medium using potentiodynamic polarization method. Polarization plots revealed that the nanocrystalline state is more corrosion resistant than the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀. The XPS characterization of the oxide film formed after corrosion tests revealed that a multiple phase oxide film is formed on the crystalline and amorphous specimens of the alloy Ti₆₀Ni₄₀ consisting of Ti²⁺, Ti³⁺ and Ti⁴⁺ species along with some unoxidized Ti in metallic form (Ti⁰) in the case of crystalline specimen whereas the oxide film formed on nanocrystalline specimen consists of only Ti²⁺ and Ti⁴⁺ species. The high corrosion resistance of nanocrystalline state is attributed to the presence of fewer oxide species in the oxide film than that of the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀.